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Based on a closing price of $24.24 per share on June 28, 2013. Excludes 13,581,132 shares of the registrant's Common Stock held by executive officers, directors and any stockholders whose ownership exceeds 5% of registrant's Common Stock outstanding at June 28, 2013. Exclusion of such shares should not be construed to indicate that any such person possesses the power, direct or indirect, to direct or cause the direction of the management or policies of the registrant or that such person is controlled by or under common control with the registrant.

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 109,976	$ 19,906
Short-term investments, available-for-sale		9,849
Accounts receivable	248	783
Prepaid and other current assets	2,765	983
Deferred financing costs, current portion	20	33
Total current assets	113,009	31,554
Property and equipment, net of accumulated depreciation	338	407
Deposits and prepaid assets, less current portion	30	22
Deferred financing costs, less current portion	10	48
Total assets	113,387	32,031
Current liabilities:
Accounts payable	2,214	1,964
Accrued liabilities	2,420	906
Loan payable, current portion	5,573	4,753
Total current liabilities	10,207	7,623
Other long-term liabilities	347	337
Loan payable, less current portion	4,294	9,867
Redeemable convertible preferred stock warrant liability		7,512
Total liabilities	14,848	25,339
Redeemable convertible preferred stock		107,723
Stockholders' equity (deficit):
Common stock, $0.001 par value, 200,000,000 and 89,700,000 shares authorized at December 31, 2013 and 2012, respectively; 26,664,972 and 1,533,996 shares issued and outstanding at December 31, 2013 and 2012, respectively	26	3
Additional paid-in capital	261,243
Accumulated other comprehensive loss		(2)
Accumulated deficit	(162,730)	(101,032)
Total stockholders' equity (deficit)	98,539	(101,031)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 113,387	$ 32,031

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2013	Dec. 31, 2012
Balance Sheets [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	89,700,000
Common stock, shares issued	26,664,972	1,533,996
Common stock, shares outstanding	26,664,972	1,533,996

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:
Contract revenue	$ 4,370	$ 16,275	$ 12,046
Collaboration and licensing revenue		17,445	55
Total revenues	4,370	33,720	12,101
Operating expenses:
Research and development	24,662	30,106	30,108
General and administrative	8,327	6,397	6,985
Total operating expenses	32,989	36,503	37,093
Loss from operations	(28,619)	(2,783)	(24,992)
Other expense:
Interest expense, net	(1,232)	(776)	(212)
Fair value adjustments to warrant liability	(6,590)	(847)	(385)
Loss on asset disposal	(4)
Net loss	(36,445)	(4,406)	(25,589)
Other comprehensive loss:
Unrealized gain (loss) on securities available-for-sale	2	2	(4)
Comprehensive loss	(36,443)	(4,404)	(25,593)
Accretion of redeemable convertible preferred stock	(34,108)	(4,357)	(9,565)
Net (loss) income attributable to common shareholders	$ (70,553)	$ (8,763)	$ (35,154)
Per share information:
Net loss, basic and diluted	$ (3.65)	$ (5.75)	$ (23.49)
Weighted-average shares outstanding, basic and diluted	19,307,422	1,524,628	1,496,262

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Total
Beginning balance at Dec. 31, 2010	$ 55,131	$ 2	$ 1,895		$ (61,504)	$ (59,607)
Share-based compensation			966			966
Issuance of redeemable convertible preferred stock	38,670
Issuance of common stock			89			89
Exercise of stock options			30			30
Dividends on redeemable preferred stock	3,235		(2,980)		(255)	(3,235)
Adjustment of redeemable preferred stock to redemption value	6,330				(6,330)	(6,330)
Comprehensive loss:
Unrealized (loss) gain on investments, net				$ (4)		(4)
Net loss					(25,589)	(25,589)
Comprehensive loss						(25,593)
Ending balance at Dec. 31, 2011	103,366	2		(4)	(93,678)	(93,680)
Share-based compensation			1,396			1,396
Exercise of stock options		1	13			14
Dividends on redeemable preferred stock	3,600		(1,409)		(2,191)	(3,600)
Adjustment of redeemable preferred stock to redemption value	757				(757)	(757)
Comprehensive loss:
Unrealized (loss) gain on investments, net				2		2
Net loss					(4,406)	(4,406)
Comprehensive loss						(4,404)
Ending balance at Dec. 31, 2012	107,723	3		(2)	(101,032)	(101,031)
Share-based compensation			3,071			3,071
Issuance of common stock		23	107,611			107,634
Exercise of stock options			1,946			1,946
Dividends on redeemable preferred stock	976		(349)		(627)	(976)
Adjustment of redeemable preferred stock to redemption value	33,132		(8,506)		(24,626)	(33,132)
Comprehensive loss:
Unrealized (loss) gain on investments, net				$ 2		2
Net loss					(36,445)	(36,445)
Comprehensive loss						(36,443)
Exercise of warrants			1,537			1,537
Conversion of redeemable preferred stock into common stock	$ (141,831)		141,831			141,831
Reclassification of redeemable preferred stock warrant liability to additional paid in capital			14,102			14,102
Ending balance at Dec. 31, 2013		$ 26	$ 261,243		$ (162,730)	$ 98,539

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical)	12 Months Ended
	Dec. 31, 2013 USD ($) $ / shares shares
Statement of Stockholders' Equity [Abstract]
Issuance of common stock, shares \| shares	8,418,000
Issuance of common stock, per share price \| $ / shares	$ 14.00
Issuance of common stock, issuance costs \| $	$ 10,217,696

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:
Net (loss) income	$ (36,445)	$ (4,406)	$ (25,589)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	258	280	270
Non-cash interest expense	248	238	50
Amortization/accretion of premium/discount on investments	196	84	118
Loss on disposal of equipment	4
Share-based compensation costs	3,071	1,396	1,055
Deferred lease obligation	10		(4)
Fair value measurement of redeemable convertible preferred stock warrant liability	6,590	847	385
Net change in:
Accounts receivable	535	3,404	(4,187)
Prepaid and other current assets and deposits	(1,790)	65	(442)
Accounts payable and accrued liabilities	1,764	(3,784)	2,065
Net cash used in operating activities	(25,559)	(1,876)	(26,279)
Investing Activities:
Purchase of property and equipment	(193)	(126)	(321)
Purchase of short-term investments	(1,852)	(9,907)	(13,640)
Sales of short-term investments	750		500
Maturities of short-term investments	10,757	5,894	7,100
Repayment of loan to officer			125
Net cash provided by (used in) investing activities	9,462	(4,139)	(6,236)
Financing Activities:
Proceeds from issuance of redeemable convertible preferred stock and warrants			45,000
Proceeds from exercise of stock options	1,946	14	30
Proceeds from exercise of warrants	1,537
Proceeds from loan payable		15,000
Proceeds from initial public offering, net of offering costs	107,634
Debt discount		(75)
Repayment of loan payable	(4,950)	(2,601)	(1,965)
Stock offering and deferred financing costs		(24)	(249)
Net cash provided by financing activities	106,167	12,314	42,816
Increase in cash and cash equivalents	90,070	6,299	10,301
Cash and cash equivalents, beginning of period	19,906	13,607	3,306
Cash and cash equivalents, end of period	109,976	19,906	13,607
Supplemental cash flow information:
Interest payments	$ 1,092	$ 448	$ 186

The Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2013

The Business and Summary of Significant Accounting Policies [Abstract]

The Business and Summary of Significant Accounting Policies

1. The Business and Summary of Significant Accounting Policies

Description of Business

Chimerix is a biopharmaceutical company dedicated to discovering, developing and commercializing novel, oral antivirals to address unmet medical needs. The Company was founded in 2000 based on the promise of its proprietary lipid technology to unlock the potential of some of the most potent antivirals by enhancing their antiviral activity and safety profiles in convenient, orally administered dosing regiments. Based on the Company’s lipid technology, its lead compound, brincidofovir (CMX001) is in Phase 3 clinical development, its second compound, CMX157, was licensed to Merck after completing a Phase 1 study and the Company has an active discovery program focusing on viral targets for which no therapies are currently available.

On March 25, 2013, the Company’s board of directors approved and implemented a 3.55-for-1 reverse stock split of the Company’s outstanding common stock. The reverse stock split resulted in an adjustment to the preferred stock conversion price to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented.

On April 10, 2013, the Company completed the initial public offering (IPO) of its common stock pursuant to a registration statement on Form S-1. In the IPO, the Company sold an aggregate of 7,320,000 shares of common stock under the registration statement at a public offering price of $14.00 per share. Net proceeds were approximately $93.3 million, after deducting underwriting discounts and commissions of $7.1 million and offering expenses of $2.1 million. Upon the completion of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock and dividends accrued on Series F redeemable convertible preferred stock were converted into 15,556,091 shares of common stock and all outstanding warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase 1,613,395 shares of common stock. On April 16, 2013, the underwriters exercised the full over-allotment option pursuant to which the Company sold an additional 1,098,000 shares at $14.00 per share. Net proceeds from the over-allotment shares were approximately $14.3 million after deducting underwriting discounts and commissions of $1.1 million.

On October 23, 2013, the Company completed an underwritten secondary public offering of 2,476,995 shares of common stock held by certain of the Company’s existing stockholders. The Company did not issue any shares of common stock and received no proceeds in connection with such offering. The principal purposes of the offering were to facilitate an orderly distribution of shares and to increase the Company’s public float.

The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The preparation of the Company’s financial statements requires estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the financial statements and accompanying notes. Although these estimates are based on knowledge of current events and actions the Company may undertake in the future, actual results may ultimately differ from these estimates and assumptions.

Cash and Cash Equivalents

The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market accounts.

Investments

Investments consist primarily of corporate bonds and commercial paper. The Company invests in high-credit quality investments in accordance with its investment policy which minimizes the probability of loss.

Available-for-sale securities are carried at fair value as determined by quoted market prices, with the unrealized gains and losses, net of tax, reported as a separate component of stockholders deficit. Realized gains and losses are determined using the specific identification method and transactions are recorded on a settlement date basis in interest income or expense, net. Investments with original maturities beyond three months at the date of purchase and which mature on, or less than twelve months from, the balance sheet date are classified as long-term. The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Any such declines in value judged to be other-than-temporary on available-for-sale securities are reported in interest income or expense, net. There were no such declines in value for the years ended December 31, 2013 and 2012.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, short-term investments and accounts receivable. The Company is exposed to credit risk, subject to federal deposit insurance, in the event of default by the financial institutions holding its cash and cash equivalents to the extent of amounts recorded on the balance sheets. Accounts receivable represent amounts due from an agency of the federal government.

Accounts Receivable

Accounts receivable at December 31, 2013 and December 31, 2012 consisted of amounts billed and unbilled under the Company’s contract with the Biomedical Advanced Research and Development Authority (BARDA). Receivables under the BARDA contract are recorded as qualifying research activities as conducted and invoices from the Company’s vendors are received. The Company carries its accounts receivable at cost less an allowance for doubtful accounts. On a periodic basis, the Company evaluates its accounts receivable and establishes an allowance based on its history of collections and write-offs and the current status of all receivables. The Company does not accrue interest on trade receivables. If accounts become uncollectible, they will be written off through a charge to the allowance for doubtful accounts. The Company has not recorded a charge to allowance for doubtful accounts as management believes all receivables are fully collectible.

Fair Value of Financial Instruments

The carrying amounts of certain financial instruments, including accounts receivable, notes receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of such instruments. The carrying amount of borrowings under loans payable approximates its fair value based on the determination that the stated rate on such loans payable is consistent with current interest rates for similar borrowing arrangements available to the Company.

For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements, in accordance with the fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates and are often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, fair value measurements cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the calculated current or future fair values. The Company utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures.

The Company groups assets and liabilities at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. An adjustment to the pricing method used within either Level 1 or Level 2 inputs could generate a fair value measurement that effectively falls in a lower level in the hierarchy. These levels are:

Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.

Level 2 — Valuations based on quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and models for which all significant inputs are observable, either directly or indirectly.

Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.

