View Filing Data

Document And Entity Information - shares	6 Months Ended
Document And Entity Information - shares	Jun. 30, 2015	Jul. 30, 2015
Document Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Entity Registrant Name	CHIMERIX INC
Entity Central Index Key	0001117480
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		46,068,592

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 127,776	$ 128,462
Short-term investments, available-for-sale	130,555	106,114
Accounts receivable	2,311	106
Prepaid expenses and other current assets	8,651	2,775
Total current assets	269,293	237,457
Long-term investments	150,139	52,973
Property and equipment, net of accumulated depreciation	1,996	1,310
Other long-term assets	80	138
Total assets	421,508	291,878
Current liabilities:
Accounts payable	9,819	5,938
Accrued liabilities	10,758	6,833
Loan payable, net	1,484	4,296
Total current liabilities	22,061	17,067
Long-term liabilities	134	175
Total liabilities	22,195	17,242
Commitments and contingencies	0	0
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized at June 30, 2015 and December 31, 2014; no shares issued and outstanding as of June 30, 2015 and December 31, 2014	0	0
Common stock, $0.001 par value, 200,000,000 shares authorized at June 30, 2015 and December 31, 2014; 45,847,032 and 41,031,770 shares issued and outstanding as of June 30, 2015 and December 31, 2014, respectively	46	41
Additional paid-in capital	666,586	496,602
Accumulated other comprehensive gain, net	1,803	35
Accumulated deficit	(269,122)	(222,042)
Total stockholders’ equity	399,313	274,636
Total liabilities and stockholders’ equity	$ 421,508	$ 291,878

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [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	45,847,032	41,031,770
Common Stock, Shares, Outstanding	45,847,032	41,031,770

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues:
Contract revenue	$ 2,598	$ 919	$ 3,833	$ 1,699
Collaboration and licensing revenue	1,545	0	1,548	0
Total revenues	4,143	919	5,381	1,699
Operating expenses:
Research and development	21,762	8,092	39,205	16,384
General and administrative	7,332	4,423	13,455	7,095
Total operating expenses	29,094	12,515	52,660	23,479
Loss from operations	(24,951)	(11,596)	(47,279)	(21,780)
Other income (expense):
Interest income (expense), net	136	(138)	199	(334)
Net loss	(24,815)	(11,734)	(47,080)	(22,114)
Other comprehensive loss:
Unrealized gain (loss) on investments, net	1,144	12	1,769	(20)
Comprehensive loss	$ (23,671)	$ (11,722)	$ (45,311)	$ (22,134)
Per share information:
Net loss, basic and diluted	$ (0.59)	$ (0.39)	$ (1.13)	$ (0.78)
Weighted-average shares outstanding, basic and diluted	42,079,716	30,111,380	41,614,494	28,446,074

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net loss	$ (47,080)	$ (22,114)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	264	95
Amortization of debt costs	49	83
Amortization of premium/discount on investments	783	385
Share-based compensation	5,203	1,415
Amortization of deferred lease obligation	(15)	0
Changes in operating assets and liabilities:
Accounts receivable	(2,205)	(40)
Prepaid expenses and other assets	(5,828)	(489)
Accounts payable and accrued liabilities	6,972	1,912
Net cash used in operating activities	(41,857)	(18,753)
Cash flows from investing activities:
Purchase of property and equipment	(950)	(226)
Purchase of short-term investments	(33,669)	(88,641)
Purchase of long-term investments	(147,086)	0
Sales of short-term investments	1,003	0
Maturities of short-term investments	60,005	7,240
Net cash used in investing activities	(120,697)	(81,627)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,445	781
Proceeds from employee stock purchase plan stock purchases	461	229
Proceeds from exercise of warrants	1,000	0
Proceeds from public offering, net of offering costs	161,880	111,845
Repayment of debt	2,850	2,850
Payments for deferred financing costs	(68)	0
Net cash provided by financing activities	161,868	110,005
Net (decrease) increase in cash and cash equivalents	(686)	9,625
Cash and cash equivalents, beginning of period	128,462	109,976
Cash and cash equivalents, end of period	127,776	119,601
Supplemental disclosure cash flow information:
Cash paid for interest	$ 132	$ 370

The Business and Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

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 conjugate technology to unlock the potential of some of the most potent broad-spectrum antivirals by enhancing their antiviral activity and safety profiles in convenient, orally administered dosing regimens. Based on the Company’s proprietary lipid conjugate technology, its lead compound, brincidofovir (BCV or CMX001), is in Phase 3 clinical development; in addition, the Company has an active discovery program focusing on viral targets for which limited or no therapies are currently available or where current therapies have significant liabilities.

