Chimerix (CMRX) 10-K 2 Mar 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 23, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Entity Registrant Name	CHIMERIX INC
Entity Central Index Key	1,117,480
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 125,692,357
Entity Common Stock, Shares Outstanding		46,555,533

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 51,463	$ 20,605
Short-term investments, available-for-sale	180,558	199,729
Accounts receivable	1,599	2,432
Prepaid expenses and other current assets	2,845	6,071
Total current assets	236,465	228,837
Long-term investments	47,407	124,040
Property and equipment, net of accumulated depreciation	2,843	3,045
Other long-term assets	55	70
Total assets	286,770	355,992
Current liabilities:
Accounts payable	3,890	10,458
Accrued liabilities	6,215	9,721
Total current liabilities	10,105	20,179
Lease-related obligations	441	354
Total liabilities	10,546	20,533
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized at December 31, 2016 and 2015; no shares issued and outstanding as of December 31, 2016 and 2015	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2016 and 2015; 46,522,475 and 46,162,525 shares issued and outstanding at December 31, 2016 and 2015, respectively	46	46
Additional paid-in capital	692,422	675,591
Accumulated other comprehensive loss	(440)	(764)
Accumulated deficit	(415,804)	(339,414)
Total stockholders’ equity	276,224	335,459
Total liabilities and stockholders’ equity	$ 286,770	$ 355,992

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 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 (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	46,522,475	46,162,525
Common stock, shares, outstanding	46,522,475	46,162,525

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Contract revenue	$ 5,702	$ 9,214	$ 4,040
Collaboration and licensing revenue	0	1,548	0
Total revenues	5,702	10,762	4,040
Operating expenses:
Research and development	58,647	97,717	45,379
General and administrative	25,007	31,296	17,527
Total operating expenses	83,654	129,013	62,906
Loss from operations	(77,952)	(118,251)	(58,866)
Other income (expense):
Interest income (expense), net	1,562	879	(446)
Net loss	(76,390)	(117,372)	(59,312)
Other comprehensive loss:
Unrealized gain (loss) on investments, net	324	(799)	35
Comprehensive loss	$ (76,066)	$ (118,171)	$ (59,277)
Per share information:
Net loss, basic and diluted (in USD per share)	$ (1.65)	$ (2.67)	$ (1.80)
Weighted-average shares outstanding, basic and diluted (in shares)	46,267,064	43,878,326	33,003,714

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Common stock offering, May 27, 2014	Common stock offering, May 27, 2014Common Stock	Common stock offering, May 27, 2014Additional Paid-in Capital	Common stock offering, November 5, 2014	Common stock offering, November 5, 2014Common Stock	Common stock offering, November 5, 2014Additional Paid-in Capital
Beginning Balance at Dec. 31, 2013	$ 98,539	$ 26	$ 261,243		$ (162,730)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	4,411		4,411
Exercise of stock options	4,593	2	4,591
Exercise of warrants	6		6
Employee stock purchase plan purchases	426	1	425
Issuance of common stock, value						$ 111,845	$ 8	$ 111,837	$ 114,093	$ 4	$ 114,089
Comprehensive loss:
Unrealized gain (loss) on investments, net	35			$ 35
Net loss	(59,312)				(59,312)
Comprehensive loss	(59,277)
Ending Balance at Dec. 31, 2014	274,636	41	496,602	35	(222,042)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	12,959		12,959
Exercise of stock options	2,107		2,107
Exercise of warrants	1,001	1	1,000
Employee stock purchase plan purchases	1,048		1,048
Issuance of common stock, value	161,879	4	161,875
Comprehensive loss:
Unrealized gain (loss) on investments, net	(799)			(799)
Net loss	(117,372)				(117,372)
Comprehensive loss	(118,171)
Ending Balance at Dec. 31, 2015	335,459	46	675,591	(764)	(339,414)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	16,223		16,223
Exercise of stock options	168	0	168
Employee stock purchase plan purchases	440	0	440
Comprehensive loss:
Unrealized gain (loss) on investments, net	324			324
Net loss	(76,390)				(76,390)
Comprehensive loss	(76,066)
Ending Balance at Dec. 31, 2016	$ 276,224	$ 46	$ 692,422	$ (440)	$ (415,804)

Consolidated Statements of Sto6

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
New issues of stock during period (in shares)	4,341,250
Offering price per share (in USD per share)	$ 39.75
Stock issuance costs	$ 10,685
Common stock offering, May 27, 2014
New issues of stock during period (in shares)		8,395,000
Offering price per share (in USD per share)		$ 14.22
Stock issuance costs		$ 7,531
Common stock offering, November 5, 2014
New issues of stock during period (in shares)		4,197,500
Offering price per share (in USD per share)		$ 29
Stock issuance costs		$ 7,634

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (76,390)	$ (117,372)	$ (59,312)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	1,063	657	283
Amortization of debt costs	0	64	148
Amortization of premium/discount on investments	1,223	1,622	1,175
Share-based compensation	16,223	12,959	4,411
Amortization of lease-related obligations	132	19	(19)
Changes in operating assets and liabilities:
Accounts receivable	861	(2,354)	142
Prepaid expenses and other assets	3,215	(3,028)	(107)
Accounts payable and accrued liabilities	(10,142)	7,725	6,202
Net cash used in operating activities	(63,815)	(99,708)	(47,077)
Cash flows from investing activities:
Purchases of property and equipment	(841)	(2,393)	(1,018)
Purchases of short-term investments	(23,992)	(60,297)	(155,433)
Purchases of long-term investments	(79,381)	(234,791)	(55,337)
Sales of short-term investments	0	1,003	3,499
Maturities of short-term investments	198,279	126,742	48,589
Maturities of long-term investments	0	240	0
Net cash provided by (used in) investing activities	94,065	(169,496)	(159,700)
Cash flows from financing activities:
Proceeds from exercise of stock options	168	2,107	4,593
Proceeds from employee stock purchase plan stock purchases	440	1,048	426
Proceeds from exercise of warrants	0	1,001	6
Proceeds from public offerings, net of offering costs	0	161,879	225,938
Payments for deferred financing costs	0	(338)	0
Repayments of debt	0	(4,350)	(5,700)
Net cash provided by financing activities	608	161,347	225,263
Net increase (decrease) in cash and cash equivalents	30,858	(107,857)	18,486
Beginning of period	20,605	128,462	109,976
End of period	51,463	20,605	128,462
Supplemental disclosure of cash flow information
Cash paid for interest	0	158	614
Non-cash acquisition of investment in U.S. corporation	$ 0	$ 0	$ 1,545