The determination of where an asset or liability falls in the hierarchy requires significant judgment. The Company evaluates hierarchy disclosures and, based on various factors, it is possible that an asset or liability may be classified differently from period to period. However, the Company expects that changes in classification between levels will be rare.

The Company has cash equivalents, consisting of money market accounts and commercial paper, whose value is based on using quoted market prices. Accordingly, these securities are classified as Level 1.

At December 31, 2012, the Company had short-term investments, comprised of corporate bonds and commercial paper, for which quoted prices are not available that were valued using independent pricing models or other model-based valuation techniques such as the present value of future cash flows, adjusted for the security’s credit rating, prepayment assumptions and other factors such as credit loss assumptions. Accordingly, these securities are classified as Level 2.

The warrants issued for Series F redeemable convertible preferred stock included in the Company’s 2012 financial statements are categorized as Level 3 as there are significant unobservable inputs. The valuation of the warrants at December 31, 2012 reflected a two stage process. Using a contingent claims model in combination with the Company’s Series F financing, which occurred in February 2011, the fair value of total equity and all components of the Company’s capital structure, including the warrants, was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities consistent with market practice, a distribution of equity values was produced which covered the range of values that an informed market participant might expect. These outcomes were organized into ranges and a probability calculated based on the percent of the total falling into each range. This process created a range of equity values. Using a contingent claims framework, each equity value was allocated to the various components of the capital structure including the warrants. Each warrant value was weighted by its respective probability to determine the final fair value of the warrants as of December 31, 2012. The key unobservable inputs used in the determination of the fair value were (i) volatility – 79%, (ii) range of implied fair value of the Series F redeemable convertible preferred stock – $2.19 to $2.85, (iii) time to liquidity – 8 months to 5 years, and (iv) range of probabilities of liquidity event outcomes – 2% to 31%. The warrants were valued again at April 10, 2013, just prior to the Company’s IPO, using a Black-Scholes valuation model. The key unobservable inputs used in determination of the fair value at that time were (i) volatility – 79%, (ii) fair value of the Series F redeemable convertible preferred stock – $3.94, (iii) expected life – 2.5 years, (iv) risk-free interest rate – 0.24%, and (v) dividend yield – 0%. As the warrants for Series F redeemable convertible preferred stock converted to warrants for common stock upon the IPO, no future valuations are necessary.

There was no material re-measurement to fair value of financial assets and liabilities that are not measured at fair value on a recurring basis.

Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:


			Fair Value Measurements at
			December 31, 2013
	December 31, 2013		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	107,349	$	107,349	$	—	$	—


			Fair Value Measurements at December 31, 2012
	December 31, 2012		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	17,687	$	16,381	$	1,306	$	—
Short-term investments		9,849		—		9,849		—
Redeemable convertible preferred stock warrant liability		7,512		—		—		7,512

Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):


	Fair Value Measurements (Level 3)
	(in thousands)
Redeemable Convertible Preferred Stock Warrant Liability
Balance at January 1, 2012	$	6,491
Issuance		174
Fair value increase recorded in other expense		847
Fair value at December 31, 2012		7,512
Fair value increase recorded in other expense		6,590
Reclassification of warrant liability to additional paid-in capital		(14,102	)
Fair value at December 31, 2013	$	—

Prepaid and Other Current Assets

Prepaid and other current assets consist of the following:


	December 31, 2013		December 31, 2012
	(in thousands)
Prepaid development expenses	$	2,433	$	486
Deferred public offering costs		—		273
Other prepaid and other current assets		332		224
	$	2,765	$	983

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Depreciation is determined on a straight-line basis over the estimated useful lives of the assets, which generally range from three to five years. Leasehold improvements are amortized over the shorter of the useful life of the asset or the term of the related lease. Maintenance and repairs are charged against expense as incurred.

Impairment of Long-Lived Assets

The Company evaluates long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If the estimated future cash flows (undiscounted and without interest charges) from the use of an asset are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. To date, no such write-downs have occurred.

Deferred Public Offering Costs

Deferred public offering costs totaling $0.3 million at December 31, 2012 are included in prepaid and other current assets. These costs represent legal and accounting costs related to the Company’s efforts to raise capital through an IPO. At the completion of the IPO in April 2013, these costs were reclassified to additional paid-in capital as a reduction of the IPO proceeds.

Deferred Rent

The Company recognizes rent expense on a straight-line basis over the non-cancelable term of its operating lease and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. The Company also records landlord-funded lease incentives, such as reimbursable leasehold improvements, as a deferred rent liability, which is amortized as a reduction of rent expense over the non-cancelable term of its operating lease.

Accrued Liabilities

Accrued liabilities consist of the following:


	December 31, 2013		December 31, 2012
	(in thousands)
Accrued compensation	$	1,779	$	560
Accrued development expenses		350		98
Other accrued liabilities		291		248
	$	2,420	$	906

Redeemable Convertible Preferred Stock Warrant Liability

Freestanding warrants for shares that are either putable or redeemable are classified as liabilities on the balance sheet at fair value. As further discussed in Note 6, the preferred stock underlying certain warrants was redeemable in certain circumstances, and as such the freestanding warrants that are related to the purchase of the Company’s Series F preferred stock were liabilities that should be recorded at the estimated fair value. At the end of each reporting period, changes in the estimated fair value during the period are recorded in other income.

Redeemable Convertible Preferred Stock

The Company classified its redeemable convertible preferred stock, for which the Company did not control the redemption, outside of permanent equity. The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any offering costs, and the carrying value was adjusted to the redemption value at the end of each reporting period. These adjustments were effected through charges against additional paid-in capital and accumulated deficit.

Revenue Recognition

The Company’s revenues generally consist of (i) contract and grant revenues – revenues generated under federal contracts and other awarded grants, and (ii) collaboration and licensing revenues – revenues related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenues are recognized when the following criteria are met: (1) persuasive evidence that an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured.

For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively.

Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of the Company’s substantive performance obligations. If the Company does not have substantive performance obligations, the Company recognizes non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation.

Milestone payments are recognized when earned, provided that (i) the milestone event is substantive; (ii) there is no ongoing performance obligation related to the achievement of the milestone earned; and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement; and the related risk associated with the achievement of the milestone. Contingent based event payments the Company may receive under a license or collaboration agreement will be recognized when received.

For the years ended December 31, 2013, 2012 and 2011, contract and grant revenue consisted only of revenue from the BARDA contract as there was no grant revenue. The Company recognizes contract and grant revenue as qualifying research activities are conducted based on invoices received from the Company’s vendors. Changes in fringe and indirect rates are recognized as a change in estimate in the period such rate changes are approved by BARDA.

Clinical Trial Accruals

As part of the process of preparing financial statements, the Company is required to estimate its expenses resulting from its obligation under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate clinical trial expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of trials, or the services completed. During the course of a clinical trial, the Company adjusts its rate of clinical trial expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through December 31, 2013, there had been no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. The Company’s clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.

Research and Development

Major components of research and development costs include cash compensation, stock based compensation, pre-clinical studies, clinical trial and related clinical manufacturing, drug development, materials and supplies, legal, regulatory compliance, and fees paid to consultants and other entities that conduct certain research and development activities on the Company’s behalf. Research and development costs, including upfront fees and milestones paid to contract research organizations, are expensed as goods as received or services rendered. Costs incurred in connection with clinical trial activities for which the underlying nature of the activities themselves do not directly relate to active research and development, such as costs incurred for market research and focus groups linked to clinical strategy as well as costs to build the Company’s brand, are not included in research and development costs but are reflected as general and administrative costs.

Interest Expense, Net

Interest expense, net includes interest earned on short-term investments, interest incurred on loans payable, the amortization of deferred financing costs related to fees paid to attorneys and other non-lender entities in order to acquire debt, and the amortization of debt discount related to fees paid to the lender in order to acquire debt.

Income Taxes

Deferred tax assets and liabilities are determined based on differences between the financial and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are established when the Company determines that it is more likely than not that some portion of a deferred tax asset will not be realized. The Company has incurred operating losses from April 7, 2000 (inception) through December 31, 2013, and therefore has not recorded any current provision for income taxes.

Additionally, the Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefit recognized in the financial statements for a particular tax position is based on the largest benefit that is more likely than not to be realized upon settlement. Accordingly, the Company establishes reserves for uncertain tax positions.

Share-Based Compensation

The Company measures and recognizes compensation expense for all share-based payment awards made to employees and directors, including employee stock options, based on estimated fair values. The fair value of share-based awards is estimated on the grant date using the Black-Scholes valuation model. The value of the portion of the award that is ultimately expected to vest is recorded as expense over the requisite service periods.

The Company also accounts for equity instruments issued to non-employees using a fair value approach. The Company values equity instruments, stock options and warrants granted to lenders and consultants using the Black-Scholes valuation model. The measurement of non-employee share-based compensation is subject to periodic adjustments as the underlying equity instruments vest and is recognized as an expense over the term of the related financing or the period over which services are received.

Basic and Dilutive Net Loss Per Share of Common Stock

Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of converting redeemable convertible preferred stock, warrants to purchase redeemable convertible preferred stock and common stock, restricted stock and options. Diluted net loss per share of common stock is computed by dividing net loss by the sum of the weighted-average number of shares of common stock outstanding during the period plus the potential dilutive effects of redeemable convertible preferred stock and warrants to purchase redeemable convertible preferred stock, and options outstanding during the period calculated in accordance with the treasury stock method, but are excluded if their effect is anti-dilutive. Because the impact of these items is anti-dilutive during the periods of net loss, there was no difference between basic and diluted loss per share of common stock at December 31, 2013, 2012 and 2011.

The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of converting redeemable convertible preferred stock, warrants to purchase convertible preferred stock and options to purchase common stock, as the impact of such items are anti-dilutive during periods of net loss. Shares excluded from the calculations were 4,773,213, 11,259,579 and 11,034,134 for the years ended December 31, 2013, 2012 and 2011, respectively.

Segments

The Company operates in only one segment. The chief operating decision-maker, who is the Company’s Chief Executive Officer, and management use cash flows as the primary measure to manage the business and do not segment the business for internal reporting or decision making.

Impact of Recently Issued Accounting Standards

In July of 2013, the Financial Accounting Standards Board issued ASU 2013-11, “Income Taxes, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (a consensus of the FASB Emerging Issues Taskforce)” ("ASU 2013-11"). Beginning January 1, 2014, the effective date of this regulation, the Company will adopt the provisions of ASU 2013-11 related to presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. Adoption of ASU 2013-11 is not expected to have a material impact to the financial statements.

Investments

12 Months Ended

Dec. 31, 2013

Investments [Abstract]

Investments

2. Investments

The Company had no short or long-term investments at December 31, 2013.

The following table summarizes available-for-sale securities as of December 31, 2012:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Corporate bonds	$	8,353	$	—	$	(2	)	$	8,351
Commercial paper		1,498		—		—			1,498
Total	$	9,851	$	—	$	(2	)	$	9,849

All of the Company’s investments as of December 31, 2012 had maturities of one year or less.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-Glossary Debt Security
-URI http://asc.fasb.org/extlink&oid=6509901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-Glossary Equity Security
-URI http://asc.fasb.org/extlink&oid=6511694

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27405-111563

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 3, 19, 20, 21, 22, 137
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Property and Equipment

12 Months Ended

Dec. 31, 2013

Property and Equipment [Abstract]

Property and Equipment

3. Property and Equipment

Property and equipment consist of the following:


	December 31, 2013			December 31, 2012
	(in thousands)
Lab equipment	$	873		$	958
Leasehold improvements		78			78
Computer equipment		324			393
Office furniture and equipment		222			212
		1,497			1,641
Less accumulated depreciation		(1,159	)		(1,234	)
	$	338		$	407

- Definition

The entire disclosure for long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software. This disclosure may include property plant and equipment accounting policies and methodology, a schedule of property, plant and equipment gross, additions, deletions, transfers and other changes, depreciation, depletion and amortization expense, net, accumulated depreciation, depletion and amortization expense and useful lives, income statement disclosures, assets held for sale and public utility disclosures.

