Chimerix (CMRX) 10-Q 8 Nov 17 2017 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Nov. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Entity Registrant Name	CHIMERIX INC
Entity Central Index Key	1,117,480
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		47,127,732

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 18,173	$ 51,463
Short-term investments, available-for-sale	131,547	180,558
Accounts receivable	270	1,599
Prepaid expenses and other current assets	2,600	2,845
Total current assets	152,590	236,465
Long-term investments	91,419	47,407
Property and equipment, net of accumulated depreciation	2,044	2,843
Other long-term assets	32	55
Total assets	246,085	286,770
Current liabilities:
Accounts payable	1,571	3,890
Accrued liabilities	7,416	6,215
Total current liabilities	8,987	10,105
Lease-related obligations	199	441
Total liabilities	9,186	10,546
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized at September 30, 2017 and December 31, 2016; no shares issued and outstanding as of September 30, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value, 200,000,000 shares authorized at September 30, 2017 and December 31, 2016; 47,127,732 and 46,522,475 shares issued and outstanding as of September 30, 2017 and December 31, 2016, respectively	47	46
Additional paid-in capital	705,883	692,422
Accumulated other comprehensive loss, net	(1,481)	(440)
Accumulated deficit	(467,550)	(415,804)
Total stockholders’ equity	236,899	276,224
Total liabilities and stockholders’ equity	$ 246,085	$ 286,770

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	47,127,732	46,522,475
Common stock, shares outstanding (in shares)	47,127,732	46,522,475

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Contract revenue	$ 897	$ 653	$ 2,650	$ 3,722
Operating expenses:
Research and development	12,157	12,247	36,535	46,942
General and administrative	6,650	5,827	19,530	19,359
Total operating expenses	18,807	18,074	56,065	66,301
Loss from operations	(17,910)	(17,421)	(53,415)	(62,579)
Interest income	598	396	1,669	1,146
Net loss	(17,312)	(17,025)	(51,746)	(61,433)
Other comprehensive loss:
Unrealized (loss) gain on investments, net	(6)	(98)	(1,041)	398
Comprehensive loss	$ (17,318)	$ (17,123)	$ (52,787)	$ (61,035)
Per share information:
Net loss, basic and diluted (in dollars per share)	$ (0.37)	$ (0.37)	$ (1.10)	$ (1.33)
Weighted-average shares outstanding, basic and diluted (in shares)	47,065,756	46,236,749	46,836,099	46,211,748

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (51,746)	$ (61,433)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	828	781
Amortization of premium/discount on investments	49	1,010
Share-based compensation	12,478	12,334
Amortization of lease-related obligations	(298)	(51)
Changes in operating assets and liabilities:
Accounts receivable	1,328	2,080
Prepaid expenses and other assets	268	1,741
Accounts payable and accrued liabilities	(909)	(10,580)
Net cash used in operating activities	(38,002)	(54,118)
Cash flows from investing activities:
Purchases of property and equipment	(30)	(763)
Purchases of short-term investments	0	(13,990)
Purchases of long-term investments	(144,536)	(50,867)
Proceeds from sales of short-term investments	4,000	0
Proceeds from maturities of short-term investments	144,445	147,899
Net cash provided by investing activities	3,879	82,279
Cash flows from financing activities:
Proceeds from exercise of stock options	121	152
Proceeds from employee stock purchase plan	712	440
Net cash provided by financing activities	833	592
Net (decrease) increase in cash and cash equivalents	(33,290)	28,753
Cash and cash equivalents:
Beginning of period	51,463	20,605
End of period	$ 18,173	$ 49,358