Basis of Presentation

The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiary and have been prepared in accordance with U.S. generally accepted accounting principles (GAAP), for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Company’s audited financial statements and notes thereto included in its Annual Report on Form 10-K for the year ended December 31, 2014. In the opinion of the Company’s management, all adjustments, consisting of normal recurring adjustments, necessary for a fair presentation of its financial position, operating results and cash flows for the periods presented have been included. Operating results for the three and six months ended June 30, 2015 are not necessarily indicative of the results that may be expected for the full year, for any other interim period or for any future year.

Fair Value of Financial Instruments

The carrying amounts of certain financial instruments, including accounts 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.

At June 30, 2015 and December 31, 2014, the Company had cash equivalents, consisting of money market accounts, and short-term and long-term investments consisting of U.S. Treasury securities, whose value is based on using quoted market prices. Accordingly, these securities are classified as Level 1.

At June 30, 2015 and December 31, 2014, the Company had cash equivalents, short-term investments and long-term investments comprised of corporate bonds, commercial paper and brokered certificates of deposit for which quoted prices are not available that are 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 Company’s preferred stock investment in ContraVir Pharmaceuticals (NASDAQ: CTRV) (ContraVir) is categorized as Level 3 as there are significant unobservable inputs. The valuation of the investment at June 30, 2015 and December 31, 2014 was calculated on an as if converted to common share basis with a discount for lack of marketability applied due to the 18 month restriction from the date of the investment on selling the converted common shares. An option pricing model was used to determine the discount for lack of marketability of 23% and 25% at June 30, 2015 and December 31, 2014, respectively. The key unobservable inputs used in the option pricing model at June 30, 2015 were (i) exercise price - $5.08, (ii) dividend yield - 0%, (iii) expected holding period - 0.97 years, (iv) risk-free rate - 0.28%, and (v) volatility - 65%. The key unobservable inputs used in the option pricing model at December 31, 2014 were (i) exercise price - $2.22, (ii) dividend yield - 0%, (iii) expected holding period - 1.5 years, (iv) risk-free rate - 0.44%, and (v) volatility - 65%. The increase in valuation of the preferred stock for the three and six months ended June 30, 2015 was recorded as an unrealized gain in investment, net of tax in the Consolidated Statements of Operations and Comprehensive Loss.

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 (in thousands):



	Fair Value Measurements
	June 30, 2015
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	117,537	$	117,537	$	—	$	—
Certificates of deposit	240		—		240		—
Commercial paper	9,999		—		9,999		—
Total cash equivalents	127,776		117,537		10,239		—
Short-term investments
Certificates of deposit	25,646		—		25,646		—
Corporate bonds	23,409		—		23,409		—
Commercial paper	3,999		—		3,999		—
U.S. Treasury securities	73,310		73,310		—		—
Preferred stock of U.S. corporation	4,191		—		—		4,191
Total short-term investments	130,555		73,310		53,054		4,191
Long-term investments
Certificates of deposit	18,261		—		18,261		—
U.S. Treasury securities	131,878		131,878		—		—
Total long-term investments	150,139		131,878		18,261		—
Total assets	$	408,470	$	322,725	$	81,554	$	4,191

	Fair Value Measurements
	December 31, 2014
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	125,606	$	125,606	$	—	$	—
Certificates of deposit	480		—		480		—
Total cash equivalents	126,086		125,606		480		—
Short-term investments
Certificates of deposit	16,981		—		16,981		—
Corporate bonds	69,892		—		69,892		—
Commercial paper	11,240		—		11,240		—
U.S. Treasury securities	8,000		8,000		—		—
Total short-term investments	106,114		8,000		98,114		—
Long-term investments
Certificates of deposit	10,996		—		10,996		—
U.S. Treasury securities	40,197		40,197		—		—
Preferred stock of U.S. corporation	1,781		—		—		1,781
Total long-term investments	52,973		40,197		10,996		1,781
Total assets	$	285,173	$	173,803	$	109,590	$	1,781

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



	Fair Value Measurements (Level 3)
Preferred stock of U.S. corporation:
Fair value at December 31, 2014	$	1,781
Fair value increase recorded in other comprehensive gain	2,410
Fair value at June 30, 2015	$	4,191

Revenue Recognition

The Company’s revenues generally consist of (i) contract and grant revenue – revenue generated under federal contracts and other awarded grants, and (ii) collaboration and licensing revenue – revenue 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.