+ References + Details

Loan Payable

12 Months Ended

Dec. 31, 2013

Loan Payable [Abstract]

Loan Payable

4. Loan Payable

On January 27, 2012, the Company entered into a Loan and Security Agreement (LSA) with Silicon Valley Bank (SVB) and MidCap Financial SBIC, LP (MidCap) allowing for borrowings up to $15.0 million, split between a first tranche of $3.0 million borrowed at the time of the agreement, and a second tranche of up to $12.0 million that would be available to be drawn by December 31, 2012 upon meeting one of three stated financial and/or operational goals.

The first tranche was used to repay the remaining principal balance outstanding of $2.6 million under a previous loan. This repayment was deemed a modification of debt and therefore the remaining related deferred financing costs totaling $0.1 million remained in deferred financing costs and are being amortized over the term of the LSA through interest expense. The first tranche has an interest-only period of twelve months followed by a 30-month principal and interest amortization period with interest being charged at 8.25% per year for the full period of the LSA.

The Company met one of the financial and/or operational goals mentioned above and, in September 2012, the remaining $12.0 million was borrowed in the second tranche. The second tranche has a six-month interest-only period followed by a 32 month principal and interest amortization period with interest being charged at the same rate as the first tranche. There are certain fees in accordance with the LSA which are being recorded as discounts or other long and short-term liabilities depending on the nature of the fees. The fees are being accreted through interest expense. Approximately $0.1 million and $0.1 million was included in interest expense for the years ended December 31, 2013 and 2012, respectively.

Concurrently with entering into the LSA, the Company also granted SVB a warrant to purchase shares of Series F preferred stock at a price of $2.045 per share equal to 2% of the aggregate amount of the advances made to the Company pursuant to the LSA, divided by the exercise price. In relation to the first tranche, the warrant became exercisable to purchase an aggregate of 29,340 shares of Series F preferred stock, and in relation to the second tranche, the warrant became exercisable to purchase an additional 117,360 shares of Series F preferred stock. As discussed in Note 1, the warrant is classified as a liability and is required to be measured at fair value. Therefore, the warrant was recorded as a debt discount at its fair value at the time of grant and accreted over the life of the LSA using the effective interest method. Upon the completion of the Company’s IPO, this warrant was converted into a warrant to purchase 41,323 shares of common stock at an exercise price equal to $7.26. In May 2013, SVB exercised the warrant in full and it is no longer outstanding.

The future payments under the LSA are as follows (in thousands):



Years ending December 31,
2014	$	6,322
2015		4,508
		10,830
Less: amount representing interest		(780	)
Total payments under LSA	$	10,050

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References + Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2013

Commitments and Contingencies [Abstract]

Commitments and Contingencies

5. Commitments and Contingencies

Leases

The Company leases its facilities and certain office equipment under long-term non-cancelable operating leases that expire at various dates through 2018. The Company has the following minimum payments under noncancelable operating lease obligations that existed at December 31, 2013 (in thousands):



Years ending December 31,
2014	$	331
2015		275
2016		245
2017		243
2018		41
	$	1,135

Rent expense under non-cancelable operating leases and other month-to-month equipment rental agreements, including common area maintenance fees, totaled approximately $0.5 million and $0.4 million for the years ended December 31, 2013 and 2012, respectively.

Significance of Revenue Source

The Company is the recipient of federal research contract funds from BARDA. Periodic audits are required under the grant and contract agreements and certain costs may be questioned as appropriate under the agreements. Management believes that such amounts in the current year, if any, are not significant. Accordingly, no provision for refundable amounts under the agreements has been made as of December 31, 2013 and 2012.

- Definition

The entire disclosure for commitments and contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6449706&loc=d3e16207-108621

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14435-108349

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.25)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25287-109308

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Interpretation (FIN)
-Number 14
-Paragraph 3
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 9, 10, 11, 12
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2013

Redeemable Convertible Preferred Stock [Abstract]

Redeemable Convertible Preferred Stock

6. Redeemable Convertible Preferred Stock

In February 2011, the Company issued 22,004,895 shares of $0.001 par value Series F redeemable convertible preferred stock at $2.045 per share and warrants to purchase an aggregate of 5,501,215 shares of Series F redeemable convertible preferred stock at an exercise price of $2.045 per share for proceeds of $45.0 million, less issuance costs of $0.2 million. Upon the completion of the Company’s IPO, these warrants were converted into warrants to purchase an aggregate of 1,549,628 shares of common stock at an exercise price of $7.26 per share. The warrants are exercisable at any time and expire on February 4, 2018.

In January 2012, the Company issued a warrant to SVB to purchase a number of shares of Series F redeemable convertible preferred stock at an exercise price of $2.045 per share equal to 2% of the aggregate amount of the advances made to the Company pursuant to the LSA, divided by the exercise price. Following the first and second tranches of the LSA, the warrant was exercisable to purchase an aggregate of 146,700 shares of Series F redeemable convertible preferred stock. Upon the completion of the Company’s IPO, this warrant was converted into a warrant to purchase 41,323 shares of common stock at an exercise price of $7.26 per share. In May 2013, SVB exercised the warrant in full and it is no longer outstanding.

The following table summarizes the authorized, issued and outstanding shares of redeemable convertible preferred stock as of December 31, 2012:


	Authorized Shares		Issued and Outstanding Shares
Series A		800,000		800,000
Series B		2,233,879		2,233,879
Series B-1		2,054,333		2,033,333
Series C		5,141,690		5,141,690
Series D		11,354,526		11,295,846
Series E		7,894,871		7,894,871
Series F		40,200,000		22,004,895
Total Shares		69,679,299		51,404,514

Upon the completion of the Company’s IPO in April 2013, the Company’s outstanding shares of redeemable convertible preferred stock and dividends accrued on Series F redeemable convertible preferred stock were automatically converted into an aggregate of 15,556,091 shares of common stock.

Warrants

The following warrants for the purchase of preferred stock were issued, outstanding and exercisable at December 31, 2012:


Class	Date	Shares		Price Per Share		Expiration
Series B-1	November 5, 2003		21,000	$	1.500	November 2013
Series D	November 24, 2008		58,680	$	2.045	November 2018
Series F	February 7, 2011		5,501,215	$	2.045	February 2018
Series F	January 27, 2012		146,700	$	2.045	January 2022

As discussed in Note 1, the warrants exercisable for the Company’s Series F preferred stock were classified as a liability and were required to be measured at fair value. Therefore, such warrants were recorded at the full fair value with the Company’s Series F preferred stock being recorded at the residual value at the time of issuance. At each reporting date prior to the Company’s IPO, the warrants exercisable for the Company’s Series F preferred stock were recorded to fair value which was charged to other income. For the years ended December 31, 2013 and 2012, the Company recorded expense of $6.4 million and $0.8 million, respectively, related to the valuation of the warrants. These amounts, coupled with the fair valuation of the warrants issued in relation to the Company’s LSA (see note 4), total to the fair value adjustments to warrant liability amount per the statements of operations and comprehensive loss.

Upon the completion of the Company’s IPO, all outstanding warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase 1,613,395 shares of common stock and are no longer required to be measured at fair value. On April 16, 2013, a warrant was exercised to purchase 211,783 shares of the Company’s common stock. The Company received proceeds of $1.5 million in connection with such exercise. On May 24, 2013, a warrant was net exercised which resulted in the issuance of 37,600 shares of the Company’s common stock. On November 5, 2013, a warrant was net exercised which resulted in the issuance of 3,906 shares of the Company’s common stock.

The following warrants for the purchase of common stock were issued, outstanding and exercisable at December 31, 2013:

Class

Date

Price Per Share

Expiration

Common

February 7, 2011

1,337,845

7.26

February 2018

Stockholders' Equity (Deficit)

12 Months Ended

Dec. 31, 2013

Stockholders' Equity (Deficit) [Abstract]

Stockholders' Equity (Deficit)

7. Stockholders’ Equity (Deficit)

Common Stock

The Company’s common stock consists of 200.0 million and 89.7 million authorized shares at December 31, 2013 and December 31, 2012, respectively, and 26.7 million and 1.5 million shares issued and outstanding at December 31, 2013 and December 31, 2012, respectively.

Shares Reserved for Future Issuance

The following shares of common stock reserved for future issuances:


	December 31, 2013		December 31, 2012

Conversion of preferred stock and preferred stock warrants		—		16,093,483
Exercise of common stock warrants		1,337,845		—
Stock options issued and outstanding		1,946,823		2,593,423
Restricted Stock units outstanding		-		43,199
Authorized for future purchases under the 2013 Employee Stock Purchase Plan		704,225		—
Authorized for future grants under the 2013 Equity Incentive Plan		1,681,932		—
Authorized for future grants under the 2012 Equity Incentive Plan		—		427,933
		5,670,825		19,158,038

Stock Options

In connection with the Company’s IPO, the Company adopted the 2013 Equity Incentive Plan (the 2013 Plan). The 2013 Plan provides for the grant of incentive stock options (ISOs), nonstatutory stock options (NSOs), stock appreciation rights, restricted stock awards, restricted stock unit (RSU) awards, performance-based stock awards, and other forms of equity compensation (collectively, stock awards), all of which may be granted to employees, including officers, non-employee directors and consultants of the Company and its affiliates. Additionally, the 2013 Plan provides for the grant of performance cash awards. ISOs may be granted only to employees. All other awards may be granted to employees, including officers, and to non-employee directors and consultants. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (i) 1,408,450 shares, plus (ii) 244,717 shares, which was the number of shares reserved for issuance under the Company’s 2012 Equity Incentive Plan (the 2012 Plan) at the time the 2013 Plan became effective, plus (iii) any shares subject to outstanding stock options or other stock awards that would have otherwise returned to the 2012 Plan (such as upon the expiration or termination of a stock award prior to vesting). Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2014 and continuing through and including January 1, 2023, by 2.5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. The maximum number of shares that may be issued upon the exercise of ISOs under the 2013 Plan is 2,816,901 shares. Following the effectiveness of the 2013 Plan in April 2013, no further grants were made under the 2012 Plan.

The 2013 Plan has an “early exercise” provision under which options to purchase common stock may be exercised prior to being fully vested; however, the shares issued for options exercised under the “early exercise” provision continue to vest under the same terms as the underlying exercised option. Upon termination of an employee prior to the vesting of such shares, the Company can either repurchase the unvested shares or let the repurchase right expire.

The Company estimates the fair value of its share-based awards to employees, directors and consultants using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of highly complex and subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the Company’s limited operating history and historical and implied volatility data, the Company has based its estimates of expected volatility on a blend of Company specific historical data and a group of similar public traded companies. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, positions within the industry, and with historical share price information sufficient to meet the expected life of its stock options. For employee stock options the Company uses the “simplified” method for estimating expected life, whereby, the expected life equals the arithmetic average of the vesting term and the original contractual term of the option due to its lack of sufficient historical data. The expected term for share-based compensation granted to non-employees is the contractual life. The risk-free interest rates for the periods within the expected life of the option are based on the U.S. Treasury instrument with a life that is similar to the expected life of the option grant. The Company has never paid, and does not expect to pay, dividends in the foreseeable future. The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the options granted.


	Employees
	Year Ended December 31,
	2013			2012			2011
Dividend yield		0.00	%		0.00	%		0.00	%
Weighted-average risk-free interest rate		1.49	%		0.86	%		2.85	%
Volatility		76.40	%		80.55	%		82.00	%
Expected term (in years)		6.1			6.0			7.0
Weighted-average fair value per option	$	2.52		$	1.93		$	1.74


			Non-Employees
			Year Ended December 31,
	2013					2012			2011
Dividend yield				0.00	%		0.00	%		0.00	%
Weighted-average risk-free interest rate				1.30	%		0.78	%		0.40	%
Volatility				79.69	%		81.77	%		77.80	%
Expected term (in years)				6.2			5.8			2.7
Weighted-average fair value per option		$		5.01		$	3.48		$	3.38

The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised. For the years ended December 31, 2013, 2012 and 2011, the Company applied a forfeiture rate based on the Company’s historical forfeitures.