The Business and Summary of Sig

The Business and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
The Business and Summary of Significant Accounting Policies	The Business and Summary of Significant Accounting Policies Description of Business Chimerix, Inc. (the Company) is a biopharmaceutical company committed to discovering, developing and commercializing medicines that improve outcomes for immunocompromised patients. The Company was founded in 2000 based on the promise of our proprietary lipid conjugate technology to unlock the potential of some of the most broad-spectrum antivirals by enhancing their antiviral activity and safety profiles in convenient dosing regimens. The Company's lead compound, brincidofovir, is in development as an oral and intravenous (IV) formulation for the prevention and treatment of DNA viruses, including smallpox, adenoviruses, and the human herpesviruses. The Company is also advancing the development of CMX521 for the treatment and prevention of norovirus. In addition, the Company has an active discovery program focusing on viral targets for which limited or no therapies are currently available. Basis of Presentation The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (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, 2016 . 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 nine months ended September 30, 2017 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. 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. In June 2016, the Company's preferred stock investment in ContraVir Pharmaceuticals (NASDAQ: CTRV) (ContraVir) was transferred from Level 3 to Level 2. In September 2016, the Company's investment in ContraVir was transferred from Level 2 to Level 1. See below for further discussion. There were no transfers between Level 1 and Level 2 and no transfers to or from Level 3 during the nine months ended September 30, 2017 . At September 30, 2017 and December 31, 2016 , 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 September 30, 2017 and December 31, 2016 , the Company had cash equivalents consisting of commercial paper. At December 31, 2016, the Company had short-term investments consisting of brokered certificates of deposit. As quoted prices are not available for these securities, they 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. In December 2014, the Company entered into a license agreement with ContraVir for the development and commercialization of CMX157 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 ContraVir Series B Convertible Preferred Stock. On September 30, 2016, the Company converted its preferred stock investment in ContraVir into 1,071,429 shares of ContraVir common stock. The Company's investment in ContraVir common stock was categorized as a Level 1 asset and valued based on ContraVir's common stock value at September 30, 2017 and December 31, 2016 . 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. For additional information regarding the Company's investments, please refer to Note 2, "Investments." Below is a table that presents information about certain assets measured at fair value on a recurring basis (in thousands): Fair Value Measurements September 30, 2017 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 11,601 $ 11,601 $ — $ — Commercial paper 5,999 — 5,999 — Total cash equivalents 17,600 11,601 5,999 — Short-term investments U.S. treasury securities 130,979 130,979 — — Common stock of U.S. corporation 568 568 — — Total short-term investments 131,547 131,547 — — Long-term investments U.S. treasury securities 91,419 91,419 — — Total long-term investments 91,419 91,419 — — Total assets $ 240,566 $ 234,567 $ 5,999 $ — Fair Value Measurements December 31, 2016 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 15,733 $ 15,733 $ — $ — Commercial paper 35,097 — 35,097 — Total cash equivalents 50,830 15,733 35,097 — Short-term investments Certificates of deposit 7,450 — 7,450 — U.S. treasury securities 171,822 171,822 — — Common stock of U.S. corporation 1,286 1,286 — — Total short-term investments 180,558 173,108 7,450 — Long-term investments U.S. treasury securities 47,407 47,407 — — Total long-term investments 47,407 47,407 — — Total assets $ 278,795 $ 236,248 $ 42,547 $ — Accrued Liabilities Accrued liabilities consisted of the following (in thousands): September 30, 2017 December 31, 2016 Accrued research and development expenses $ 2,749 $ 2,257 Accrued compensation 3,067 2,906 Other accrued liabilities 1,600 1,052 Total accrued liabilities $ 7,416 $ 6,215 Revenue Recognition The Company’s revenues generally consist of (i) contract revenue – revenue generated under federal contracts, and (ii) collaboration and licensing revenue – revenue related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenue is recognized in accordance with the criteria outlined in the Securities and Exchange Commission (SEC)’s Topic 13 and Accounting Standards Codification (ASC) 605-25 issued by the Financial Accounting Standards Board (FASB). Following these accounting pronouncements, revenue is recognized when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred and risk of loss has passed; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. The Company recognizes revenue under government contracts as qualifying research activities are conducted based on invoices received. 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 and 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 its research and development efforts. 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 research and development 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 its research and development efforts. The Company determines prepaid and accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of clinical trials, or other services completed. The Company adjusts its rate of research and development expense recognition if actual results differ from its estimates. The Company makes estimates of its prepaid and 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 September 30, 2017 , there had been no material adjustments to the Company’s prior period estimates of prepaid and accruals for research and development expenses. The Company’s research and development prepaids and accruals are dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors. Basic and Diluted Net Loss Per Share of Common Stock Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of warrants to purchase common stock, non-vested restricted stock, stock options, and employee stock purchase plan purchase rights. Diluted net loss per share of common stock is computed by dividing net loss by the sum of the weighted-average number of shares of common stock outstanding during the period plus the potential dilutive effects of warrants to purchase common stock, non-vested restricted stock, stock options, and employee stock purchase plan purchase rights 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 and nine months ended September 30, 2017 and 2016 . The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of warrants to purchase common stock, non-vested restricted stock, stock options to purchase common stock, and employee stock purchase plan purchase rights as the impact of such items are anti-dilutive during periods of net loss. Potential common shares excluded from the calculations were 1.6 million and 1.4 million for the three months ended September 30, 2017 and 2016 , respectively, and 1.8 million and 0.9 million for the nine months ended September 30, 2017 and 2016 , respectively. Impact of Recently Issued Accounting Standards In May 2014, the FASB issued Accounting Standards Update (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. The FASB has issued several updates to the standard which (1) defer the original effective date to annual periods and interim periods within those annual periods beginning after December 15, 2017, while allowing for early adoption as of January 1, 2017 (ASU 2015-14); (2) clarify the application of the principal versus agent guidance (ASU 2016-08); and (3) clarify the guidance on inconsequential and perfunctory promises and licensing (ASU 2016-10). The Company has evaluated its contract with the Biomedical Advanced Research and Development Authority (BARDA) and license agreement with ContraVir, and does not anticipate that the adoption of the ASU will have a material impact on its consolidated financial statements. The Company plans to use the full retrospective method of adoption effective January 1, 2018. In January 2016, the FASB issued ASU No. 2016-01, “Financial Instruments-Overall (Subtopic 825-10)-Recognition and Measurement of Financial Assets and Financial Liabilities.” The new standard enhances reporting for financial instruments. The ASU is effective for financial statements issued for annual periods and interim periods within those annual periods beginning after December 15, 2017. Earlier adoption is permitted for interim and annual reporting periods as of the beginning of the fiscal year of adoption. The Company does not expect the adoption of ASU 2016-01 to have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)”, which increases transparency and comparability among companies accounting for lease transactions. The most significant change of this update will require the recognition of lease assets and liabilities on the balance sheet for lessees for operating lease arrangements with lease terms greater than 12 months. This update will require a modified retrospective application which includes a number of optional practical expedients related to the identification and classification of leases commenced before the effective date. This ASU is effective for financial statements issued for annual periods and interim periods within those annual periods, beginning after December 15, 2018. The Company is currently analyzing the impact of the adoption of ASU No. 2016-02 on its consolidated financial statements. Impact of Recently Adopted Accounting Standards In March 2016, the FASB issued ASU No. 2016-09, "Improvements to Employee Share-Based Payment Accounting", which simplifies several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The ASU is effective for financial statements issued for annual periods and interim periods within those annual periods, beginning after December 15, 2016, with early adoption permitted. ASU No. 2016-09 became effective for the Company beginning in the first quarter of 2017. The Company elected to continue estimating the number of awards expected to be forfeited and adjusting the estimate when it is no longer probable that the employee will fulfill the service condition. The Company's adoption of ASU No. 2016-09 did not have a material impact on its consolidated financial statements.