Research and Development Prepaids and 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. 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 June 30, 2015, 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.

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 warrants and options to purchase common stock and employee stock purchase plan rights. 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 warrants and options to purchase common stock 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 net loss per share of common stock for the three and six months ended June 30, 2015 and 2014.

The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of warrants and options to purchase common stock and employee stock purchase plan rights, as the impact of such items are anti-dilutive during periods of net loss. Potential common shares excluded from the calculations were 1.2 million and 2.4 million for the three months ended June 30, 2015 and 2014, respectively, and 1.3 million and 2.5 million for the six months ended June 30, 2015 and 2014, respectively.

Impact of Recently Issued Accounting Standards

In June 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-12, “Compensation — Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period.” The amendments in this update require that a performance target that affects vesting and that could be achieved after the requisite service period should be treated as a performance condition. A reporting entity should apply existing guidance in Topic 718 as it relates to awards with performance conditions that affect vesting to account for such awards. As such, the performance target should not be reflected in estimating the grant-date fair value of the award. ASU 2014-12 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. Earlier adoption is permitted. The Company does not expect the adoption of ASU 2014-12 to have a material impact on its consolidated financial statements.

In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers (Topic 606)." The ASU establishes a principles-based approach for accounting for revenue arising from contracts with customers and supersedes existing revenue recognition guidance. The ASU provides that an entity should apply a five-step approach for recognizing revenue, including (1) identify the contract with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when, or as, the entity satisfies a performance obligation. Also, the entity must provide various disclosures concerning the nature, amount and timing of revenue and cash flows arising from contracts with customers. ASU 2014-09 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2016. Earlier adoption is not permitted. The Company is currently analyzing the impact of this new accounting guidance.

In April 2015, the FASB issued ASU No. 2015-03, “Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs,” which requires debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of the associated debt liability, and amortization of those costs should be reported as interest expense. This ASU is effective for financial statements issued for annual and interim periods beginning after December 15, 2015, and early adoption is permitted for financial statements that have not been previously issued. The new guidance should be applied on a retrospective basis for each period presented in the balance sheet. The Company does not expect the adoption of ASU 2015-03 to have a material impact on its consolidated financial statements.

In June 2015, the FASB issued ASU 2015-10, “Technical Corrections and Improvements.” The amendments in ASU 2015-10 will clarify and correct some of the difference that arose between original guidance from FASB, EITF and other sources, and the translation into the new Codification. ASU 2015-10 is effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. The Company does not expect the adoption of ASU 2015-10 to have a material impact on its consolidated financial statements.

Equity Transactions and Share-based Compensation

6 Months Ended

Jun. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-based Compensation

Equity Transactions and Share-based Compensation

Common Stock

On June 16, 2015, the Company completed an underwritten public offering of 4,341,250 shares of common stock, including 566,250 shares sold pursuant to the full exercise of an option granted to the underwriters to purchase additional shares of common stock. All of the shares were offered by the Company at a price to the public of $39.75 per share. The net proceeds from this offering, after deducting underwriting discounts and commissions and other offering expenses payable by the Company, were approximately $161.9 million.

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. The number of shares of common stock reserved for future issuance automatically increases on January 1 of each calendar year by 4% 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. On January 1, 2015, the common stock reserved for issuance under the 2013 Plan was automatically increased by 1,641,271 shares. As of June 30, 2015, there was a total of 1,785,375 shares reserved for future issuance under the 2013 Plan.

Employee Stock Purchase Plan

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. Initially, the ESPP 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 automatically increases on January 1 of each calendar year, from January 1, 2014 through January 1, 2023 by the lesser 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). On January 1, 2015, the common stock reserved for issuance under the ESPP was automatically increased by an additional 410,317 shares bringing the total number of shares of common stock that may be purchased under the ESPP to 1,329,277.