In February 2013, the Company’s board of directors adopted the 2013 Employee Stock Purchase Plan (ESPP), which was subsequently ratified by stockholders and became effective in April 2013. The purpose of the ESPP is to retain the services of new employees and secure the services of new and existing employees while providing incentives for such individuals to exert maximum efforts toward the Company’s success and that of its affiliates. The ESPP initially authorized the issuance of 704,225 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of its designated affiliates. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2014 through January 1, 2023 by the least of (a) 1% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (b) 422,535 shares, or (c) a number determined by the Company’s board of directors that is less than (a) and (b). The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code of 1986. As of the date hereof, no shares of common stock have been purchased under the ESPP.

A summary of activity related to the Company’s stock options is as follows:


	Number of Options Outstanding			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (in Years)
Balance, January 1, 2012		2,631,415		$	2.24		7.69
Granted		382,167			3.24		—
Exercised		(16,530	)		0.82		—
Expired or Canceled		(102,228	)		2.63		—
Forfeited		(301,401	)		1.69		—
Balance, December 31, 2012		2,593,423		$	2.45		7.36
Granted		292,906			10.62		—
Exercised		(801,049	)		2.43		—
Expired or Canceled		(2,816	)		1.57		—
Forfeited		(135,641	)		4.55		—
Balance, December 31, 2013		1,946,823		$	3.54		7.03
Exercisable at December 31, 2013		1,266,070		$	2.32		6.21
Vested or expected to vest at December 31, 2013		1,952,222		$	3.50		7.02

At December 31, 2013, the aggregate intrinsic value of options outstanding and exercisable was $16.2 million. The total intrinsic value of options exercised was $12.4 million, $18,000 and $16,000 for the years ended December 31, 2013, 2012 and 2011, respectively.

In 2012, the Company modified option grants for four individuals. Three of the modifications extended the term to exercise the option resulting in $30,000 in additional compensation expense. One option was modified to continue vesting after the participant’s termination and to extend the time to exercise such option resulting in additional compensation expense of $0.3 million.

For awards with only service conditions and graded-vesting features, the Company recognizes compensation expense on a straight-line basis over the requisite service period. The fair value of options vested and share-based compensation expense recognized are as follows:

	Year Ended December 31,
	2013		2012		2011
	(in thousands)
Research and development:
Employee	$	537	$	336	$	315
Non-employee		67		80		—
General and administrative:
Employee		458		921		651
Non-employee		82		59		—
	$	1,144	$	1,396	$	966

Cash received from option exercises under all share-based payment arrangements for 2013 and 2012, was $1.9 million and $14,000, respectively. There was no actual tax benefit realized for the tax deductions from option exercises of the share-based payment arrangements during 2013 or 2012.

As of December 31, 2013, there was approximately $2.5 million of total unrecognized compensation cost related to non-vested share-based compensation arrangements granted under the 2013 Plan. That compensation cost is expected to be recognized over a weighted-average period of approximately 2.54 years.

The Company continues to account for stock options issued to non-employees using a fair value approach. The compensation costs of these arrangements are subject to re-measurement over the vesting terms as earned. Compensation cost for performance-based awards is recognized when it is probable that the performance criteria will be met.

Restricted Stock Units

In 2013 and 2012, the Company issued RSUs to certain employees which vest based on specific performance criteria. By their terms, the RSUs became immediately vested upon the effective date of the registration statement for the Company’s common stock in connection with the IPO, subject to the continuous service with the Company at the vesting event. When vested, the RSU represented the right to be issued the number of shares of the Company’s common stock that is equal to the number of RSUs granted.

A summary of activity related to the Company’s RSUs is as follows:


	Number of Restricted Stock Units Outstanding
Balance, December 31, 2012		43,199
Granted		59,348
Share issuance		(102,547	)
Balance, December 31, 2013		—

In April 2013, $1.9 million in compensation expense had been recorded in connection with the RSUs as the performance criterion was met upon the completion of the Company’s IPO. In November 2013, the requisite number of shares of common stock were issued in relation to the RSUs.

Fair Value Estimate

Prior to the Company’s IPO, the Company was required to estimate the fair value of the common stock underlying stock-based awards when performing the fair value calculations with the Black-Scholes option-pricing model. The fair value of the common stock underlying stock-based awards was determined on each grant date by the Company’s board of directors, with input from management. All options to purchase shares of common stock are intended to be granted with an exercise price per share no less than the fair value per share of common stock underlying those options on the date of grant, based on the information known on the date of grant.

The Company was privately held with no active public market for its common stock. Therefore, management had for financial reporting purposes periodically determined the estimated per share fair value of the Company’s common stock and redeemable convertible preferred stock at various dates using contemporaneous valuations consistent with the American Institute of Certified Public Accountants Practice Aid, “Valuation of Privately-Held Company Equity Securities Issued as Compensation,” also known as the Practice Aid. These valuations were performed with the assistance of a third-party valuation specialist. The Company performed these contemporaneous valuations as of February 15, 2011, December 31, 2011, and September 30, 2012 and December 31, 2012. In conducting these contemporaneous valuations, management considered all objective and subjective factors that it believed to be relevant in each valuation conducted, including management’s best estimate of the Company’s business condition, prospects and operating performance at each valuation date. Within the contemporaneous valuations performed, a range of factors, assumptions and methodologies were used. The significant factors included external market conditions affecting the biotechnology industry, trends within the biotechnology industry, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of the preferred stock relative to common stock at the time of each grant, the results of operations, financial position, status of research and development efforts, stage of development and business strategy, the lack of an active public market for the common and preferred stock, and the likelihood of achieving a liquidity event such as an IPO or sale of the Company in light of prevailing market conditions.

The dates of the Company’s contemporaneous valuations had not always coincided with the dates of its stock-based compensation grants. In such instances, management’s estimates had been based on the most recent contemporaneous valuation of the Company’s shares of common stock and its assessment of additional objective and subjective factors management believed were relevant and which may have changed from the date of the most recent contemporaneous valuation through the date of the grant. In addition, the Company performed retrospective valuations as of certain key option grant dates using similar methodologies as were used in the contemporaneous valuations. As a result, the Company concluded certain options granted in 2012 had reassessed values different from the grant date. The reassessed values were used to determine stock compensation expense for the year ended December 31, 2012.

- Definition

The entire disclosure for shareholders' equity, comprised of portions attributable to the parent entity and noncontrolling interest, if any, including other comprehensive income (as applicable). Including, but not limited to: (1) balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings; (2) accumulated balance for each classification of other comprehensive income and total amount of comprehensive income; (3) amount and nature of changes in separate accounts, including the number of shares authorized and outstanding, number of shares issued upon exercise and conversion, and for other comprehensive income, the adjustments for reclassifications to net income; (4) rights and privileges of each class of stock authorized; (5) basis of treasury stock, if other than cost, and amounts paid and accounting treatment for treasury stock purchased significantly in excess of market; (6) dividends paid or payable per share and in the aggregate for each class of stock for each period presented; (7) dividend restrictions and accumulated preferred dividends in arrears (in aggregate and per share amount); (8) retained earnings appropriations or restrictions, such as dividend restrictions; (9) impact of change in accounting principle, initial adoption of new accounting principle and correction of an error in previously issued financial statements; (10) shares held in trust for Employee Stock Ownership Plan (ESOP); (11) deferred compensation related to issuance of capital stock; (12) note received for issuance of stock; (13) unamortized discount on shares; (14) description, terms, and number of warrants or rights outstanding; (15) shares under subscription and subscription receivables, effective date of new retained earnings after quasi-reorganization and deficit eliminated by quasi-reorganization and, for a period of at least ten years after the effective date, the point in time from which the new retained dates; and (16) retroactive effective of subsequent change in capital structure.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 4.E)
-URI http://asc.fasb.org/extlink&oid=6228006&loc=d3e74512-122707

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29-31)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB TOPIC 4.C)
-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187143-122770

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Section B
-Paragraph 7, 11A
-Chapter 1
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 16: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 15
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 17: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph d
-Article 4

Reference 18: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30, 31
-Article 5

Reference 19: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section E

Reference 20: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Article 4

Reference 21: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section C

Reference 22: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 129
-Paragraph 2, 3, 4, 5, 6, 7, 8
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 23: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

+ Details

Income Taxes

12 Months Ended

Dec. 31, 2013

Income Taxes [Abstract]

Income Taxes

8. Income Taxes

No income tax expense or benefit has been recorded for the years ended December 31, 2013 or December 31, 2012. This is due to the establishment of a valuation allowance against the deferred tax assets generated during those periods. At December 31, 2013, the Company has concluded that it is more likely than not that the Company may not realize the benefit of its deferred tax assets due to its history of losses. Accordingly, the net deferred tax assets have been fully reserved.

A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2013, 2012, and 2011:



	2013						2012						2011
	Amount			% of Pretax Earnings			Amount			% of Pretax Earnings			Amount			% of Pretax Earnings
	(in thousands)
Income tax benefit at statutory rate	$	(12,392	)		34.0	%	$	(1,499	)		34.0	%	$	(8,700	)		34.0	%
State income taxes		(852	)		2.3	%		(100	)		2.3	%		(1,164	)		4.6	%
Research and development credits		(2,265	)		6.2	%		—			0.0	%		(1,171	)		4.6	%
Permanent items		3,060			(8.4	)%		868			(19.7	)%		964			(3.8	)%
Provision to return adjustments		320			(0.9	)%		2			0.0	%		12			0.0	%
Effect of change in state tax rate		(1)			0.0	%		609			(13.9	)%		630			(2.5	)%
Increase in unrecognized tax benefits		566			(1.5	)%		—			0.0	%		314			(1.2	)%
Valuation allowance		11,564			(31.7	)%		120			(2.7	)%		9,115			(35.7	)%
Net benefit	$	—			0.0	%	$	—			0.0	%	$	—			0.0	%

The components of deferred tax assets and liabilities at December 31, 2013 and 2012 are as follows:



	December 31,
	2013			2012
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	40,721		$	31,431
Research and development expenses		127			34
Capitalized Section 174 expenses		69			80
Research and development credits		2,640			941
Accrued bonuses		405			54
Other		497			445
Total gross deferred tax assets		44,459			32,985
Valuation allowance		(44,405	)		(32,841	)
		54			144
Deferred tax liabilities:
Other		(54	)		(144	)
Total deferred tax liabilities		(54	)		(144	)
Net deferred tax assets	$	—		$	—

At December 31, 2013, the Company has net operating loss carryforwards for federal and state tax purposes of approximately $117.5 million and $106 million, respectively. At December 31, 2012, the Company has net operating loss carryforwards for federal and state purposes of approximately $83.6 million and $65.8 million, respectively. The federal losses begin to expire in 2020 and the state losses begin to expire in 2023. The Company’s federal and state net operating loss carryforwards include approximately $7.3 million of excess tax benefits related to deductions from the exercise of stock options. The tax benefit of these deductions has not been recognized in deferred tax assets. If utilized, the benefits from these deductions will be recorded as adjustments to additional paid-in capital. In addition, the Company has tax credit carryforwards for federal tax purposes of approximately $3.5 million as of December 31, 2013, which begin to expire in 2022. The future utilization of net operating loss and tax credit carryforwards may be limited due to changes in ownership. Management has recorded a valuation allowance for all of the deferred tax assets due to the uncertainty of future taxable income.

The research and development credit, which had previously expired on December 31, 2011, was reinstated as part of the American Taxpayer Relief Act of 2012 enacted on January 2, 2013. This legislation retroactively reinstated and extended the credit from the previous expiration date through December 31, 2013. As a result, the Company adjusted its deferred tax assets in 2013 for the 2013 and 2012 research and development credits, which resulted in an increase to the deferred tax assets and a corresponding increase to the valuation allowance of $1.2 million and $1.1 million, respectively.

In general, if the Company experiences a greater than 50% aggregate change in ownership of certain significant stockholders over a three-year period (a Section 382 ownership change), utilization of its pre-change net operating loss carryforwards is subject to an annual limitation under Section 382 of the Internal Revenue Code (and similar state laws). The annual limitation generally is determined by multiplying the value of the Company’s stock at the time of such ownership change (subject to certain adjustments) by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the net operating loss carryforwards before utilization and may be substantial. The ability of the Company to use its net operating loss carryforwards may be limited or lost if the Company experienced one or more Section 382 ownership changes in connection with past offerings of its stock or as a result of future changes in its stock ownership. Losses from a specific period may be subject to multiple limitations, and would generally be limited by the lowest of those limitations.

