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Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Mar. 31, 2014	May 01, 2014
Document Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2014
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q1
Entity Registrant Name	CHIMERIX INC
Entity Central Index Key	0001117480
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		26,965,570

Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 37,421	$ 109,976
Short-term investments, available-for-sale	62,500
Accounts receivable	89	248
Prepaid and other current assets	1,691	2,765
Deferred financing costs, current portion	20	20
Total current assets	101,721	113,009
Property and equipment, net of accumulated depreciation	387	338
Deposits	32	30
Deferred financing costs, less current portion	13	10
Total assets	102,153	113,387
Current liabilities:
Accounts payable	1,806	2,214
Accrued liabilities	1,894	2,420
Loan payable, current portion	5,590	5,573
Total current liabilities	9,290	10,207
Other long-term liabilities	350	347
Loan payable, less current portion	2,889	4,294
Total liabilities	12,529	14,848
Common Stock:
Preferred stock, $0.001 par value, 10,000,000 shares authorized at March 31, 2014 and December 31, 2013; no shares issued and outstanding as of March 31, 2014 and December 31, 2013
Common stock, $0.001 par value, 200,000,000 shares authorized at March 31, 2014 and December 31, 2013; 26,932,607 and 26,664,972 shares issued and outstanding as of March 31, 2014 and December 31, 2013, respectively	27	26
Additional paid-in capital	262,739	261,243
Accumulated other comprehensive loss	(32)
Accumulated deficit	(173,110)	(162,730)
Total stockholders' deficit	89,624	98,539
Total liabilities and stockholders' equity	$ 102,153	$ 113,387

Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2014	Dec. 31, 2013
Balance Sheets [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	26,932,607	26,664,972
Common stock, shares outstanding	26,932,607	26,664,972

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues:
Contract revenue	$ 780	$ 1,771
Total revenues	780	1,771
Operating expenses:
Research and development	8,292	6,783
General and administrative	2,672	1,536
Loss from operations	(10,184)	(6,548)
Interest expense, net	(196)	(356)
Other expense:
Fair value adjustments to warrant liability		(2,203)
Net loss	(10,380)	(9,107)
Other comprehensive loss:
Unrealized loss on securities available-for-sale	(32)	(1)
Comprehensive loss	(10,412)	(9,108)
Net loss	(10,380)	(9,107)
Accretion of redeemable convertible preferred stock		(25,525)
Net loss attributable to common stockholders	$ (10,380)	$ (34,632)
Per share information:
Net loss per common share, basic and diluted	$ (0.39)	$ (22.58)
Weighted-average shares outstanding, basic and diluted	26,762,264	1,534,016

Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Mar. 31, 2014	Mar. 31, 2013
Operating activities
Net loss	$ (10,380)	$ (9,107)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	50	68
Non-cash interest expense	42	65
Amortization/accretion of premium/discount on investments	108	74
Share-based compensation costs	772	265
Deferred lease obligation	3
Fair value measurement of redeemable convertible preferred stock warrant liability		2,203
Changes in operating assets and liabilities:
Accounts receivable	159	(445)
Prepaid expenses and other current assets and deposits	1,064	(722)
Accounts payable and accrued liabilities	(934)	1,554
Net cash used by operating activities	(9,116)	(6,045)
Investing activities:
Purchase of property and equipment	(99)	(52)
Purchase of short-term investments	(62,640)	(1,853)
Maturities of short-term investments		750
Net cash used by investing activities	(62,739)	(1,155)
Financing activities:
Proceeds from exercise of stock options	496	8
Proceeds from employee stock purchase plan issuance	229
Repayment of loan payable	(1,425)	(675)
Net cash used by financing activities	(700)	(667)
Decrease in cash and cash equivalents	(72,555)	(7,867)
Cash and cash equivalents, beginning of period	109,976	19,906
Cash and cash equivalents, end of period	37,421	12,039
Supplemental cash flow information:
Interest payments	$ 198	$ 44

The Business and Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2014

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, Inc. (the Company) 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 regimens. 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 Sharp & Dohme Corporation (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 of common stock 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 generally accepted accounting principles (GAAP) in the United States of America. 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.