The Company has reserved a total of 1,381,191 shares of common stock to be purchased under the ESPP, of which 1,329,277 shares remained available for purchase as of June 30, 2015. 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 ESPP also provides for an automatic reset feature to start participants on a new twenty-four month participation period in the event that the common stock market value on a purchase date is less than the common stock value on the first day of the twenty-four month offering period. The Company did not issue any shares of common stock pursuant to the ESPP for the three months ended June 30, 2015 and 2014. The Company issued 25,639 and 14,184 shares of common stock pursuant to the ESPP for the six months ended June 30, 2015 and 2014, respectively. 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 awards with only service conditions and graded-vesting features, the Company recognizes compensation expense on a straight-line basis over the requisite service period. For the three and six months ended June 30, 2015 and 2014, there was no non-employee share-based compensation expense. Employee-related compensation expense recognized related to stock options, RSUs and the ESPP is as follows (in thousands):



	Three Months Ended June 30,					Six Months Ended June 30,
	2015		2014			2015		2014
Research and development expense	$	1,202	$	(471	)	$	2,226	$	(96	)
General and administrative expense	1,599		1,115			2,977		1,511
Total share-based compensation expense	$	2,801	$	644		$	5,203	$	1,415

Significant Agreements	6 Months Ended
Significant Agreements	Jun. 30, 2015
Significant Agreements [Abstract]
Significant Agreements	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. 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 connection with the development and commercialization of brincidofovir, 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. In addition, upon commercialization of any product utilizing the UC Patent Rights (which would include the commercialization of brincidofovir), 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) the Company is obligated to pay to UC a fee, which amount will vary depending upon the amount of any payments 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, the fee payable to UC will not exceed 5% of the sublicense fee. 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 and six months ended June 30, 2015 and 2014. 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. On August 28, 2014, the second option segment of the contract to provide approximately $17.0 million through November 30, 2015 was executed. On July 14, 2015, the contract was amended to extend the period of performance for the second option segment through June 30, 2016. Under the contract, BARDA will reimburse the Company, plus pay a fixed fee, for the research and development of brincidofovir as a treatment for smallpox infections. The contract consists of an initial performance period, referred to as the base performance segment, plus up to four extension periods, referred to as option segments, each of which may be exercised at BARDA’s sole discretion. Under the contract as currently in effect, the Company may cumulatively receive up to $75.8 million in expense reimbursement and $5.3 million in fees if all remaining option segments are exercised. As of June 30, 2015, we had recognized revenue in aggregate of $40.6 million with respect to the base performance segment and the first two extension periods. For the three months ended June 30, 2015 and 2014, the Company recognized revenue under this contract of $2.6 million and $0.9 million, respectively, and for the six months ended June 30, 2015 and 2014, the Company recognized revenue under this contract of, $3.8 million and $1.7 million, respectively. ContraVir Pharmaceuticals On December 17, 2014, the Company entered into a license agreement with ContraVir Pharmaceuticals (NASDAQ: CTRV) for the development and commercialization of CMX157, our clinical stage nucleotide analog, for certain antiviral indications. Under the terms of the agreement, ContraVir has sole responsibility with respect to the control of the development and commercialization of CMX157. In exchange for the license to CMX157 rights, the Company received an upfront payment consisting of 120,000 shares of ContraVir Series B Convertible Preferred Stock with a stated value of $1.2 million. In addition, the Company is eligible to receive up to approximately $20.0 million in clinical, regulatory and initial commercial milestones in the United States and Europe, as well as royalties and additional milestones based on commercial sales in those territories. Either party may terminate the license agreement upon the occurrence of a material breach by the other party (subject to standard cure periods), or upon certain events involving the bankruptcy or insolvency of the other party. ContraVir may also terminate the license agreement without cause on a country-by-country basis upon 60 days’ prior written notice. The upfront payment of 120,000 shares of ContraVir Series B Convertible Preferred Stock was valued at $1.5 million at the time of the agreement. During the fourth quarter of 2014, the Company recorded this amount as a long-term investment and deferred revenue, which was included in accrued liabilities in the Consolidated Balance Sheets. Upon the completion of the transfer of the investigational new drug (IND) and technical know-how related to CMX157, the Company recognized the upfront payment as revenue during the three months ended June 30, 2015. As of June 30, 2015 and December 31, 2014, the fair value of the investment was $4.2 million and $1.8 million, respectively.