The Company has determined that a Section 382 ownership change occurred in 2002, and as such, losses incurred prior to that date are subject to an annual limitation of at least $64,000. Additionally, the Company has determined that a Section 382 ownership change occurred in 2007, and as such, losses incurred prior to that date are subject to an annual limitation of at least $762,000. The Company evaluated Section 382 ownership changes subsequent to 2007 through 2013 and concluded that a Section 382 ownership change occurred in 2013 as a result of the initial public offering, the Company’s most recent private placement and other transactions that have occurred since 2007. As such, losses incurred prior to that date are subject to an annual limitation of at least $6.7 million.

The Company had gross unrecognized tax benefits of approximately $0.3 million as of January 1, 2013. As the 2012 R&D tax credit was not yet enacted into current law, no R&D credit was reflected on the 2012 provision. As a result, the Company recognized an increase in the unrecognized tax benefit associated with the federal R&D credit carryover in the current year related to the periods ending December 31, 2012 and 2013. As of December 31, 2013, the total gross unrecognized tax benefits were approximately $0.9 million and of this total, none would reduce the Company’s effective tax rate if recognized. The Company does not anticipate a significant change in total unrecognized tax benefits or the Company’s effective tax rate due to the settlement of audits or the expiration of statutes of limitations within the next twelve months. Furthermore, the Company does not expect any cash settlement with the taxing authorities as a result of these unrecognized tax benefits as the Company has sufficient unutilized carryforward attributes to offset the tax impact of these adjustments.

The Company has determined that there may be a future limitation on the Company’s ability to utilize its entire federal R&D credit carryover. Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the year ended December 31, 2013, as follows (in thousands):



Balance at December 31, 2011	$	314
Increases related to 2012		—
Balance at December 31, 2012		314
Increase related to 2013		297
Increase related to prior periods		269
Balance at December 31, 2013	$	880

The Company has determined that it had no other material uncertain tax benefits for the year ended December 31, 2013. As of January 1, 2014, due to the carry forward of unutilized net operating losses and research and development credits, the Company is subject to U.S. Federal and state income tax examinations for the tax years 2000 through 2013. The Company recognizes accrued interest related to unrecognized tax benefits in interest expense and penalties in operating expense. No amounts were accrued for the payment of interest and penalties at January 1, 2014.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

+ Details

Significant Agreements	12 Months Ended
Significant Agreements	Dec. 31, 2013
Significant Agreements [Abstract]
Significant Agreements	9. Significant Agreements The Regents of the University of California In May 2002, the Company entered into a license agreement with The Regents of the University of California (UC) under which the Company obtained an exclusive, worldwide license to UC’s patent rights in certain inventions (the UC Patent Rights) related to lipid-conjugated antiviral compounds and their use, including certain patents relating to brincidofovir and CMX157. The license agreement was amended in September 2002 in order to expand the scope of the license and again in December 2010 in order to modify certain financial terms. The agreement was amended a third time in September 2011 to add additional patents related to certain metabolically stable lipid-conjugate compounds. A fourth amendment was executed in July 2012 to alter the rights and obligations of the parties in light of the Company’s current business plans. As partial consideration for the rights granted to the Company under the license agreement, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights. In connection with the development and commercialization of brincidofovir and CMX157, the Company could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement. Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UC Patent Rights for all human and veterinary uses, and to sublicense such rights. UC retained the right, on behalf of itself and other non-profit institutions, to use the UC Patent Rights for educational and research purposes and to publish information about the UC Patent Rights. In consideration for the rights granted under the license agreement, the Company has issued UC an aggregate of 64,788 shares of common stock. As additional consideration, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights, plus certain annual fees to maintain such patents until the Company commercializes a product utilizing UC Patent Rights. In addition, upon commercialization of any product utilizing the UC Patent Rights (which would include the commercialization of brincidofovir or CMX157), the Company will be required to pay low single digit royalties on net sales of such product. In the event the Company sublicenses a UC Patent Right the Company is obligated to pay to UC a fee, which amount will vary depending upon the size of any upfront payment the Company receives and the clinical development stage of the compound being sublicensed, but which could be up to approximately 50% of the sublicense fee in certain circumstances. With respect to brincidofovir or CMX157, the fee payable to UC will not exceed 5% and 10% of the sublicense fee, respectively. In addition, the Company will also be required to pay to UC a low single digit sublicense royalty on net sales of products that use the sublicensed UC Patent Rights, but in no event will the Company be required to pay more than 50% of the royalties it receives in connection with the relevant sublicense. Any such royalty payment will be reduced by other payments the Company is required to make to third parties until a minimum royalty has been reached. As a result of meeting certain milestones and sublicense fees related to this license agreement, the Company recognized expenses of $0.9 million for the year ended December 31, 2012. The Company did not recognize expenses under this license agreement for the year ended December 31, 2013. Biomedical Advanced Research and Development Authority (BARDA) In February 2011, the Company entered into a contract with BARDA for the advanced development of brincidofovir as a medical countermeasure in the event of a smallpox release. The contract has been amended several times; most recently on December 10, 2013 to increase the option segment award to $5.3 million. Under the contract, BARDA will reimburse the Company, plus pay a fixed fee, for the research and development of brincidofovir as a broad-spectrum therapeutic antiviral for the treatment of smallpox infections. The contract consists of an initial performance period, referred to as the base performance segment, plus up to four extension periods of approximately one year each, referred to as option segments, each of which may be exercised at BARDA’s sole discretion. The Company must complete the agreed upon milestones and deliverables in each discrete work segment before the next option segment is eligible to be exercised. Under the contract as currently in effect, the Company may receive up to $75.8 million in expense reimbursement and $5.3 million in fees. The Company is currently performing under the first option segment of the contract during which the Company may receive up to a total of $5.3 million in expense reimbursement and fees. The term of the first option segment is 12 months and is scheduled to end on May 30, 2014. Merck, Sharp & Dohme Corp. In July 2012, the Company entered into a collaboration and license agreement granting Merck exclusive worldwide rights to CMX157, the Company’s lipid acyclic nucleoside phosphonate currently being evaluated to treat HIV infection. Under the terms of the agreement, Merck received an exclusive worldwide license for any human use of CMX157 and has agreed to use commercially reasonable efforts to develop and commercialize CMX157 in the United States and at least three major European markets. Following execution of the agreement, the Company received a $17.5 million upfront payment from Merck. As additional consideration, the Company is eligible to receive up to a total of $151.0 million in milestone payments if certain development and regulatory milestones are achieved by Merck for products utilizing CMX157, as well as tiered royalties on net sales ranging from high single digits to low double digits, depending upon the volume of sales of each applicable product, if CMX157 is successfully commercialized. Milestone payments are triggered upon the completion of various stages of the regulatory approval process for each of the first two indications for CMX157, with the final milestones reached upon approval in the United States and three major European markets. Royalties for any given product will continue on a country-by-country basis through the later of the expiration of the Company’s patent rights applicable to such product or ten years from the first commercial sale of such product. The Company’s participation in the collaboration with Merck, including its involvement in the joint steering committee to monitor the development of CMX157, represents a right and an observation role only, rather than a substantive performance obligation. As such, the Company’s performance in this collaboration relates to the specific transfers in connection with the license which was completed during the same quarter the agreement was entered into. Therefore, the Company recognized the upfront payment during the year ended December 31, 2012. The contingent event-based payments that the Company may receive pursuant to the agreement do not meet the definition of a milestone as achievement of the triggering event for such payments is based on the performance of Merck and not the Company. Therefore, the milestone method will not be applied to those payments.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2013

Selected Quarterly Financial Information [Abstract]

Selected Quarterly Financial Data (Unaudited)

10. Selected Quarterly Financial Data (Unaudited)

The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2013 and 2012 are as follows (in thousands, except per share data):


	2013 Quarter
	Fourth		Third		Second		First

Total revenues	$	879	$	912	$	808	$	1,771
Operating loss		(7,979)		(6,436)		(7,656)		(6,548)
Net loss		(8,174)		(6,706)		(12,459)		(9,107)
Net loss per common share, basic and diluted	$	(0.31)	$	(0.26)	$	(0.91)	$	(22.58)
Weighted average shares outstanding, basic and diluted		26,416,787		25,866,109		23,067,201		1,534,016


	2012 Quarter
	Fourth		Third		Second		First

Total revenues	$	3,581	$	20,856	$	6,205	$	3,078
Operating (loss) income		(4,143)		11,272		(4,422)		(5,490)
Net (loss) income		(4,326)		11,142		(4,324)		(6,898)
Net (loss) income per common share, basic	$	(3.90)	$	6.70	$	(3.44)	$	(5.14)
Net (loss) income per common share, diluted	$	(3.90)	$	0.11	$	(3.44)	$	(5.14)
Weighted average shares outstanding, basic		1,532,633		1,529,442		1,518,753		1,517,465
Weighted average shares outstanding, diluted		1,532,633		52,933,956		1,518,753		1,517,465

Net income (loss) per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation. Diluted weighted average shares outstanding are identical to basic weighted average shares outstanding and diluted net loss per common share is identical to basic net loss per common share for all quarters of 2013 and for the first, second and fourth quarters of 2013 because common share equivalents are excluded from the calculations of diluted weighted average shares outstanding for those quarters, as their effect is antidilutive.

- Definition

The entire disclosure for the quarterly financial data in the annual financial statements. The disclosure may include a tabular presentation of financial information for each fiscal quarter for the current and previous year, including revenues, gross profit, income or loss before extraordinary items and earnings per share data. It also includes an indication if the information in the note is unaudited, comments on the aggregate effect of year-end adjustments, and an explanation of matters or transactions that affect comparability or are pertinent to an understanding of the information furnished.

+ References + Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2013
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events The Company has evaluated subsequent events through the issuance date of these financial statements to ensure that this filing includes appropriate disclosure of events both recognized in the financial statements as of December 31, 2013, and events which occurred subsequently but were not recognized in the financial statements. In February 2014, the Company entered into an extension of a current facility lease for the period beginning March 2014 and ending June 2014. Future minimum payments under this extension total $0.1 million.

The Business and Summary of Significant Accounting Policies (Policy)

12 Months Ended

Dec. 31, 2013

The Business and Summary of Significant Accounting Policies [Abstract]

Description of Business

Cash and Cash Equivalents

The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market accounts.

Investments

Concentration of Credit Risk

Accounts Receivable

Fair Value of Financial Instruments

Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.

Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.

There was no material re-measurement to fair value of financial assets and liabilities that are not measured at fair value on a recurring basis.

Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:


			Fair Value Measurements at
			December 31, 2013
	December 31, 2013		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	107,349	$	107,349	$	—	$	—


			Fair Value Measurements at December 31, 2012
	December 31, 2012		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	17,687	$	16,381	$	1,306	$	—
Short-term investments		9,849		—		9,849		—
Redeemable convertible preferred stock warrant liability		7,512		—		—		7,512

Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):


	Fair Value Measurements (Level 3)
	(in thousands)
Redeemable Convertible Preferred Stock Warrant Liability
Balance at January 1, 2012	$	6,491
Issuance		174
Fair value increase recorded in other expense		847
Fair value at December 31, 2012		7,512
Fair value increase recorded in other expense		6,590
Reclassification of warrant liability to additional paid-in capital		(14,102	)
Fair value at December 31, 2013	$	—

Property and Equipment

Impairment of Long-Lived Assets

Deferred Public Offering Costs

Deferred Rent

Redeemable Convertible Preferred Stock Warrant Liability

Redeemable Convertible Preferred Stock

Revenue Recognition

Clinical Trial Accruals

Research and Development

Interest Expense, Net

Income Taxes

Share-Based Compensation

Basic and Dilutive Net Loss Per Share of Common Stock

Segments

The Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2013

The Business and Summary of Significant Accounting Policies [Abstract]

Assets and Liabilities Measured at Fair Value on a Recurring Basis

Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:


			Fair Value Measurements at
			December 31, 2013
	December 31, 2013		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	107,349	$	107,349	$	—	$	—


			Fair Value Measurements at December 31, 2012
	December 31, 2012		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents	$	17,687	$	16,381	$	1,306	$	—
Short-term investments		9,849		—		9,849		—
Redeemable convertible preferred stock warrant liability		7,512		—		—		7,512

Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis

Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):


	Fair Value Measurements (Level 3)
	(in thousands)
Redeemable Convertible Preferred Stock Warrant Liability
Balance at January 1, 2012	$	6,491
Issuance		174
Fair value increase recorded in other expense		847
Fair value at December 31, 2012		7,512
Fair value increase recorded in other expense		6,590
Reclassification of warrant liability to additional paid-in capital		(14,102	)
Fair value at December 31, 2013	$	—

Schedule of Prepaid and Other Current Assets

Prepaid and other current assets consist of the following:


	December 31, 2013		December 31, 2012
	(in thousands)
Prepaid development expenses	$	2,433	$	486
Deferred public offering costs		—		273
Other prepaid and other current assets		332		224
	$	2,765	$	983

Schedule of Accrued Liabilities

Accrued liabilities consist of the following:


	December 31, 2013		December 31, 2012
	(in thousands)
Accrued compensation	$	1,779	$	560
Accrued development expenses		350		98
Other accrued liabilities		291		248
	$	2,420	$	906

- Definition

Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and gains or losses recognized in other comprehensive income (loss) and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs) by class of liability.

+ References + Details

Investments (Tables)

12 Months Ended

Dec. 31, 2013

Investments [Abstract]

Summary of Available-for-Sale Securities

The following table summarizes available-for-sale securities as of December 31, 2012:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Corporate bonds	$	8,353	$	—	$	(2	)	$	8,351
Commercial paper		1,498		—		—			1,498
Total	$	9,851	$	—	$	(2	)	$	9,849

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27198-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 19, 20, 21
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 17
-Subparagraph a, b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 03-1
-Paragraph 21
-Subparagraph a, b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2013

Property and Equipment [Abstract]

Property and Equipment

Property and equipment consist of the following:


	December 31, 2013			December 31, 2012
	(in thousands)
Lab equipment	$	873		$	958
Leasehold improvements		78			78
Computer equipment		324			393
Office furniture and equipment		222			212
		1,497			1,641
Less accumulated depreciation		(1,159	)		(1,234	)
	$	338		$	407

Loan Payable (Tables)

12 Months Ended

Dec. 31, 2013

Loan Payable [Abstract]

Schedule of Future Payments under LSA

The future payments under the LSA are as follows (in thousands):



Years ending December 31,
2014	$	6,322
2015		4,508
		10,830
Less: amount representing interest		(780	)
Total payments under LSA	$	10,050

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2013

Commitments and Contingencies [Abstract]

Schedule of Future Minimum Rental Payments for Operating Leases

The Company has the following minimum payments under noncancelable operating lease obligations that existed at December 31, 2013 (in thousands):



Years ending December 31,
2014	$	331
2015		275
2016		245
2017		243
2018		41
	$	1,135

Redeemable Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2013

Summary of Authorized, Issued and Outstanding Shares of Redeemable Convertible Preferred Stock

The following table summarizes the authorized, issued and outstanding shares of redeemable convertible preferred stock as of December 31, 2012:


	Authorized Shares		Issued and Outstanding Shares
Series A		800,000		800,000
Series B		2,233,879		2,233,879
Series B-1		2,054,333		2,033,333
Series C		5,141,690		5,141,690
Series D		11,354,526		11,295,846
Series E		7,894,871		7,894,871
Series F		40,200,000		22,004,895
Total Shares		69,679,299		51,404,514

Common Stock [Member]

Schedule of Warrants Issued, Outstanding and Exercisable

The following warrants for the purchase of common stock were issued, outstanding and exercisable at December 31, 2013:

Class

Date

Price Per Share

Expiration

Common

February 7, 2011

1,337,845

7.26

February 2018

Redeemable Convertible Preferred Stock [Member]

Schedule of Warrants Issued, Outstanding and Exercisable

The following warrants for the purchase of preferred stock were issued, outstanding and exercisable at December 31, 2012:


Class	Date	Shares		Price Per Share		Expiration
Series B-1	November 5, 2003		21,000	$	1.500	November 2013
Series D	November 24, 2008		58,680	$	2.045	November 2018
Series F	February 7, 2011		5,501,215	$	2.045	February 2018
Series F	January 27, 2012		146,700	$	2.045	January 2022

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

- Definition

Tabular disclosure of temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References + Details

Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2013

Schedule of Shares Reserved for Future Issuance

The following shares of common stock reserved for future issuances:


	December 31, 2013		December 31, 2012

Conversion of preferred stock and preferred stock warrants		—		16,093,483
Exercise of common stock warrants		1,337,845		—
Stock options issued and outstanding		1,946,823		2,593,423
Restricted Stock units outstanding		-		43,199
Authorized for future purchases under the 2013 Employee Stock Purchase Plan		704,225		—
Authorized for future grants under the 2013 Equity Incentive Plan		1,681,932		—
Authorized for future grants under the 2012 Equity Incentive Plan		—		427,933
		5,670,825		19,158,038

Summary of Activity Related to Stock Options

A summary of activity related to the Company’s stock options is as follows:


	Number of Options Outstanding			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (in Years)
Balance, January 1, 2012		2,631,415		$	2.24		7.69
Granted		382,167			3.24		—
Exercised		(16,530	)		0.82		—
Expired or Canceled		(102,228	)		2.63		—
Forfeited		(301,401	)		1.69		—
Balance, December 31, 2012		2,593,423		$	2.45		7.36
Granted		292,906			10.62		—
Exercised		(801,049	)		2.43		—
Expired or Canceled		(2,816	)		1.57		—
Forfeited		(135,641	)		4.55		—
Balance, December 31, 2013		1,946,823		$	3.54		7.03
Exercisable at December 31, 2013		1,266,070		$	2.32		6.21
Vested or expected to vest at December 31, 2013		1,952,222		$	3.50		7.02

Fair Value of Option Vested and Share-Based Compensation Expense

The fair value of options vested and share-based compensation expense recognized are as follows:

	Year Ended December 31,
	2013		2012		2011
	(in thousands)
Research and development:
Employee	$	537	$	336	$	315
Non-employee		67		80		—
General and administrative:
Employee		458		921		651
Non-employee		82		59		—
	$	1,144	$	1,396	$	966

Summary of Activity Related to Restricted Stock Units

A summary of activity related to the Company’s RSUs is as follows:


	Number of Restricted Stock Units Outstanding
Balance, December 31, 2012		43,199
Granted		59,348
Share issuance		(102,547	)
Balance, December 31, 2013		—

Employee [Member]

Schedule of Fair Value Assumptions


	Employees
	Year Ended December 31,
	2013			2012			2011
Dividend yield		0.00	%		0.00	%		0.00	%
Weighted-average risk-free interest rate		1.49	%		0.86	%		2.85	%
Volatility		76.40	%		80.55	%		82.00	%
Expected term (in years)		6.1			6.0			7.0
Weighted-average fair value per option	$	2.52		$	1.93		$	1.74

Non-Employee [Member]

Schedule of Fair Value Assumptions


			Non-Employees
			Year Ended December 31,
	2013					2012			2011
Dividend yield				0.00	%		0.00	%		0.00	%
Weighted-average risk-free interest rate				1.30	%		0.78	%		0.40	%
Volatility				79.69	%		81.77	%		77.80	%
Expected term (in years)				6.2			5.8			2.7
Weighted-average fair value per option		$		5.01		$	3.48		$	3.38

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

Income Taxes [Abstract]

Components of Deferred Tax Assets and Liabilities

The components of deferred tax assets and liabilities at December 31, 2013 and 2012 are as follows:



	December 31,
	2013			2012
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	40,721		$	31,431
Research and development expenses		127			34
Capitalized Section 174 expenses		69			80
Research and development credits		2,640			941
Accrued bonuses		405			54
Other		497			445
Total gross deferred tax assets		44,459			32,985
Valuation allowance		(44,405	)		(32,841	)
		54			144
Deferred tax liabilities:
Other		(54	)		(144	)
Total deferred tax liabilities		(54	)		(144	)
Net deferred tax assets	$	—		$	—

Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate



	2013						2012						2011
	Amount			% of Pretax Earnings			Amount			% of Pretax Earnings			Amount			% of Pretax Earnings
	(in thousands)
Income tax benefit at statutory rate	$	(12,392	)		34.0	%	$	(1,499	)		34.0	%	$	(8,700	)		34.0	%
State income taxes		(852	)		2.3	%		(100	)		2.3	%		(1,164	)		4.6	%
Research and development credits		(2,265	)		6.2	%		—			0.0	%		(1,171	)		4.6	%
Permanent items		3,060			(8.4	)%		868			(19.7	)%		964			(3.8	)%
Provision to return adjustments		320			(0.9	)%		2			0.0	%		12			0.0	%
Effect of change in state tax rate		(1)			0.0	%		609			(13.9	)%		630			(2.5	)%
Increase in unrecognized tax benefits		566			(1.5	)%		—			0.0	%		314			(1.2	)%
Valuation allowance		11,564			(31.7	)%		120			(2.7	)%		9,115			(35.7	)%
Net benefit	$	—			0.0	%	$	—			0.0	%	$	—			0.0	%

Summary of Uncertain Tax Benefit

Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the year ended December 31, 2013, as follows (in thousands):



Balance at December 31, 2011	$	314
Increases related to 2012		—
Balance at December 31, 2012		314
Increase related to 2013		297
Increase related to prior periods		269
Balance at December 31, 2013	$	880

- Definition

Tabular disclosure of tax positions taken in the tax returns filed or to be filed for which it is more likely than not that the tax position will not be sustained upon examination by taxing authorities (i.e., uncertain tax positions) and other types of income tax contingencies, including: (1) the policy on classification of interest and penalties; (2) a tabular reconciliation of the total amounts of unrecognized tax benefits at the beginning and end of the period; the total amount(s) of: (3) unrecognized tax benefits that, if recognized, would affect the effective tax rate, and (4) interest and penalties recognized in each of the income statement and balance sheet; (5) for positions for which it is reasonably possible that the total amounts unrecognized will significantly change within 12 months of the reporting date the: (i) nature of the uncertainty, (ii) nature of the event that could occur that would cause the change, and (iii) an estimate of the range of the reasonably possible change or a statement that an estimate of the range cannot be made; and (6) a description of tax years that remain subject to examination by major tax jurisdictions.