The accompanying interim financial statements are unaudited. The unaudited interim financial statements have been prepared in accordance with GAAP on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair statement of the Company’s financial position, results of operations and cash flows for the dates and periods presented herein. These financial statements should be read in conjunction with the financial statements for the year ended December 31, 2013 and notes thereto set forth in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013. Interim operating results are not necessarily indicative of operating results for the full year.

Reclassifications

In certain instances, amounts previously reported in the Company’s 2013 financial statements have been reclassified to conform to the Company’s 2014 financial statement presentation. Such reclassifications had no effect on net loss or stockholders’ equity as previously reported.

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, commercial paper and certificates of deposit. 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 equity. 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 short-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 three months ended March 31, 2014 and the year ended December 31, 2013.

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 March 31, 2014 and December 31, 2013 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.

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.

The following table presents information about certain assets and liabilities measured at fair value on a recurring basis:

			Fair Value Measurements at March 31, 2014
	March 31, 2014		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	$	36,509	$	28,560	$	7,949	$	—
Short-term investments		62,500		—		62,500		—

			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	$	—	$	—

Short-term investments consist of corporate bonds, commercial paper and certificates of deposit.

Prepaid and Other Current Assets

Prepaid and other current assets consist of the following:

	March 31, 2014		December 31, 2013
	(in thousands)
Prepaid development expenses	$	1,086	$	2,433
Interest receivable		341		—
Other prepaid and other current assets		264		332
	$	1,691	$	2,765

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 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:


	March 31, 2014		December 31, 2013
	(in thousands)
Accrued compensation	$	1,106	$	1,779
Accrued development expenses		594		350
Other accrued liabilities		194		291
	$	1,894	$	2,420

Revenue Recognition

The Company’s revenues generally consist of contract revenue – revenue generated under federal contracts. 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.

Clinical Trial Accruals/Prepaids

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. Depending on amounts paid to the contract research organization and other third-party vendors as compared to actual expenses incurred, there might be a prepaid balance recorded as a prepaid asset. The Company determines accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of completion 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 March 31, 2014, 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 March 31, 2014, 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 Diluted Net Loss Per Common Share

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 common share 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 for the three months ended March 31, 2014 and 2013.

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 3,100,454 and 11,511,182 for the three months ended March 31, 2014 and 2013, 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 2013, the Financial Accounting Standards Board issued ASU 2013-11, “Income Taxes, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryfoward, a Similar Tax Loss, or a Tax Credit Carryfoward Exists (a consensus of the FASB Emerging Issues Taskforce)” (ASU 2013-11). Beginning January 1, 2014 the date this regulation became effective on us, the Company adopted the provisions of ASU 2013-11 related to presentation of an unrecognized tax benefit when a net operating loss carryfoward, a similar tax benefit, or a tax credit carryfoward exists. Adoption of ASU 2013-11 did not have a material impact on the Company’s financial statements.

Investments

3 Months Ended

Mar. 31, 2014

Investments [Abstract]

Investments

2. Investments

The following table summarizes available-for-sale securities:

	March 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(in thousands)
Corporate bonds	$	35,258	$	1	$	(27)	$	35,232
Commercial paper		22,474		1		—		22,475
Certificates of deposit		4,800		—		(7)		4,793
Total	$	62,532	$	2	$	(34)	$	62,500

The Company had no short or long-term investments at December 31, 2013. All of the Company’s investments as of March 31, 2014 had maturities of one year or less.

- Definition

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

+ References + Details

Property and Equipment

3 Months Ended

Mar. 31, 2014

Property and Equipment [Abstract]

Property and Equipment

3. Property and Equipment

Property and equipment consist of the following:

	March 31, 2014			December 31, 2013
	(in thousands)
Lab equipment	$	904		$	873
Leasehold improvements		117			78
Computer equipment		352			324
Office furniture and equipment		223			222
		1,596			1,497
Less accumulated depreciation		(1,209	)		(1,159	)
	$	387		$	338

Loan Payable	3 Months Ended
Loan Payable	Mar. 31, 2014
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 $27,000 and $38,000 was included in interest expense for the three months ended March 31, 2014 and 2013, respectively. Concurrently with entering into the LSA, the Company also granted SVB a warrant to purchase shares of Series F 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. In May 2013, SVB exercised the warrant in full and it is no longer outstanding.