Investments

Investments	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	Investments The following tables summarize the Company's short-term and long-term investments (in thousands): September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury securities $ 222,902 $ — $ (504 ) $ 222,398 Common stock of U.S. corporation 1,545 — (977 ) 568 Total investments $ 224,447 $ — $ (1,481 ) $ 222,966 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Certificates of deposit $ 7,445 $ 5 $ — $ 7,450 U.S. treasury securities 219,415 15 (201 ) 219,229 Common stock of U.S. corporation 1,545 — (259 ) 1,286 Total investments $ 228,405 $ 20 $ (460 ) $ 227,965 The following tables summarize the Company's investments with unrealized losses, aggregated by investment type and the length of time that individual investments have been in a continuous unrealized loss position (in thousands, except number of securities): September 30, 2017 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. treasury securities $ 189,449 $ (430 ) $ 32,949 $ (74 ) $ 222,398 $ (504 ) Common stock of U.S. corporation 568 (977 ) — — 568 (977 ) Total $ 190,017 $ (1,407 ) $ 32,949 $ (74 ) $ 222,966 $ (1,481 ) Number of securities with unrealized losses 41 7 48 December 31, 2016 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. treasury securities $ 128,204 $ (201 ) $ — $ — $ 128,204 $ (201 ) Common stock of U.S. corporation 1,286 (259 ) — — 1,286 (259 ) Total $ 129,490 $ (460 ) $ — $ — $ 129,490 $ (460 ) Number of securities with unrealized losses 24 — 24 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. The Company evaluates, among other things, the duration and extent to which the fair value of a security is less than its cost; the financial condition of the issuer and any changes thereto; and the Company’s intent to sell, or whether it will more likely than not be required to sell, the security before recovery of its cost basis. At September 30, 2017 , the Company did not intend to sell, and was not more likely than not to be required to sell, the available-for-sale securities in an unrealized loss position before recovery of the cost basis of the securities, which may be at maturity. There were no such declines in value for the three and nine months ended September 30, 2017 and 2016 . Unrealized gains and losses on investments are recorded to unrealized (loss) gain on investments, net in the Consolidated Statements of Operations and Comprehensive Loss. The Company recognizes interest income on an accrual basis in interest income in the Consolidated Statements of Operations and Comprehensive Loss. The following table summarizes the scheduled maturity for the Company's debt investments at September 30, 2017 (in thousands): Maturing in one year or less $ 130,979 Maturing after one year through two years 91,419 Total debt investments 222,398 Common stock of U.S. corporation 568 Total investments $ 222,966

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
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 $0.1 million and $0.2 million for the three months ended September 30, 2017 and 2016 , respectively, and $0.4 million and $0.6 million for the nine months ended September 30, 2017 and 2016 , respectively. Significance of Revenue Source The Company is the recipient of federal research contract funds from BARDA, the sole 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 had been made as of September 30, 2017 and December 31, 2016 .