+ References + Details

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2013

Selected Quarterly Financial Information [Abstract]

Schedule of Quarterly Financial Information


	2013 Quarter
	Fourth		Third		Second		First

Total revenues	$	879	$	912	$	808	$	1,771
Operating loss		(7,979)		(6,436)		(7,656)		(6,548)
Net loss		(8,174)		(6,706)		(12,459)		(9,107)
Net loss per common share, basic and diluted	$	(0.31)	$	(0.26)	$	(0.91)	$	(22.58)
Weighted average shares outstanding, basic and diluted		26,416,787		25,866,109		23,067,201		1,534,016


	2012 Quarter
	Fourth		Third		Second		First

Total revenues	$	3,581	$	20,856	$	6,205	$	3,078
Operating (loss) income		(4,143)		11,272		(4,422)		(5,490)
Net (loss) income		(4,326)		11,142		(4,324)		(6,898)
Net (loss) income per common share, basic	$	(3.90)	$	6.70	$	(3.44)	$	(5.14)
Net (loss) income per common share, diluted	$	(3.90)	$	0.11	$	(3.44)	$	(5.14)
Weighted average shares outstanding, basic		1,532,633		1,529,442		1,518,753		1,517,465
Weighted average shares outstanding, diluted		1,532,633		52,933,956		1,518,753		1,517,465

The Business and Summary of Significant Accounting Policies (Narrative) (Details)						12 Months Ended
	Oct. 23, 2013 shares	Apr. 16, 2013 USD ($) $ / shares shares	Apr. 10, 2013 $ / shares shares	Mar. 25, 2013 item	Apr. 10, 2010 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) segment $ / shares shares	Dec. 31, 2012 USD ($) $ / shares shares	Dec. 31, 2011 shares
Description of Business
Stock split, reverse description				the Company's board of directors approved and implemented a 3.55-for-1 reverse stock split of the Company's outstanding common stock
Reverse stock split, conversion ratio \| item				3.55
Issuance of common stock, per share price \| $ / shares						$ 14.00
Proceeds from initial public offering						$ 107,634,000
Offering expenses						10,217,696
Warrants to purchase common stock \| shares			41,323
Investments Related to Corporate Bonds and Commercial Paper
Available for sale securities losses, other-than-temporary						$ 0	$ 0
Fair Value of Financial Instruments
Volatility						79.69%	81.77%	77.80%
Expected term						6 years 2 months 12 days	5 years 9 months 18 days	2 years 8 months 12 days
Risk free interest rate						1.30%	0.78%	0.40%
Dividend yield						0.00%	0.00%	0.00%
Property and Equipment
Property and equipment, useful life, leasehold improvements						amortized over the shorter of the useful life of the asset or the term of the related lease
Impairment of long-lived assets						$ 0
Deferred Public Offering Costs
Deferred public offering costs							$ 273,000
Per share information:
Anti-dilutive securities excluded from the calculation loss per share \| shares						4,773,213	11,259,579	11,034,134
Segments
Number of operating segments \| segment						1
Over Allotment Options [Member]
Description of Business
Stock issued during the period, shares \| shares		1,098,000
Issuance of common stock, per share price \| $ / shares		$ 14.00
Issuance of common stock, value		$ 14,300,000
Public offering underwriting discounts and commissions		$ 1,100,000
IPO [Member]
Description of Business
Stock issued during the period, shares \| shares					7,320,000
Issuance of common stock, per share price \| $ / shares					$ 14.00
Proceeds from initial public offering					$ 93,300,000
Public offering underwriting discounts and commissions					7,100,000
Offering expenses					$ 2,100,000
Secondary Offering [Member]
Description of Business
Stock issued during the period, shares \| shares	2,476,995
Series F [Member]
Fair Value of Financial Instruments
Fair value \| $ / shares			$ 3.94
Series F [Member] \| IPO [Member]
Description of Business
Conversion of stock, shares converted \| shares			15,556,091
Warrant [Member]
Fair Value of Financial Instruments
Volatility			79.00%				79.00%
Expected term			2 years 6 months
Risk free interest rate			0.24%
Dividend yield			0.00%
Warrant [Member] \| IPO [Member]
Description of Business
Warrants to purchase common stock \| shares			1,613,395
Maximum [Member]
Property and Equipment
Property and equipment, useful life						5 years
Maximum [Member] \| Series F [Member]
Fair Value of Financial Instruments
Fair value \| $ / shares							$ 2.85
Maximum [Member] \| Warrant [Member]
Fair Value of Financial Instruments
Expected term							5 years
Expected liquidity							31.00%
Minimum [Member]
Property and Equipment
Property and equipment, useful life						3 years
Minimum [Member] \| Series F [Member]
Fair Value of Financial Instruments
Fair value \| $ / shares							$ 2.19
Minimum [Member] \| Warrant [Member]
Fair Value of Financial Instruments
Expected term							8 months
Expected liquidity							2.00%

The Business and Summary of Significant Accounting Policies (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Significant Unobservable Inputs (Level 3) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Liabilities, fair value		$ 7,512	$ 6,491
Cash Equivalents [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value	107,349	17,687
Cash Equivalents [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value	$ 107,349	16,381
Cash Equivalents [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value		1,306
Short-term Investments [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value		9,849
Short-term Investments [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value		9,849
Redeemable Convertible Preferred Stock [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Liabilities, fair value		7,512
Redeemable Convertible Preferred Stock [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Liabilities, fair value		$ 7,512

The Business and Summary of Significant Accounting Policies (Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis) (Details) - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Beginning of period	$ 7,512	$ 6,491
Issuance		174
Fair value increase recorded in other expense	6,590	847
Reclassification of warrant liability to additional paid-in capital	(14,102)
Ending period		$ 7,512

The Business and Summary of Significant Accounting Policies (Schedule of Prepaid and Other Current Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012
The Business and Summary of Significant Accounting Policies [Abstract]
Prepaid development expenses	$ 2,433	$ 486
Deferred public offering costs		273
Other prepaid and other current assets	332	224
Prepaid and other current assets, total	$ 2,765	$ 983

The Business and Summary of Significant Accounting Policies (Schedule of Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012
The Business and Summary of Significant Accounting Policies [Abstract]
Accrued compensation	$ 1,779	$ 560
Accrued development expenses	350	98
Other accrued liabilities	291	248
Accrued liabilities, current, total	$ 2,420	$ 906

- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References + Details

Investments (Details) - USD ($)	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Amortized cost		$ 9,851,000
Gross unrealized losses		(2,000)
Estimated fair value		$ 9,849,000
Investments maturity period, maximum		1 year
Short-term investments	$ 0
Long-term investments	$ 0
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized cost		$ 8,353,000
Gross unrealized losses		(2,000)
Estimated fair value		8,351,000
Commercial Paper [Member]
Schedule of Investments [Line Items]
Amortized cost		1,498,000
Estimated fair value		$ 1,498,000

- Definition

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 12
-Subparagraph b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13, 17
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 22
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 15C
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Section A
-Paragraph 4, 5
-Chapter 3
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 16
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 15D
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,497	$ 1,641
Less accumulated depreciation	(1,159)	(1,234)
Property and equipment, net	338	407
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	873	958
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	78	78
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	324	393
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 222	$ 212

- Definition

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

+ References + Details

Loan Payable (Narrative) (Details) $ in Thousands	12 Months Ended
Loan Payable (Narrative) (Details) $ in Thousands	Dec. 31, 2013 USD ($) $ / item shares	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Apr. 10, 2013 $ / item shares	Jan. 27, 2012 USD ($)	Feb. 07, 2011 $ / item
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity					$ 15,000
Interest expense	$ 1,232	$ 776	$ 212
Warrant strike price \| $ / item	2.045			7.26
Aggregate amount of advances, percentage	2.00%
Warrants to purchase common stock \| shares				41,323
Second Tranche [Member]
Line of Credit Facility [Line Items]
Loan and security agreement, remaining capacity					12,000
Interest only period	6 months
Principal and interest amortization period	32 months
First Tranche [Member]
Line of Credit Facility [Line Items]
Loan and security agreement, outstanding					$ 3,000
Loan payment	$ 2,600
Deferred financing costs	$ 100
Interest only period	12 months
Principal and interest amortization period	30 months
Loan and security agreement, interest rate	8.25%
Loan And Security Agreement [Member]
Line of Credit Facility [Line Items]
Interest expense	$ 100	$ 100
Series F [Member]
Line of Credit Facility [Line Items]
Warrant strike price \| $ / item						2.045
Series F [Member] \| Second Tranche [Member]
Line of Credit Facility [Line Items]
Warrants to purchase common stock \| shares	117,360
Series F [Member] \| First Tranche [Member]
Line of Credit Facility [Line Items]
Warrants to purchase common stock \| shares	29,340

Loan Payable (Schedule of Future Payments under LSA) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2013 USD ($)
Repayments of debt	$ 10,050
Principal and Interest Portion [Member]
Repayments of debt	10,830
Interest Portion [Member]
Repayments of debt	(780)
2014 [Member]
Repayments of debt	6,322
2015 [Member]
Repayments of debt	$ 4,508

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies [Abstract]
Operating leases, rent expense	$ 0.5	$ 0.4

Commitments and Contingencies (Schedule of Future Minimum Rental Payments for Operating Leases) (Details) $ in Thousands	Dec. 31, 2013 USD ($)
Commitments and Contingencies [Abstract]
2014	$ 331
2015	275
2016	245
2017	243
2018	41
Operating leases, future minimum payments due, total	$ 1,135

Redeemable Convertible Preferred Stock (Narrative) (Details) $ / shares in Units, $ in Thousands							12 Months Ended
	Nov. 05, 2013 shares	May 24, 2013 shares	Apr. 16, 2013 USD ($) shares	Apr. 10, 2013 $ / item shares	Jan. 27, 2012 $ / shares $ / item shares	Feb. 07, 2011 USD ($) $ / shares $ / item shares	Dec. 31, 2013 USD ($) $ / item shares	Dec. 31, 2012 USD ($) $ / shares
Redeemable convertible preferred stock issued							51,404,514
Redeemable convertible preferred stock, warrants issued						5,501,215
Aggregate number of common shares converted from redeemable convertible preferred stock				15,556,091
Proceeds from exercise of warrants \| $							$ 1,537
Warrants exercise price \| $ / item				7.26			2.045
Series F [Member]
Redeemable convertible preferred stock issued						22,004,895	22,004,895
Redeemable convertible preferred stock issued, par value per share \| $ / shares						$ 0.001
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares						$ 2.045		$ 2.045
Redeemable convertible preferred stock, warrants issued, issuance costs \| $						$ 200
Proceeds from issuance of redeemable preferred stock \| $						$ 45,000
Warrants expiration date								Feb. 01, 2018
Warrants exercise price \| $ / item						2.045
Series F [Member] \| Silicon Valley Bank [Member]
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares					$ 2.045
Redeemable convertible preferred stock, warrants issued					146,700
Percentage of the aggregate amount of advances made					2.00%
Series F [Member] \| IPO Completion [Member]
Redeemable convertible preferred stock, warrants issued				1,549,628
Warrants expiration date				Feb. 04, 2018
Warrants exercise price \| $ / item				7.26
Warrant [Member]
Other expense as a result of fair valuation of warrants \| $							$ 6,400	$ 800
Warrant [Member] \| Silicon Valley Bank [Member]
Redeemable convertible preferred stock, warrants issued					41,323
Warrants exercise price \| $ / item					7.26
Warrant [Member] \| IPO [Member]
Class of warrant or rights exercised			211,783
Proceeds from exercise of warrants \| $			$ 1,500
Warrant [Member] \| IPO Completion [Member]
Redeemable convertible preferred stock, warrants issued				1,613,395
Common Stock [Member]
Warrants expiration date							Feb. 01, 2018
Class of warrant or rights exercised	3,906	37,600
Warrants exercise price \| $ / item							7.26

Redeemable Convertible Preferred Stock (Summary of Authorized, Issued and Outstanding Shares of Redeemable Convertible Preferred Stock) (Details) - shares	Dec. 31, 2013	Feb. 07, 2011
Authorized shares	69,679,299
Issued and outstanding shares	51,404,514
Series A [Member]
Authorized shares	800,000
Issued and outstanding shares	800,000
Series B [Member]
Authorized shares	2,233,879
Issued and outstanding shares	2,233,879
Series B-1 [Member]
Authorized shares	2,054,333
Issued and outstanding shares	2,033,333
Series C [Member]
Authorized shares	5,141,690
Issued and outstanding shares	5,141,690
Series D [Member]
Authorized shares	11,354,526
Issued and outstanding shares	11,295,846
Series E [Member]
Authorized shares	7,894,871
Issued and outstanding shares	7,894,871
Series F [Member]
Authorized shares	40,200,000
Issued and outstanding shares	22,004,895	22,004,895

- Definition

The maximum number of securities classified as temporary equity that are permitted to be issued by an entity's charter and bylaws. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References + Details