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2014
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. Rent expense under non-cancelable operating leases and other month-to-month equipment rental agreements, including common area maintenance fees, totaled approximately $0.1 million and $0.1 million for the three months ended March 31, 2014 and 2013, 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 March 31, 2014 and December 31, 2013.

Stockholders' Equity

3 Months Ended

Mar. 31, 2014

Stockholders' Equity [Abstract]

Stockholders' Deficit

6. Stockholders’ Equity

Common Stock

The Company’s common stock consists of 200.0 million shares authorized at March 31, 2014 and December 31, 2013, respectively, and 26.9 million and 26.7 million shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively.

Shares Reserved for Future Issuance

The following shares of common stock reserved for future issuances:



	March 31, 2014		December 31, 2013
Preferred stock		—		—
Exercise of common stock warrants		1,337,845		1,337,845
Stock options issued and outstanding		2,446,246		1,946,823
Authorized for future purchases under the Company’s 2013 Employee Stock Purchase Plan		956,690		704,225
Authorized for future grants under the Company’s 2013 Equity Incentive Plan		1,595,682		1,681,932
		6,336,463		5,670,825

Warrants

Upon the completion of the Company’s IPO, all outstanding warrants to purchase redeemable convertible preferred stock were marked to market resulting in a $2.2 million fair value adjustment for the three months ended March 31, 2013. The warrants were then converted into warrants to purchase 1,613,395 shares of common stock and were 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 March 31, 2014:

Class

Date

Price Per Share

Expiration

Common

February 7, 2011

1,337,845

7.26

February 2018

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 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. On January 1, 2014, the common stock reserved for issuance under the 2013 Plan was automatically increased by 666,624 shares.

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.

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 authorizes 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. On January 1, 2014, the common stock reserved for issuance under the ESPP was automatically increased by 266,649 shares.

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, December 31, 2013		1,946,823		$	3.54		7.03
Granted		754,620			18.39		—
Exercised		(253,451	)		1.96		—
Forfeited		(1,746	)		2.35		—
Balance, March 31, 2014		2,446,246		$	8.29		7.90
Exercisable at March 31, 2014		1,135,239		$	2.93		6.41
Vested or expected to vest at March 31, 2014		2,406,254		$	8.21		7.88

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:

	Three Months Ended March 31,
	2014		2013
	(in thousands)
Research and development:
Employee	$	303	$	107
Non-employee		—		16
General and administrative:
Employee		366		142
Non-employee		—		—
	$	669	$	265

Employee Stock Purchase Plans

The Company has reserved a total of 970,874 shares of common stock to be purchased under the ESPP, of which 956,690 shares remain available for purchase at March 31, 2014. Eligible employees may authorize up to 15% of their salary to purchase common stock at the lower of 85% of the beginning price or 85% of the ending price during each six-month purchase interval. The Company issued 14,184 shares of common stock pursuant to the ESPP during the three months ended March 31, 2014. Compensation expense for shares purchased under the ESPP related to the purchase discount and the “look-back” option were determined using a Black-Scholes option pricing model. For the three months ended March 31, 2014, $0.1 million was recorded. There was no compensation expense recorded for the three months ended March 31, 2013 since the ESPP was not active during that period.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2014
Income Taxes [Abstract]
Income Taxes	7. Income Taxes The Company estimates an annual effective tax rate of 0% for the year ending December 31, 2014 as the Company incurred losses for the three month period ended March 31, 2014 and is forecasting additional losses through the 4th quarter, resulting in an estimated net loss for both financial statement and tax purposes for the year ending December 31, 2014. Therefore, no federal or state income taxes are expected and none have been recorded at this time. Income taxes have been accounted for using the liability method in accordance with FASB ASC 740. Due to the Company's history of losses since inception, there is not enough evidence at this time to support that the Company will generate future income of a sufficient amount and nature to utilize the benefits of its net deferred tax assets. Accordingly, the deferred tax assets have been reduced by a valuation allowance, since it has been determined that it is more likely than not that all of the deferred tax assets will not be realized. At March 31, 2014, the Company had no unrecognized tax benefits that would reduce the Company’s effective tax rate if recognized.