Equity Transactions and Share-b

Equity Transactions and Share-based Compensation	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Transactions and Share-based Compensation	Equity Transactions and Share-based Compensation Warrants For the three and nine months ended September 30, 2017 , there were no exercises of warrants for the purchase of shares of the Company's common stock. 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), non-statutory 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, 2017 , the common stock reserved for issuance under the 2013 Plan was automatically increased by 1.9 million shares. As of September 30, 2017 , there was a total of 1.0 million shares reserved for future issuance under the 2013 Plan. The Company issued approximately 5,000 and 32,000 shares of common stock pursuant to the exercise of stock options for the three and nine months ended September 30, 2017 , respectively. 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, 2017 , the common stock reserved for issuance under the ESPP was automatically increased by an additional 0.4 million shares. The Company has reserved a total of 2.2 million shares of common stock to be purchased under the ESPP, of which 1.9 million shares remained available for purchase as of September 30, 2017 . The ESPP 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. Eligible employees may authorize an amount up to 15% of their salary to purchase common stock at the lower of a 15% discount to the beginning price of their offering period or a 15% discount to the ending price of each six-month purchase interval. The Company issued approximately 80,000 shares of common stock pursuant to the ESPP for the three months ended September 30, 2017 . The Company issued approximately 174,000 shares of common stock pursuant to the ESPP for the nine months ended September 30, 2017 . Compensation expense for shares purchased under the ESPP related to the purchase discount and the “look-back” option and were determined using a Black-Scholes option pricing model. Restricted Stock Units In January 2017 and May 2016, the Company issued RSUs to certain employees which vest based on service criteria. When vested, the RSU represents the right to be issued the number of shares of the Company's common stock that is equal to the number of RSUs granted. The grant date fair value for RSUs is based upon the market price of the Company's common stock on the date of the grant. The fair value is then amortized to compensation expense over the requisite service period or vesting term. The Company issued no shares of common stock pursuant to the vesting of RSUs for the three months ended September 30, 2017 , and 366,650 shares of common stock pursuant to the vesting of RSUs for the nine months ended September 30, 2017 . In January 2017, the Company also granted performance-based RSUs which, when vested, represent the right to be issued the number of shares of the Company’s common stock that is equal to the number of RSUs granted. The grant date fair value for performance-based RSUs is based upon the market price of the Company’s common stock on the date of the grant. For the portion of the performance-based RSUs of which the achievement of the performance condition is considered probable, the Company recognizes stock-based compensation expense on the related estimated fair value of such RSUs ratably for each vesting tranche from the service inception date to the end of the requisite service period. For the performance conditions that are not considered probable of achievement at the grant date or upon quarterly re-evaluation, prior to the event actually occurring, the Company begins recognizing the related stock-based compensation expense ratably when the event occurs or when the Company can determine that achievement of the performance condition is probable. In those cases, the Company recognizes the change in estimate at the time it determines the performance condition is probable of achievement (by recognizing stock-based compensation expense as cumulative catch-up adjustment as if the Company had estimated at the grant date that the performance condition would have been achieved) and recognize the remaining compensation cost through the end of the requisite service period. The Company issued no shares of common stock pursuant to the vesting of performance-based RSUs for the three and nine months ended September 30, 2017 . 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. Employee and non-employee share-based compensation expense recognized related to stock options, the ESPP and RSUs was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 Research and development expense: Employee $ 1,852 $ 1,942 $ 5,462 $ 5,373 Non-employee 1 — 6 — General and administrative expense: Employee 2,365 2,153 7,010 6,961 Non-employee — — — — Total share-based compensation expense $ 4,218 $ 4,095 $ 12,478 $ 12,334

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company estimates an annual effective tax rate of 0% for the year ending December 31, 2017 as the Company incurred losses for the nine month period ended September 30, 2017 and is forecasting additional losses through the fourth quarter of 2017, resulting in an estimated net loss for both financial statement and tax purposes for the year ending December 31, 2017 . 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 full valuation allowance, since the Company does not currently believe that realization of its deferred tax assets is more likely than not. At September 30, 2017 , the Company had no unrecognized tax benefits that would reduce the Company’s effective tax rate if recognized.

Significant Agreements

Significant Agreements	9 Months Ended
	Sep. 30, 2017
Revenue Recognition [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. 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. 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), 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 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 nine months ended September 30, 2017 and 2016 . Biomedical Advanced Research and Development Authority (BARDA) In February 2011, the Company entered into a contract with BARDA for the advanced development of brincidofovir as a medical countermeasure in the event of a smallpox release. Under the contract, BARDA will reimburse the Company, plus pay a fixed fee, for the research and development of brincidofovir as a broad-spectrum therapeutic antiviral for the treatment of smallpox infections. The contract consists of an initial performance period, referred to as the base performance segment, plus up to four extension periods, 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 second and third option segments of the contract during which the Company may receive up to a total of $17.5 million and $13 million in expense reimbursement and fees, respectively. The second and third option segments are expected to end on December 8, 2017. For the three months ended September 30, 2017 and 2016 , the Company recognized revenue under this contract of $0.9 million and $0.7 million , respectively, and for the nine months ended September 30, 2017 and 2016 , the Company recognized revenue under this contract of $2.7 million and $3.7 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 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 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 sixty 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. 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 completion of the transfer of the IND and technical know-how related to CMX157 in April 2015, the Company recognized the $1.5 million upfront payment as revenue. In September 2016, the Company converted its shares of ContraVir Series B convertible preferred stock into 1,071,429 shares of ContraVir common stock. As of September 30, 2017 and December 31, 2016 , the fair value of the investment was recorded as a short-term investment of $0.6 million and $1.3 million , respectively. University of Michigan In 2006, the Company entered into a license agreement with The Regents of the University of Michigan (UM) under which the Company obtained an exclusive, worldwide license to UM’s patent rights in certain inventions (UM Patent Rights) related to certain compounds originally synthesized at UM. Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UM Patent Rights, and to sublicense such rights subject to certain sublicensing fees and royalty payments. In consideration for the rights granted to the Company, under the license agreement as amended in December 2016, the Company paid UM $50,000 in fees in 2016 and in January 2017 issued UM an aggregate of 33,058 shares of its common stock. In connection with the Company's commercialization or sublicensing of certain products covered by the license agreement, including CMX521, the Company could be required to pay royalties on net sales of such products ranging from 0.25% to 2% . Beginning in 2024, the Company is also subject to certain minimum annual royalty payments. The UM license agreement requires that the Company uses commercially reasonable efforts to develop and make commercially available licensed products as soon as practicable. Specifically, the Company has agreed to make the first commercial sale of a licensed product by June of 2026. UM may terminate the license agreement if the Company materially breaches the license agreement. The Company is currently in compliance with its milestone requirements.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2017
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 September 30, 2017 , and events which occurred subsequently but were not recognized in the financial statements.