The Business and Summary of Significant Accounting Policies (Policy)

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Description of Business

Basis of Presentation

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 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.

Revenue Recognition

Clinical Trial Accruals/Prepaids

Research and Development Prepaids and Accruals

Basic and Diluted Net Loss Per Common Share

- Definition

Disclosure of accounting policy for revenue recognition. If the entity has different policies for different types of revenue transactions, the policy for each material type of transaction is generally disclosed. If a sales transaction has multiple element arrangements (for example, delivery of multiple products, services or the rights to use assets) the disclosure may indicate the accounting policy for each unit of accounting as well as how units of accounting are determined and valued. The disclosure may encompass important judgment as to appropriateness of principles related to recognition of revenue. The disclosure also may indicate the entity's treatment of any unearned or deferred revenue that arises from the transaction.

+ References + Details

The Business and Summary of Significant Accounting Policies (Narrative) (Details) - $ / shares	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounting Policies [Abstract]
Fair value, investments, redemption restriction period			18 months
Fair value inputs, discount for lack of marketability			23.00%		25.00%
Fair value assumptions, exercise price	$ 5.08		$ 5.08		$ 2.22
Fair value assumptions, expected divided rate			0.00%		0.00%
Fair value assumptions, expected term			354 days		1 year 6 months
Fair value assumptions, risk free interest rate			0.28%		0.44%
Fair value assumptions, expected volatility rate			65.00%		65.00%
Anti-dilutive securities excluded from the calculation loss per share	1,211,728	2,448,026	1,311,946	2,547,571

The Business and Summary of Significant Accounting Policies (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	$ 130,555	$ 106,114
Long-term investments	150,139	52,973
Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	127,776	126,086
Short-term investments, available-for-sale	130,555	106,114
Long-term investments	150,139	52,973
Assets, fair value	408,470	285,173
Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	117,537	125,606
Short-term investments, available-for-sale	73,310	8,000
Long-term investments	131,878	40,197
Assets, fair value	322,725	173,803
Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	10,239	480
Short-term investments, available-for-sale	53,054	98,114
Long-term investments	18,261	10,996
Assets, fair value	81,554	109,590
Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Short-term investments, available-for-sale	4,191	0
Long-term investments	0	1,781
Assets, fair value	4,191	1,781
Money market funds \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	117,537	125,606
Money market funds \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	117,537	125,606
Money market funds \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Money market funds \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Certificates of deposit \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	240	480
Short-term investments, available-for-sale	25,646	16,981
Long-term investments	18,261	10,996
Certificates of deposit \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Short-term investments, available-for-sale	0	0
Long-term investments	0	0
Certificates of deposit \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	240	480
Short-term investments, available-for-sale	25,646	16,981
Long-term investments	18,261	10,996
Certificates of deposit \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Short-term investments, available-for-sale	0	0
Long-term investments	0	0
Corporate bonds \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	23,409	69,892
Corporate bonds \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0	0
Corporate bonds \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	23,409	69,892
Corporate bonds \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0	0
Commercial paper \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	9,999
Short-term investments, available-for-sale	3,999	11,240
Commercial paper \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0
Short-term investments, available-for-sale	0	0
Commercial paper \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	9,999
Short-term investments, available-for-sale	3,999	11,240
Commercial paper \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0
Short-term investments, available-for-sale	0	0
U.S. Treasury securities \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	73,310	8,000
Long-term investments	131,878	40,197
U.S. Treasury securities \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	73,310	8,000
Long-term investments	131,878	40,197
U.S. Treasury securities \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0	0
Long-term investments	0	0
U.S. Treasury securities \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0	0
Long-term investments	0	0
Preferred stock of U.S. corporation
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	4,191
Long-term investments		1,781
Fair value increase recorded in other comprehensive gain	2,410
Preferred stock of U.S. corporation \| Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	4,191
Long-term investments		1,781
Preferred stock of U.S. corporation \| Fair value, measurements, recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0
Long-term investments		0
Preferred stock of U.S. corporation \| Fair value, measurements, recurring \| Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	0
Long-term investments		0
Preferred stock of U.S. corporation \| Fair value, measurements, recurring \| Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale	$ 4,191
Long-term investments		$ 1,781