Significant Agreements	3 Months Ended
Significant Agreements	Mar. 31, 2014
Significant Agreements [Abstract]
Significant Agreements	8. 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 (including UC Patent Rights relating to brincidofovir or CMX157) 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. The Company did not recognize expenses under this agreement for the three months ended March 31, 2014 or 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 development of brincidofovir as a medical countermeasure in the event of a smallpox release. The contract has been amended several times, most recently on April 10, 2014, to extend the first option segment until August 31, 2014. Under the contract, BARDA will reimburse the Company, plus pay a fixed fee, for the research and development of brincidofovir as a 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. In April 2014, the Company and BARDA extended the term of the first option segment to a period of 15 months, currently scheduled to end on August 31, 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 Chimerix. Therefore, the milestone method will not be applied to those payments.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2014
Subsequent Event [Abstract]
Subsequent Events	9. Subsequent Event Kenneth I. Moch, the Company’s Chief Executive Officer, resigned on April 9, 2014. The Company entered into a severance agreement with the former CEO that provides for severance benefits to him in connection with his resignation. Under the severance agreement, he will receive the benefits to which he would have been entitled under the amended severance plan upon a termination without cause. These benefits are (i) continued payment of his base salary for fifteen months following his separation date (the “Severance Period”), (ii) payment of COBRA benefits for the Severance Period and (iii) accelerated vesting of all of his outstanding stock options as if he had continued service over the Severance Period. In addition, Mr. Moch will have until December 31, 2014 to exercise his vested stock options. The continued payment of Mr. Moch’s base salary for fifteen months will amount to approximately $0.6 million, which will be expensed through general and administrative expense on the date of his resignation. The acceleration of vesting of Mr. Moch’s outstanding stock options as if he had completed service for the severance period and the extension of the period in which to exercise his options each represents a modification of his option award. The expense related to these modifications will be recorded to general and administrative expense on the resignation date. The amount of expense related to the modifications is in the process of being analyzed by the Company.

The Business and Summary of Significant Accounting Policies (Policy)

3 Months Ended

Mar. 31, 2014

The Business and Summary of Significant Accounting Policies [Abstract]

Description of Business

Reclassification

Reclassifications

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.

The following table presents information about certain assets and liabilities measured at fair value on a recurring basis:

			Fair Value Measurements at March 31, 2014
	March 31, 2014		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	$	36,509	$	28,560	$	7,949	$	—
Short-term investments		62,500		—		62,500		—

			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	$	—	$	—

Short-term investments consist of corporate bonds, commercial paper and certificates of deposit.

Property and Equipment

Impairment of Long-Lived Assets

Deferred Rent

Revenue Recognition

Clinical Trial Accruals/Prepaids

Research and Development

Interest Expense, Net

Income Taxes

Share-Based Compensation

Basic and Diluted Net Loss Per Common Share

Segments

The Business and Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2014

The Business and Summary of Significant Accounting Policies [Abstract]

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table presents information about certain assets and liabilities measured at fair value on a recurring basis:

			Fair Value Measurements at March 31, 2014
	March 31, 2014		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	$	36,509	$	28,560	$	7,949	$	—
Short-term investments		62,500		—		62,500		—

			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	$	—	$	—

Schedule of Prepaid and Other Current Assets

Prepaid and other current assets consist of the following:

	March 31, 2014		December 31, 2013
	(in thousands)
Prepaid development expenses	$	1,086	$	2,433
Interest receivable		341		—
Other prepaid and other current assets		264		332
	$	1,691	$	2,765

Schedule of Accrued Liabilities

Accrued liabilities consist of the following:


	March 31, 2014		December 31, 2013
	(in thousands)
Accrued compensation	$	1,106	$	1,779
Accrued development expenses		594		350
Other accrued liabilities		194		291
	$	1,894	$	2,420