The Business and Summary of S13

The Business and Summary of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (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, 2016 . 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 nine months ended September 30, 2017 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	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. 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.
Revenue Recognition	Revenue Recognition The Company’s revenues generally consist of (i) contract revenue – revenue generated under federal contracts, and (ii) collaboration and licensing revenue – revenue related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenue is recognized in accordance with the criteria outlined in the Securities and Exchange Commission (SEC)’s Topic 13 and Accounting Standards Codification (ASC) 605-25 issued by the Financial Accounting Standards Board (FASB). Following these accounting pronouncements, revenue is recognized when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred and risk of loss has passed; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. The Company recognizes revenue under government contracts as qualifying research activities are conducted based on invoices received. 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 and 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	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 its research and development efforts. 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 research and development 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 its research and development efforts. The Company determines prepaid and accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of clinical trials, or other services completed. The Company adjusts its rate of research and development expense recognition if actual results differ from its estimates. The Company makes estimates of its prepaid and 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 September 30, 2017 , there had been no material adjustments to the Company’s prior period estimates of prepaid and accruals for research and development expenses. The Company’s research and development prepaids and accruals are dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.
Basic and Diluted Net Loss Per Share of Common Stock	Basic and Diluted Net Loss Per Share of Common Stock Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of warrants to purchase common stock, non-vested restricted stock, stock options, and employee stock purchase plan purchase rights. Diluted net loss per share of common stock is computed by dividing net loss by the sum of the weighted-average number of shares of common stock outstanding during the period plus the potential dilutive effects of warrants to purchase common stock, non-vested restricted stock, stock options, and employee stock purchase plan purchase rights 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 and nine months ended September 30, 2017 and 2016 . The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of warrants to purchase common stock, non-vested restricted stock, stock options to purchase common stock, and employee stock purchase plan purchase rights as the impact of such items are anti-dilutive during periods of net loss.
Impact of Recently Issued Accounting Standards and Impact of Recently Adopted Accounting Standards	Impact of Recently Issued Accounting Standards In May 2014, the FASB issued Accounting Standards Update (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. The FASB has issued several updates to the standard which (1) defer the original effective date to annual periods and interim periods within those annual periods beginning after December 15, 2017, while allowing for early adoption as of January 1, 2017 (ASU 2015-14); (2) clarify the application of the principal versus agent guidance (ASU 2016-08); and (3) clarify the guidance on inconsequential and perfunctory promises and licensing (ASU 2016-10). The Company has evaluated its contract with the Biomedical Advanced Research and Development Authority (BARDA) and license agreement with ContraVir, and does not anticipate that the adoption of the ASU will have a material impact on its consolidated financial statements. The Company plans to use the full retrospective method of adoption effective January 1, 2018. In January 2016, the FASB issued ASU No. 2016-01, “Financial Instruments-Overall (Subtopic 825-10)-Recognition and Measurement of Financial Assets and Financial Liabilities.” The new standard enhances reporting for financial instruments. The ASU is effective for financial statements issued for annual periods and interim periods within those annual periods beginning after December 15, 2017. Earlier adoption is permitted for interim and annual reporting periods as of the beginning of the fiscal year of adoption. The Company does not expect the adoption of ASU 2016-01 to have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)”, which increases transparency and comparability among companies accounting for lease transactions. The most significant change of this update will require the recognition of lease assets and liabilities on the balance sheet for lessees for operating lease arrangements with lease terms greater than 12 months. This update will require a modified retrospective application which includes a number of optional practical expedients related to the identification and classification of leases commenced before the effective date. This ASU is effective for financial statements issued for annual periods and interim periods within those annual periods, beginning after December 15, 2018. The Company is currently analyzing the impact of the adoption of ASU No. 2016-02 on its consolidated financial statements. Impact of Recently Adopted Accounting Standards In March 2016, the FASB issued ASU No. 2016-09, "Improvements to Employee Share-Based Payment Accounting", which simplifies several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The ASU is effective for financial statements issued for annual periods and interim periods within those annual periods, beginning after December 15, 2016, with early adoption permitted. ASU No. 2016-09 became effective for the Company beginning in the first quarter of 2017. The Company elected to continue estimating the number of awards expected to be forfeited and adjusting the estimate when it is no longer probable that the employee will fulfill the service condition. The Company's adoption of ASU No. 2016-09 did not have a material impact on its consolidated financial statements.