Stock-based Compensation (Narrative) (Details) - shares	3 Months Ended		6 Months Ended
Stock-based Compensation (Narrative) (Details) - shares	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Feb. 28, 2013
The 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation, Evergreen Option Provision, Equity Increase			4.00%
Additional shares authorized			1,641,271
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,785,375		1,785,375
The 2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation, Evergreen Option Provision, Equity Increase			1.00%
Additional shares authorized			410,317
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,329,277		1,329,277
Number of shares authorized to be granted	1,381,191		1,381,191		704,225
Number of shares outstanding under the plan			422,535
Percentage of pay that employee can contribute, maximum	15.00%		15.00%
Discounted Purchase Price	85.00%		85.00%
Shares issued	0	0	25,639	14,184

Significant Agreements (Details) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended		22 Months Ended	53 Months Ended	65 Months Ended
Significant Agreements (Details) $ in Thousands	Dec. 17, 2014 USD ($) shares	May 31, 2002 USD ($) shares	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) extension	Jun. 30, 2014 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2014 USD ($)
Long-term Purchase Commitment [Line Items]
Operating Expenses			$ 29,094	$ 12,515	$ 52,660	$ 23,479
Contract revenue			2,598	919	3,833	1,699
Estimated Fair Value			280,694		280,694			$ 280,694		$ 159,087
Preferred stock of U.S. corporation
Long-term Purchase Commitment [Line Items]
Estimated Fair Value			4,191		4,191			4,191		1,781
Regents of University of California
Long-term Purchase Commitment [Line Items]
Number of options outstanding, Granted \| shares		64,788
Operating Expenses			0	0	0	0
Regents of University of California \| Maximum [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments		$ 3,400
Sublicense fee percentage		50.00%
Royalties percentage		50.00%
Regents of University of California \| Maximum [Member] \| Brincidofovir
Long-term Purchase Commitment [Line Items]
Sublicense fee amount, payable fee percentage		5.00%
BARDA [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue			2,600	$ 900	$ 3,800	$ 1,700		40,600
Number of extension periods \| extension					4
BARDA [Member] \| Maximum [Member] \| Scenario, Forecast [Member]
Long-term Purchase Commitment [Line Items]
Reimbursement revenue									$ 75,800
Fees and Commissions, Other									$ 5,300
BARDA [Member] \| Maximum [Member] \| Second Option Segment [Member] \| Scenario, Forecast [Member]
Long-term Purchase Commitment [Line Items]
Contract revenue							$ 17,000
ContraVir Pharmaceuticals
Long-term Purchase Commitment [Line Items]
Other Significant Noncash Transaction, Shares Received as Consideration \| shares	120,000
Other Significant Noncash Transaction, Value of Consideration Received	$ 1,200
ContraVir Pharmaceuticals \| Preferred stock of U.S. corporation
Long-term Purchase Commitment [Line Items]
Estimated Fair Value	$ 1,500		$ 4,200		$ 4,200			$ 4,200		$ 1,800
ContraVir Pharmaceuticals \| Maximum [Member]
Long-term Purchase Commitment [Line Items]
Collaboration and licensing revenue					$ 20,000

Loan Payable	6 Months Ended
Loan Payable	Jun. 30, 2015
Debt Disclosure [Abstract]
Loan Payable	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. The borrowings under the LSA are collateralized by a security interest in all of the Company’s assets, excluding its intellectual property. The first tranche, which was paid in full as of June 30, 2015, had an interest-only period of twelve months followed by a principal and interest amortization period of 30 months with interest being charged at 8.25% per year. The second tranche, which had an outstanding principal balance of $1.5 million as of June 30, 2015, has an interest-only period of 6 months followed by a principal and interest amortization period of 32 months with interest being charged at 8.25%. There are certain fees in accordance with the LSA which are being recorded as discounts or short-term liabilities depending on the nature of the fees and are being accreted through interest expense over the life of the loans.