Investments (Tables)

3 Months Ended

Mar. 31, 2014

Investments [Abstract]

Summary of Available-for-Sale Securities

The following table summarizes available-for-sale securities:

	March 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(in thousands)
Corporate bonds	$	35,258	$	1	$	(27)	$	35,232
Commercial paper		22,474		1		—		22,475
Certificates of deposit		4,800		—		(7)		4,793
Total	$	62,532	$	2	$	(34)	$	62,500

- 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 + Details

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2014

Property and Equipment [Abstract]

Property and Equipment

Property and equipment consist of the following:

	March 31, 2014			December 31, 2013
	(in thousands)
Lab equipment	$	904		$	873
Leasehold improvements		117			78
Computer equipment		352			324
Office furniture and equipment		223			222
		1,596			1,497
Less accumulated depreciation		(1,209	)		(1,159	)
	$	387		$	338

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2014

Schedule of Shares Reserved for Future Issuance

The following shares of common stock reserved for future issuances:



	March 31, 2014		December 31, 2013
Preferred stock		—		—
Exercise of common stock warrants		1,337,845		1,337,845
Stock options issued and outstanding		2,446,246		1,946,823
Authorized for future purchases under the Company’s 2013 Employee Stock Purchase Plan		956,690		704,225
Authorized for future grants under the Company’s 2013 Equity Incentive Plan		1,595,682		1,681,932
		6,336,463		5,670,825

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, December 31, 2013		1,946,823		$	3.54		7.03
Granted		754,620			18.39		—
Exercised		(253,451	)		1.96		—
Forfeited		(1,746	)		2.35		—
Balance, March 31, 2014		2,446,246		$	8.29		7.90
Exercisable at March 31, 2014		1,135,239		$	2.93		6.41
Vested or expected to vest at March 31, 2014		2,406,254		$	8.21		7.88

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:

	Three Months Ended March 31,
	2014		2013
	(in thousands)
Research and development:
Employee	$	303	$	107
Non-employee		—		16
General and administrative:
Employee		366		142
Non-employee		—		—
	$	669	$	265

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 March 31, 2014:

Class

Date

Price Per Share

Expiration

Common

February 7, 2011

1,337,845

7.26

February 2018

- 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

The Business and Summary of Significant Accounting Policies (Narrative) (Details) $ / shares in Units, $ in Millions				3 Months Ended
	Oct. 23, 2013 shares	Apr. 10, 2013 USD ($) $ / shares shares	Mar. 25, 2013	Mar. 31, 2014 segment shares	Mar. 31, 2013 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			3.55
Stock issued during the period, shares		7,320,000
Stock price, initial public offering \| $ / shares		$ 14.00
Proceeds from initial public offering \| $		$ 93.3
Public offering underwriting discounts and commissions \| $		7.1
Secondary public offering underwritten by company	2,476,995
Offering expenses \| $		$ 2.1
Number of operating segments \| segment				1
Per share information:
Anti-dilutive securities excluded from the calculation loss per share				3,100,454	11,511,182
Over Allotment Options [Member]
Description Of Business
Stock issued during the period, shares		1,098,000
Stock issued during the period, value \| $		$ 14.3
Stock price, initial public offering \| $ / shares		$ 14.00
Public offering underwriting discounts and commissions \| $		$ 1.1
Series F [Member]
Description Of Business
Conversion of stock, shares converted		15,556,091
Warrant [Member]
Description Of Business
Conversion of stock, shares converted		1,613,395
Maximum [Member]
Property And Equipment
Property and equipment, useful life				5 years
Minimum [Member]
Property And Equipment
Property and equipment, useful life				3 years

The Business and Summary of Significant Accounting Policies (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value	$ 36,509	$ 107,349
Cash and 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	28,560	$ 107,349
Cash and 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	7,949
Cash and Cash Equivalents [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value
Short-term Investments [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value	62,500
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	62,500
Short-term Investments [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Assets, fair value

The Business and Summary of Significant Accounting Policies (Schedule of Prepaid and Other Current Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
The Business and Summary of Significant Accounting Policies [Abstract]
Prepaid development expenses	$ 1,086	$ 2,433
Interest receivable	341
Other prepaid and other current assets	264	332
Prepaid and other current assets, total	$ 1,691	$ 2,765