The Business and Summary of S14

The Business and Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Schedule of certain assets measured at fair value on a recurring basis	Below is a table that presents information about certain assets measured at fair value on a recurring basis (in thousands): Fair Value Measurements September 30, 2017 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 11,601 $ 11,601 $ — $ — Commercial paper 5,999 — 5,999 — Total cash equivalents 17,600 11,601 5,999 — Short-term investments U.S. treasury securities 130,979 130,979 — — Common stock of U.S. corporation 568 568 — — Total short-term investments 131,547 131,547 — — Long-term investments U.S. treasury securities 91,419 91,419 — — Total long-term investments 91,419 91,419 — — Total assets $ 240,566 $ 234,567 $ 5,999 $ — Fair Value Measurements December 31, 2016 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 15,733 $ 15,733 $ — $ — Commercial paper 35,097 — 35,097 — Total cash equivalents 50,830 15,733 35,097 — Short-term investments Certificates of deposit 7,450 — 7,450 — U.S. treasury securities 171,822 171,822 — — Common stock of U.S. corporation 1,286 1,286 — — Total short-term investments 180,558 173,108 7,450 — Long-term investments U.S. treasury securities 47,407 47,407 — — Total long-term investments 47,407 47,407 — — Total assets $ 278,795 $ 236,248 $ 42,547 $ —
Schedule of accrued liabilities	Accrued liabilities consisted of the following (in thousands): September 30, 2017 December 31, 2016 Accrued research and development expenses $ 2,749 $ 2,257 Accrued compensation 3,067 2,906 Other accrued liabilities 1,600 1,052 Total accrued liabilities $ 7,416 $ 6,215

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of short-term and long-term investments	The following tables summarize the Company's short-term and long-term investments (in thousands): September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value U.S. treasury securities $ 222,902 $ — $ (504 ) $ 222,398 Common stock of U.S. corporation 1,545 — (977 ) 568 Total investments $ 224,447 $ — $ (1,481 ) $ 222,966 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Certificates of deposit $ 7,445 $ 5 $ — $ 7,450 U.S. treasury securities 219,415 15 (201 ) 219,229 Common stock of U.S. corporation 1,545 — (259 ) 1,286 Total investments $ 228,405 $ 20 $ (460 ) $ 227,965
Summary of investments with unrealized losses, aggregated by investment type and the length of time	The following tables summarize the Company's investments with unrealized losses, aggregated by investment type and the length of time that individual investments have been in a continuous unrealized loss position (in thousands, except number of securities): September 30, 2017 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. treasury securities $ 189,449 $ (430 ) $ 32,949 $ (74 ) $ 222,398 $ (504 ) Common stock of U.S. corporation 568 (977 ) — — 568 (977 ) Total $ 190,017 $ (1,407 ) $ 32,949 $ (74 ) $ 222,966 $ (1,481 ) Number of securities with unrealized losses 41 7 48 December 31, 2016 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. treasury securities $ 128,204 $ (201 ) $ — $ — $ 128,204 $ (201 ) Common stock of U.S. corporation 1,286 (259 ) — — 1,286 (259 ) Total $ 129,490 $ (460 ) $ — $ — $ 129,490 $ (460 ) Number of securities with unrealized losses 24 — 24
Summary of the scheduled maturity of Company investments	The following table summarizes the scheduled maturity for the Company's debt investments at September 30, 2017 (in thousands): Maturing in one year or less $ 130,979 Maturing after one year through two years 91,419 Total debt investments 222,398 Common stock of U.S. corporation 568 Total investments $ 222,966

Equity Transactions and Share16

Equity Transactions and Share-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of employee and non-employee share-based compensation expense recognized related to stock options, the ESPP and RSUs	Employee and non-employee share-based compensation expense recognized related to stock options, the ESPP and RSUs was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 Research and development expense: Employee $ 1,852 $ 1,942 $ 5,462 $ 5,373 Non-employee 1 — 6 — General and administrative expense: Employee 2,365 2,153 7,010 6,961 Non-employee — — — — Total share-based compensation expense $ 4,218 $ 4,095 $ 12,478 $ 12,334

The Business and Summary of S17

The Business and Summary of Significant Accounting Policies - Narrative (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Anti-dilutive securities excluded from the calculation loss per share (in shares)	1,600,000	1,400,000	1,800,000	900,000
Common stock of U.S. corporation | Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Convertible preferred stock, shares issued upon conversion (in shares)		1,071,429		1,071,429