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 2021. Rent expense under non-cancelable operating leases and other month-to-month equipment rental agreements, including common area maintenance fees, totaled approximately $0.2 million and $0.2 million for the three months ended June 30, 2015 and 2014, respectively, and $0.3 million and $0.3 million for the six months ended June 30, 2015 and 2014, respectively. Significance of Revenue Source The Company is the recipient of federal research contract funds from the Biomedical Advanced Research and Development Authority (BARDA), the primary source of the Company's contract revenue. Periodic audits are required under the Company’s BARDA agreement and certain costs may be questioned as appropriate under the BARDA agreement. Management believes that such amounts in the current year, if any, are not significant. Accordingly, no provision for refundable amounts under the BARDA agreement has been made as of June 30, 2015 and December 31, 2014.

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company estimates an annual effective tax rate of 0% for the year ending December 31, 2015 as the Company incurred losses for the six month period ended June 30, 2015 and is forecasting additional losses through the fourth quarter, resulting in an estimated net loss for both financial statement and tax purposes for the year ending December 31, 2015. 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 Accounting Standards Codification 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 full valuation allowance, since the Company does not currently believe that realization of its deferred tax assets is more likely than not. As of June 30, 2015, the Company had no unrecognized tax benefits that would reduce the Company’s effective tax rate if recognized.

Subsequent Event	6 Months Ended
Subsequent Event	Jun. 30, 2015
Subsequent Events [Abstract]
Subsequent Events	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 June 30, 2015, and events which occurred subsequently but were not recognized in the financial statements.

Investments - Summary of Available-for-Sale securities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Amortized Cost	$ 278,016	$ 159,052
Gross Unrealized Gains	2,713	237
Gross Unrealized Losses	(35)	(202)
Estimated Fair Value	280,694	159,087
Corporate bonds
Schedule of Investments [Line Items]
Amortized Cost	23,415	69,947
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(56)
Estimated Fair Value	23,409	69,891
Certificates of deposit
Schedule of Investments [Line Items]
Amortized Cost	43,884	28,039
Gross Unrealized Gains	29	1
Gross Unrealized Losses	(6)	(62)
Estimated Fair Value	43,907	27,978
U.S. Treasury securities
Schedule of Investments [Line Items]
Amortized Cost	205,173	48,279
Gross Unrealized Gains	38	0
Gross Unrealized Losses	(23)	(82)
Estimated Fair Value	205,188	48,197
Commercial paper
Schedule of Investments [Line Items]
Amortized Cost	3,999	11,242
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(2)
Estimated Fair Value	3,999	11,240
Preferred stock of U.S. corporation
Schedule of Investments [Line Items]
Amortized Cost	1,545	1,545
Gross Unrealized Gains	2,646	236
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 4,191	$ 1,781

Investments - Schedule of Investment Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Maturing in one year or less	$ 126,364
Maturing after one year through two years	150,139
Total debt investments	276,503
Estimated Fair Value	$ 280,694	$ 159,087

Loan Payable (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended	30 Months Ended	32 Months Ended
Loan Payable (Details) - USD ($) $ in Millions	Feb. 28, 2013	Dec. 31, 2012	Jun. 30, 2015	Oct. 31, 2015	Jan. 27, 2012
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity					$ 15.0
Outstanding Principal Balance			$ 1.5
First tranche
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity					3.0
Interest only period		12 months
Principal and interest amortization period			30 months
Loan and security agreement, interest rate			8.25%
Second tranche
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity					$ 12.0
Interest only period	6 months
Scenario, Forecast [Member] \| Second tranche
Line of Credit Facility [Line Items]
Principal and interest amortization period				32 months
Loan and security agreement, interest rate				8.25%

Equity Transactions and Share-based Compensation Common Stock Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	Jun. 16, 2015	Jun. 30, 2015	Jun. 30, 2014
Class of Stock [Line Items]
Proceeds from public offering, net of offering costs		$ 161,880	$ 111,845
Common Stock [Member]
Class of Stock [Line Items]
Shares Issued, Price Per Share	$ 39.75
Proceeds from public offering, net of offering costs	$ 161,900
Public Offering [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	4,341,250
Over-Allotment Option [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	566,250

Income Taxes (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
Income Taxes (Narrative) (Details) - USD ($)	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2015
Income Tax Contingency [Line Items]
Federal or state income taxes	$ 0	$ 0	$ 0	$ 0
Unrecognized Tax Benefits	$ 0		$ 0
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Estimated annual effective tax rate					0.00%