The Business and Summary of Significant Accounting Policies (Schedule of Accrued Liabilties) (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
The Business and Summary of Significant Accounting Policies [Abstract]
Accrued compensation	$ 1,106	$ 1,779
Accrued development expenses	594	350
Other accrued liabilities	194	291
Accrued liabilities, current, total	$ 1,894	$ 2,420

Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Amortized cost	$ 62,532
Gross unrealized gains	2
Gross unrealized losses	(34)
Estimated fair value	$ 62,500
Investments maturity period, maximum	1 year	1 year
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized cost	$ 35,258
Gross unrealized gains	1
Gross unrealized losses	(27)
Estimated fair value	35,232
Commercial Paper [Member]
Schedule of Investments [Line Items]
Amortized cost	22,474
Gross unrealized gains	1
Estimated fair value	22,475
Certificates of Deposit [Member]
Schedule of Investments [Line Items]
Amortized cost	4,800
Gross unrealized losses	(7)
Estimated fair value	$ 4,793

Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,596	$ 1,497
Less accumulated depreciation	(1,209)	(1,159)
Property and equipment, net	387	338
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	904	873
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	117	78
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	352	324
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 223	$ 222

Loan Payable (Details) - USD ($)	3 Months Ended
Loan Payable (Details) - USD ($)	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Nov. 05, 2013	May 24, 2013	Apr. 16, 2013	Jan. 27, 2012
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity							$ 15,000,000
Interest expense	$ 196,000	$ 356,000
Warrants to purchase common stock		41,323		3,906	37,600	211,783
Second Tranche [Member]
Line of Credit Facility [Line Items]
Loan and security agreement, remaining capacity							12,000,000
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							$ 3,000,000
Loan payment			$ 2,600,000
Deferred financing costs			$ 100,000
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	$ 27,000	$ 38,000

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Commitments and Contingencies [Abstract]
Operating leases, rent expense	$ 0.1	$ 0.1

Stockholders' Equity (Narrative) (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 02, 2014	Apr. 16, 2013	Apr. 10, 2013	Feb. 28, 2013	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Nov. 05, 2013	May 24, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized					200,000,000		200,000,000
Common stock, shares issued					26,932,607		26,664,972
Common stock, shares outstanding					26,932,607		26,664,972
Redeemable convertible preferred stock, warrants issued						1,613,395
Number of shares authorized to be granted					1,595,682		1,681,932
Fair value adjustment of warrants						$ 2.2
Warrants to purchase common stock		211,783				41,323		3,906	37,600
Proceeds from exercise of warrants		$ 1.5
Number of shares outstanding under the plan					2,446,246		1,946,823
Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual rerm					7 years 10 months 24 days		7 years 11 days
Shares remaining available for purchase					956,690		704,225
2013 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of total number of shares of capital stock outstanding				1.00%
ESOP shares available to plan				704,225	970,874
Shares remaining available for purchase					956,690
Increase in shares under the plan	266,649			422,535
Percentage of pay that employee can contribute, maximum					15.00%
Percentage of fair value employees pay					85.00%
Shares issued					14,184
Compensation expense					$ 0.1
The 2013 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized to be granted			1,408,450
Additional shares authorized	666,624		244,717
Percentage of total number of shares of capital stock outstanding					2.50%
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 (Schedule of Shares Reserved for Future Issuance) (Details) - shares	Mar. 31, 2014	Dec. 31, 2013
Stockholders' Equity [Abstract]
Preferred stock
Exercise of commons stock warrants	1,337,845	1,337,845
Stock options issued and outstanding	2,446,246	1,946,823
Authorized for future purchases under the Company's 2013 Employee Stock Purchase Plan	956,690	704,225
Authorized for future grants under the Company's 2013 Equity Incentive Plan	1,595,682	1,681,932
Shares of common stock reserved for future issuance	6,336,463	5,670,825