The Business and Summary of S18

The Business and Summary of Significant Accounting Policies - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments	$ 131,547	$ 180,558
Long-term investments	91,419	47,407
Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents	17,600	50,830
Short-term investments	131,547	180,558
Long-term investments	91,419	47,407
Total assets	240,566	278,795
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 equivalents	11,601	15,733
Short-term investments	131,547	173,108
Long-term investments	91,419	47,407
Total assets	234,567	236,248
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 equivalents	5,999	35,097
Short-term investments	0	7,450
Long-term investments	0	0
Total assets	5,999	42,547
Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Long-term investments	0	0
Total assets	0	0
Money market funds | Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents	11,601	15,733
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 equivalents	11,601	15,733
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 equivalents	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 equivalents	0	0
Commercial paper | Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents	5,999	35,097
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 equivalents	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 equivalents	5,999	35,097
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 equivalents	0	0
Certificates of deposit | Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments		7,450
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]
Short-term investments		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]
Short-term investments		7,450
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]
Short-term investments		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	130,979	171,822
Long-term investments	91,419	47,407
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	130,979	171,822
Long-term investments	91,419	47,407
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	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	0	0
Long-term investments	0	0
Common 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	568	1,286
Common 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	568	1,286
Common 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	0	0
Common 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	$ 0	$ 0

The Business and Summary of S19

The Business and Summary of Significant Accounting Policies - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accrued research and development expenses	$ 2,749	$ 2,257
Accrued compensation	3,067	2,906
Other accrued liabilities	1,600	1,052
Total accrued liabilities	$ 7,416	$ 6,215

Investments - Summary of Availa

Investments - Summary of Available-for-Sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Amortized Cost	$ 224,447	$ 228,405
Gross Unrealized Gains	0	20
Gross Unrealized Losses	(1,481)	(460)
Estimated Fair Value	222,966	227,965
Certificates of deposit
Schedule of Investments [Line Items]
Amortized Cost		7,445
Gross Unrealized Gains		5
Gross Unrealized Losses		0
Estimated Fair Value		7,450
U.S. treasury securities
Schedule of Investments [Line Items]
Amortized Cost	222,902	219,415
Gross Unrealized Gains	0	15
Gross Unrealized Losses	(504)	(201)
Estimated Fair Value	222,398	219,229
Common stock of U.S. corporation
Schedule of Investments [Line Items]
Amortized Cost	1,545	1,545
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(977)	(259)
Estimated Fair Value	$ 568	$ 1,286

Investments - Summary of Invest

Investments - Summary of Investments with Unrealized Losses, Aggregated by Investment Type and the Length of Time (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)security	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)security	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)security
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 190,017,000		$ 190,017,000		$ 129,490,000
Unrealized Loss, Less than 12 Months	(1,407,000)		(1,407,000)		(460,000)
Fair Value, Greater than 12 Months	32,949,000		32,949,000		0
Unrealized Loss, Greater than 12 Months	(74,000)		(74,000)		0
Fair Value, Total	222,966,000		222,966,000		129,490,000
Unrealized Loss, Total	$ (1,481,000)		$ (1,481,000)		$ (460,000)
Number of securities with unrealized losses, Less than 12 Months | security	41		41		24
Number of securities with unrealized losses, Greater than 12 Months | security	7		7		0
Number of securities with unrealized losses, Total | security	48		48		24
Other than temporary impairment, investments, available-for-sale	$ 0	$ 0	$ 0	$ 0
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	189,449,000		189,449,000		$ 128,204,000
Unrealized Loss, Less than 12 Months	(430,000)		(430,000)		(201,000)
Fair Value, Greater than 12 Months	32,949,000		32,949,000		0
Unrealized Loss, Greater than 12 Months	(74,000)		(74,000)		0
Fair Value, Total	222,398,000		222,398,000		128,204,000
Unrealized Loss, Total	(504,000)		(504,000)		(201,000)
Common stock of U.S. corporation
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	568,000		568,000		1,286,000
Unrealized Loss, Less than 12 Months	(977,000)		(977,000)		(259,000)
Fair Value, Greater than 12 Months	0		0		0
Unrealized Loss, Greater than 12 Months	0		0		0
Fair Value, Total	568,000		568,000		1,286,000
Unrealized Loss, Total	$ (977,000)		$ (977,000)		$ (259,000)

Investments - Schedule of Inves

Investments - Schedule of Investment Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Maturing in one year or less	$ 130,979
Maturing after one year through two years	91,419
Total debt investments	222,398
Common stock of U.S. corporation	568
Total investments	222,966	$ 227,965
Common stock of U.S. corporation
Schedule of Available-for-sale Securities [Line Items]
Total investments	$ 568	$ 1,286

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Operating leases, rent expense	$ 100,000	$ 200,000	$ 400,000	$ 600,000
BARDA
Other Commitments [Line Items]
Deferred revenue	$ 0		$ 0		$ 0