Redeemable Convertible Preferred Stock (Schedule of Warrants Issued, Outstanding and Exercisable) (Details)	12 Months Ended
	Dec. 31, 2013 $ / item shares	Dec. 31, 2012 $ / shares shares	Apr. 10, 2013 $ / item	Feb. 07, 2011 $ / shares $ / item
Warrants exercise price \| $ / item	2.045		7.26
Series B-1 [Member]
Warrants date exercisable		Nov. 05, 2003
Warrants issued, outstanding and exercisable		21,000
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares		$ 1.500
Warrants expiration date		Nov. 01, 2013
Series D [Member]
Warrants date exercisable		Nov. 24, 2008
Warrants issued, outstanding and exercisable		58,680
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares		$ 2.045
Warrants expiration date		Nov. 01, 2018
Series F [Member]
Warrants date exercisable		Feb. 07, 2011
Warrants issued, outstanding and exercisable		5,501,215
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares		$ 2.045		$ 2.045
Warrants exercise price \| $ / item				2.045
Warrants expiration date		Feb. 01, 2018
Series F 2nd Occurrence [Member]
Warrants date exercisable		Jan. 27, 2012
Warrants issued, outstanding and exercisable		146,700
Redeemable convertible preferred stock issued, redemption price per share \| $ / shares		$ 2.045
Warrants expiration date		Jan. 01, 2022
Common Stock [Member]
Warrants date exercisable	Feb. 07, 2011
Warrants issued, outstanding and exercisable	1,337,845
Warrants exercise price \| $ / item	7.26
Warrants expiration date	Feb. 01, 2018

Stockholders' Equity (Deficit) (Narrative) (Details) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 2013	Feb. 28, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 10, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized			200,000,000	89,700,000
Common stock, shares issued			26,664,972	1,533,996
Common stock, shares outstanding			26,664,972	1,533,996
Number of shares outstanding under the plan			1,946,823	2,593,423	2,631,415
Aggregate intrinsic value of options outstanding			$ 16,200,000
Aggregate intrinsic value of options exercisable			16,200,000
Intrinsic value of options exercised			12,400,000	$ 18,000	$ 16,000
Exercise of stock options			1,946,000	14,000	$ 30,000
Tax benefit from stock options exercised			$ 0	$ 0
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense, allocated	$ 1,900,000
The 2012 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized to be granted				427,933		244,717
The 2013 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized to be granted			1,681,932			1,408,450
Percentage of total number of shares of capital stock outstanding			2.50%
Unrecognized compensation costs			$ 2,500,000
Unrecognized compensation costs, period of recognition			2 years 6 months 15 days
The 2013 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized to be granted		704,225	704,225
Number of shares authorized, increase amount		422,535
Percentage of total number of shares of capital stock outstanding		1.00%
Modified Grants [Member] \| Three Individuals [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in compensation expense				$ 30,000
Modified Grants [Member] \| One Individual [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in compensation expense				$ 300,000
Maximum [Member] \| The 2013 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized to be granted			2,816,901

Stockholders' Equity (Deficit) (Schedule of Shares Reserved for Future Issuance) (Details) - shares	Dec. 31, 2013	Apr. 10, 2013	Feb. 28, 2013	Dec. 31, 2012
Conversion of preferred stock and preferred stock warrants				16,093,483
Exercise of common stock warrants	1,337,845
Stock options issued and outstanding	1,946,823			2,593,423
Restricted Stock units outstanding				43,199
Shares of common stock reserved for future issuance	5,670,825			19,158,038
The 2012 Plan [Member]
Authorized for future grants under the plan		244,717		427,933
The 2013 Plan [Member]
Authorized for future grants under the plan	1,681,932	1,408,450
The 2013 ESPP [Member]
Authorized for future grants under the plan	704,225		704,225

Stockholders' Equity (Deficit) (Assumption Used to Determine the Fair Value of Options Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Expected term	6 years 2 months 12 days	5 years 9 months 18 days	2 years 8 months 12 days
Volatility	79.69%	81.77%	77.80%
Weighted-average risk-free interest rate	1.30%	0.78%	0.40%
Weighted-average fair value per option	$ 5.01	$ 3.48	$ 3.38
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Expected term	6 years 1 month 6 days	6 years	7 years
Volatility	76.40%	80.55%	82.00%
Weighted-average risk-free interest rate	1.49%	0.86%	2.85%
Weighted-average fair value per option	$ 2.52	$ 1.93	$ 1.74

Stockholders' Equity (Deficit) (Summary of Activity Related to Stock Options) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stockholders' Equity (Deficit) [Abstract]
Number of options outstanding, Beginning balance	2,593,423	2,631,415
Number of options outstanding, Granted	292,906	382,167
Number of options outstanding, Exercised	(801,049)	(16,530)
Number of options outstanding, Expired or Canceled	(2,816)	(102,228)
Number of options outstanding, Forfeited	(135,641)	(301,401)
Number of options outstanding, Ending balance	1,946,823	2,593,423	2,631,415
Number of options outstanding, Exercisable	1,266,070
Number of options outstanding, Vested and expected to vest	1,952,222
Weighted-average exercise price, beginning balance	$ 2.45	$ 2.24
Weighted-average exercise price, Granted	10.62	3.24
Weighted-average exercise price, Exercised	2.43	0.82
Weighted-average exercise price, Expired or Canceled	1.57	2.63
Weighted-average exercise price, Forfeited	4.55	1.69
Weighted-average exercise price, Ending balance	3.54	$ 2.45	$ 2.24
Weighted-average exercise price, Exercisable	2.32
Weighted-average exercise price, Vested or expected to vest	$ 3.50
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	7 years 11 days	7 years 4 months 10 days	7 years 8 months 9 days
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	7 years 11 days	7 years 4 months 10 days	7 years 8 months 9 days
Weighted-average remaining contractual life (in years), Exercisable	6 years 2 months 16 days
Weighted-average remaining contractual life (in years), Vested or expected to vest	7 years 7 days

Stockholders' Equity (Deficit) (Summary of Activity Related to Restricted Stock Units) (Details)	12 Months Ended
	Dec. 31, 2013 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Balance, December 31, 2012	43,199
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Balance, December 31, 2012	43,199
Granted	59,348
Shares issuance	(102,547)

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2007	Dec. 31, 2002	Jan. 01, 2014	Dec. 31, 2011
Loss limitation ownership change benchmark amount	$ 6,700,000		$ 762,000	$ 64,000
Excess tax benefits from exercise of stock options in net operating loss carryforwards	7,300,000
Increase to valuation allowance, deferred tax assets	1,200,000	$ 1,100,000
Unrecognized tax benefits, gross	880,000	314,000				$ 314,000
Domestic Tax Authority [Member]
Operating loss carryforwards	$ 117,500,000	83,600,000
Operating loss carryforwards, expiration dates	2020
Tax credit carryforward, deferred tax asset	$ 3,500,000
Tax credit carryforward, expiration date	Dec. 31, 2022
State and Local Jurisdiction [Member]
Operating loss carryforwards	$ 106,000,000	$ 65,800,000
Operating loss carryforwards, expiration dates	2023
Minimum [Member]
Income tax examination, year under examination	2000
Maximum [Member]
Income tax examination, year under examination	2013
Subsequent Event [Member]
Income tax examination, penalties and interest accrued					$ 0

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Net operating loss carryforwards	$ 40,721	$ 31,431
Research and development expenses	127	34
Capitalized Section 174 expenses	69	80
Research and development credits	2,640	941
Accrued bonuses	405	54
Other	497	445
Total gross deferred tax assets	44,459	32,985
Valuation allowance	(44,405)	(32,841)
Deferred tax assets, net of valuation allowance, total	54	144
Deferred Tax Liabilities, Gross [Abstract]
Other	(54)	(144)
Total deferred tax liabilities	(54)	(144)
Net deferred tax assets

Income Taxes (Components of the Net Income Tax Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]
Valuation allowance	$ (11,564)	$ (120)	$ (9,115)

Income Taxes (Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate) (Alternate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]
Income tax benefit at statutory rate	$ (12,392)	$ (1,499)	$ (8,700)
Income tax benefit at statutory rate, tax rate	34.00%	34.00%	34.00%
State income taxes	$ (852)	$ (100)	$ (1,164)
State income taxes, tax rate	2.30%	2.30%	4.60%
Research and development credits	$ (2,265)		$ (1,171)
Research and development credits, tax rate	6.20%	0.00%	4.60%
Permanent items	$ 3,060	$ 868	$ 964
Permanent items, tax rate	(8.40%)	(19.70%)	(3.80%)
Provision to return adjustments	$ 320	$ 2	$ 12
Provision to return adjustments, tax rate	(0.90%)	0.00%	0.00%
Effect of change in state tax rate	$ (1)	$ 609	$ 630
Effect of change in state tax rate, tax rate	0.00%	(13.90%)	(2.50%)
Increase in unrecognized tax benefits	$ 566		$ 314
Increase in unrecognized tax benefits, tax rate	(1.50%)	0.00%	(1.20%)
Valuation allowance	$ 11,564	$ 120	$ 9,115
Valuation allowance, tax rate	(31.70%)	(2.70%)	(35.70%)
Net income tax benefit, tax rate	0.00%	0.00%	0.00%

Income Taxes (Summary of Uncertain Tax Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Abstract]
Beginning balance	$ 314	$ 314
Increase related to 2013	297
Increase related to prior periods	269
Ending balance	$ 880	$ 314

Significant Agreements (Details) $ in Thousands	1 Months Ended			12 Months Ended
Significant Agreements (Details) $ in Thousands	Dec. 31, 2013 USD ($)	Jul. 31, 2012 USD ($)	May 31, 2002 USD ($) shares	Dec. 31, 2013 USD ($) contract shares	Dec. 31, 2012 USD ($) shares	Dec. 31, 2011 USD ($)
Long-term Purchase Commitment [Line Items]
Number of options outstanding, Granted \| shares				292,906	382,167
Contract revenue				$ 4,370	$ 16,275	$ 12,046
CMX001 [Member]
Long-term Purchase Commitment [Line Items]
Sublicense fee payable, maximum percentage				5.00%
CMX157 [Member]
Long-term Purchase Commitment [Line Items]
Sublicense fee payable, maximum percentage				10.00%
Merck, Sharp and Dohme Corp. [Member]
Long-term Purchase Commitment [Line Items]
Upfront payment, receivable		$ 17,500
Product royalty period		10 years
Regents Of University Of California [Member]
Long-term Purchase Commitment [Line Items]
Number of options outstanding, Granted \| shares			64,788
Sublicense fee percentage			50.00%
Royalties percentage				50.00%
Other expenses				$ 0	$ 900
Length of first option segment period				12 months
Research and Development Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue	$ 5,300
Other segments, period				1 year
Maximum [Member] \| CMX157 [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments			$ 3,400
Maximum [Member] \| Merck, Sharp and Dohme Corp. [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments		$ 151,000
Maximum [Member] \| Research and Development Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Number of extension periods \| contract				4
Maximum [Member] \| Research and Development Arrangement [Member] \| Scenario, Plan [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue				$ 5,300
Reimbursement revenue				$ 75,800

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statements Of Operations And Comprehensive Loss [Abstract]
Total revenues	$ 879	$ 912	$ 808	$ 1,771	$ 3,581	$ 20,856	$ 6,205	$ 3,078	$ 4,370	$ 33,720	$ 12,101
Operating (loss) income	(7,979)	(6,436)	(7,656)	(6,548)	(4,143)	11,272	(4,422)	(5,490)	(28,619)	(2,783)	(24,992)
Net (loss) income	$ (8,174)	$ (6,706)	$ (12,459)	$ (9,107)	$ (4,326)	$ 11,142	$ (4,324)	$ (6,898)	$ (36,445)	$ (4,406)	$ (25,589)
Net loss per common share, basic and diluted	$ (0.31)	$ (0.26)	$ (0.91)	$ (22.58)					$ (3.65)	$ (5.75)	$ (23.49)
Weighted-average shares outstanding, basic and diluted	26,416,787	25,866,109	23,067,201	1,534,016					19,307,422	1,524,628	1,496,262
Net (loss) income per common share, basic					$ (3.90)	$ 6.70	$ (3.44)	$ (5.14)
Net (loss) income per common share, diluted					$ (3.90)	$ 0.11	$ (3.44)	$ (5.14)
Weighted-average shares outstanding, basic					1,532,633	1,529,442	1,518,753	1,517,465
Weighted-average shares outstanding, diluted					1,532,633	52,933,956	1,518,753	1,517,465

Subsequent Events (Details) $ in Thousands	Dec. 31, 2013 USD ($)
Operating leases, future minimum payments due, total	$ 1,135
Subsequent Event [Member] \| Current Extension on Facility [Member]
Operating leases, future minimum payments due, total	$ 100