Stockholders' Equity (Schedule of Warrants Issued, Outstanding and Exercisable) (Details) - Common Stock [Member]	3 Months Ended
	Mar. 31, 2014 $ / item shares
Warrants date exercisable	Feb. 07, 2011
Warrants issued, outstanding and exercisable \| shares	1,337,845
Warrants exercise price \| $ / item	7.26
Warrants expiration date	Feb. 01, 2018

Stockholders' Equity (Summary of Activity Related to Stock Options) (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Stockholders' Equity [Abstract]
Number of options outstanding, Beginning balance	1,946,823
Number of options outstanding, Granted	754,620
Number of options outstanding, Exercised	(253,451)
Number of options outstanding, Forfeited	(1,746)
Number of options outstanding, Ending balance	2,446,246	1,946,823
Number of options outstanding, Exercisable	1,135,239
Number of options outstanding, Vested and expected to vest	2,406,254
Weighted-average exercise price, beginning balance	$ 3.54
Weighted-average exercise price, Granted	18.39
Weighted-average exercise price, Exercised	1.96
Weighted-average exercise price, Forfeited	2.35
Weighted-average exercise price, Ending balance	8.29	$ 3.54
Weighted-average exercise price, Exercisable	2.93
Weighted-average exercise price, Vested or expected to vest	$ 8.21
Weighted-average remaining contractual life (in years)	7 years 10 months 24 days	7 years 11 days
Weighted-average remaining contractual life (in years), Exercisable	6 years 4 months 28 days
Weighted-average remaining contractual life (in years), Vested or expected to vest	7 years 10 months 17 days

Stockholders' Equity (Fair Value of Option Vested and Share-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value of option vested and allocated share-based compensation expense	$ 669	$ 265
Research and Development Expense [Member] \| Employee [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value of option vested and allocated share-based compensation expense	303	107
Research and Development Expense [Member] \| Non-Employee [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value of option vested and allocated share-based compensation expense		16
General and Administrative Expense [Member] \| Employee [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value of option vested and allocated share-based compensation expense	366	142
General and Administrative Expense [Member] \| Non-Employee [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value of option vested and allocated share-based compensation expense

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($)	Dec. 31, 2014	Mar. 31, 2014
Income Taxes [Abstract]
Estimated annual effective tax rate	0.00%
Unrecognized tax benefits		$ 0

Significant Agreements (Details) $ in Thousands	1 Months Ended			3 Months Ended
Significant Agreements (Details) $ in Thousands	Jul. 31, 2012 USD ($)	Feb. 28, 2011 USD ($) item	May 31, 2002 USD ($) shares	Mar. 31, 2014 USD ($) shares	Mar. 31, 2013 USD ($)
Long-term Purchase Commitment [Line Items]
Number of options outstanding, Granted \| shares				754,620
Contract revenue				$ 780	$ 1,771
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]
Milestone payments			$ 3,400
Number of options outstanding, Granted \| shares			64,788
Research and Development Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue		$ 5,300
Other segments, period		1 year
Maximum [Member] \| Merck, Sharp and Dohme Corp. [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments	$ 151,000
Maximum [Member] \| Regents of University of California [Member]
Long-term Purchase Commitment [Line Items]
Sublicense fee percentage			50.00%
Royalties percentage			50.00%
Maximum [Member] \| Regents of University of California [Member] \| Brincidofovir [Member]
Long-term Purchase Commitment [Line Items]
Sublicense fee amount, payable fee percentage				5.00%
Maximum [Member] \| Regents of University of California [Member] \| CMX157 [Member]
Long-term Purchase Commitment [Line Items]
Sublicense fee amount, payable fee percentage				10.00%
Maximum [Member] \| Research and Development Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Reimbursement revenue		$ 75,800
Number of extension periods \| item		4
Maximum [Member] \| Research and Development Arrangement [Member] \| Scenario, Plan [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue					$ 5,300

Subsequent Event (Narrative) (Details) - Subsequent Event [Member] - Chief Executive Officer [Member] $ in Millions	1 Months Ended
	Apr. 30, 2014 USD ($)
Subsequent Event [Line Items]
Period of continued employment	P15M
Continued payment expense	$ 0.6