Equity Transactions and Share24

Equity Transactions and Share-based Compensation (Details) - shares	Jan. 01, 2017	Sep. 30, 2017	Sep. 30, 2017	Feb. 28, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award, gross (in shares)		0	366,650
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 (in shares)	1,900,000
Number of shares reserved for future issuance (in shares)		1,000,000	1,000,000
Shares issued pursuant to the exercise of stock options (in shares)		5,000	32,000
The 2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, evergreen option provision, equity increase			1.00%
Additional shares authorized (in shares)	400,000
Number of shares reserved for future issuance (in shares)		1,900,000	1,900,000
Number of shares authorized to be granted (in shares)		2,200,000	2,200,000	704,225
Number of shares reserved for issuance, annual increase (in shares)			422,535
Employee stock purchase plan, automatic reset purchase period			24 months
Percentage of pay that employee can contribute, maximum		15.00%	15.00%
Employee stock purchase plan, purchase period			6 months
Discounted purchase price from market price, offering date			15.00%
Discounted purchase price from market price, purchase date			15.00%
Shares issued pursuant to employee stock purchase plan (in shares)		80,000	174,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award, gross (in shares)		0	0
Common stock of U.S. corporation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for warrants exercised (in shares)		0	0

Equity Transactions and Share25

Equity Transactions and Share-based Compensation - Schedule of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 4,218	$ 4,095	$ 12,478	$ 12,334
Employee | Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	1,852	1,942	5,462	5,373
Employee | General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	2,365	2,153	7,010	6,961
Non-employee | Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	1	0	6	0
Non-employee | General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 0	$ 0	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017
Income Tax Contingency [Line Items]
Federal or state income taxes	$ 0	$ 0	$ 0	$ 0
Unrecognized tax benefits	$ 0		$ 0
Scenario, Forecast
Income Tax Contingency [Line Items]
Estimated annual effective tax rate					0.00%

Significant Agreements (Details

Significant Agreements (Details)	Dec. 17, 2014USD ($)shares	Jan. 31, 2017shares	Dec. 31, 2016USD ($)	Apr. 30, 2015USD ($)	Feb. 28, 2011extension	May 31, 2002USD ($)shares	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)shares	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)shares	Dec. 08, 2017USD ($)
Long-term Purchase Commitment [Line Items]
Operating expenses							$ 18,807,000	$ 18,074,000	$ 56,065,000	$ 66,301,000
Contract revenue							897,000	653,000	2,650,000	3,722,000
Estimated Fair Value			$ 227,965,000				222,966,000		222,966,000
The Regents of University of California
Long-term Purchase Commitment [Line Items]
Number of options outstanding, granted (in shares) | shares						64,788
Operating expenses							0	0	0	0
The Regents of University of California | Maximum
Long-term Purchase Commitment [Line Items]
Milestone payments						$ 3,400,000
Sublicense fee percentage						50.00%
Royalties percentage						50.00%
The Regents of University of California | Maximum | Brincidofovir
Long-term Purchase Commitment [Line Items]
Sublicense fee amount, payable fee percentage						5.00%
BARDA
Long-term Purchase Commitment [Line Items]
Number of extension periods | extension					4
Contract revenue							900,000	$ 700,000	2,700,000	$ 3,700,000
ContraVir Pharmaceuticals
Long-term Purchase Commitment [Line Items]
License agreement, termination notice	60 days
Licenses revenues				$ 1,500,000
ContraVir Pharmaceuticals | Maximum
Long-term Purchase Commitment [Line Items]
Collaboration and licensing revenue	$ 20,000,000
The Regents of the University of Michigan
Long-term Purchase Commitment [Line Items]
Cost of services, licenses and services			$ 50,000
Stock issued during period, shares, issued for services | shares		33,058
The Regents of the University of Michigan | Maximum
Long-term Purchase Commitment [Line Items]
Royalties percentage			2.00%
The Regents of the University of Michigan | Minimum
Long-term Purchase Commitment [Line Items]
Royalties percentage			0.25%
Preferred Stock | ContraVir Pharmaceuticals
Long-term Purchase Commitment [Line Items]
Other significant noncash transaction, shares received as consideration (in shares) | shares	120,000
Estimated Fair Value	$ 1,500,000
Preferred Stock | ContraVir Pharmaceuticals | Stated Value
Long-term Purchase Commitment [Line Items]
Other significant noncash transaction, value of consideration received	$ 1,200,000
Common stock of U.S. corporation
Long-term Purchase Commitment [Line Items]
Estimated Fair Value			$ 1,286,000				568,000		568,000
Common stock of U.S. corporation | ContraVir Pharmaceuticals
Long-term Purchase Commitment [Line Items]
Estimated Fair Value			$ 1,300,000				$ 600,000		$ 600,000
Convertible preferred stock, shares issued upon conversion (in shares) | shares								1,071,429		1,071,429
Scenario, Forecast | BARDA | Maximum
Long-term Purchase Commitment [Line Items]
Reimbursement revenue											$ 75,800,000
Fees and commissions, other											5,300,000
Scenario, Forecast | BARDA Second Option Segment | Maximum
Long-term Purchase Commitment [Line Items]
Contract revenue											17,500,000
Scenario, Forecast | BARDA Third Option Segment | Maximum
Long-term Purchase Commitment [Line Items]
Contract revenue											$ 13,000,000