The Business and Summary of Sig

The Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
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 biotechnology company committed to discovering, developing and commercializing medicines that address significant, unmet medical needs. 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 consolidated financial statements include the accounts of the Company, and its wholly owned subsidiaries. The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The preparation of the Company’s consolidated financial statements requires estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the consolidated financial statements and accompanying notes. Although these estimates are based on knowledge of current events and actions the Company may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Reclassifications Certain prior period amounts in the accompanying consolidated financial statements have been reclassified to conform to the current year presentation. These reclassifications had no effect on previously reported net income or stockholders' equity (deficit). Cash and Cash Equivalents The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market funds and commercial paper. Investments Investments consist primarily of brokered certificates of deposit, U.S. Treasury securities and stock of a U.S. corporation. The Company invests in high-credit quality investments in accordance with its investment policy which minimizes the probability of loss. Available-for-sale securities are carried at fair value as determined by quoted market prices, with the unrealized gains and losses, net of tax, reported as a separate component of stockholders equity. Realized gains and losses are determined using the specific identification method and transactions are recorded on a settlement date basis in interest income or expense, net. Investments with original maturities beyond three months at the date of purchase and which mature on, or less than twelve months from, the balance sheet date are classified as short-term. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term. The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. 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 amortized cost basis. The Company does not intend to sell, and is not likely to be required to sell, the available-for-sale securities in an unrealized loss position before recovery of the amortized cost bases of the securities, which may be maturity. Any such declines in value judged to be other-than-temporary on available-for-sale securities are reported in interest income or expense, net. There were no such declines in value for the years ended December 31, 2016 , 2015 and 2014 . The Company recognizes interest income on an accrual basis in interest income (expense), net in the Consolidated Statements of Operations and Comprehensive Loss. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, short-term investments, long-term investments and accounts receivable. The Company is exposed to credit risk, subject to federal deposit insurance, in the event of default by the financial institutions holding its cash and cash equivalents to the extent of amounts recorded on the balance sheets. Accounts receivable represent amounts due from an agency of the federal government. Accounts Receivable Accounts receivable at December 31, 2016 and December 31, 2015 consisted of amounts billed under the Company’s contract with the Biomedical Advanced Research and Development Authority (BARDA). Receivables under the BARDA contract are recorded as qualifying research activities are conducted and invoices from the Company’s vendors are received. The Company carries its accounts receivable at cost less an allowance for doubtful accounts. On a periodic basis, the Company evaluates its accounts receivable and establishes an allowance based on its history of collections and write-offs and the current status of all receivables. The Company does not accrue interest on trade receivables. If accounts become uncollectible, they will be written off through a charge to the allowance for doubtful accounts. The Company has not recorded a charge to allowance for doubtful accounts as management believes all receivables are fully collectible. Fair Value of Financial Instruments The carrying amounts of certain financial instruments, including accounts receivable, 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. There were no transfers between Level 1 and Level 2 or transfers to or from Level 3 during the year ended December 31, 2015 . When the 18 month restriction on selling the Company's investment in ContraVir Pharmaceuticals ended on June 17, 2016, the investment was transferred from Level 3 to Level 2 as the fair value was based on quoted prices for similar assets and there were no significant unobservable inputs. The Company's investment in ContraVir Pharmaceuticals transferred from Level 2 to Level 1 when the Company converted its investment in Series B Preferred shares into common stock in 2016. At December 31, 2016 and 2015 , the Company had cash equivalents, consisting of money market funds, 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 December 31, 2016 , the Company had cash equivalents, consisting of commercial paper, and short-term investments comprised of brokered certificates of deposit, and at December 31, 2015 , the Company had short-term investments and long-term investments comprised of brokered certificates of deposits, 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. At December 31, 2015 , the Company's preferred stock investment in ContraVir Pharmaceuticals was categorized as Level 3 as there were significant unobservable inputs. The valuation of the investment at December 31, 2015 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, which ended on June 17, 2016. An option pricing model was used to determine the discount for lack of marketability of 10% at December 31, 2015 . The key unobservable inputs used in the option pricing model at December 31, 2015 were (i) exercise price - $1.54 , (ii) dividend yield - 0% , (iii) expected holding period - 0.46 years , (iv) risk-free rate - 0.44% , and (v) volatility - 75% . On September 30, 2016, the Company converted its preferred stock investment in ContraVir into 1,071,429 shares of ContraVir common stock, which was categorized as a Level 1 asset and valued based on ContraVir's common stock value. 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 market value. The Company does not currently intend to sell, and is not more likely than not to be required to sell, its investment in ContraVir before recovery of its market value. The change in valuation for the years ended December 31, 2016 and 2015 , primarily based on changes in the fair value of ContraVir common shares, was recorded to unrealized (loss) gain on investments, net 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. 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 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 $ — Fair Value Measurements December 31, 2015 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 19,795 $ 19,795 $ — $ — Total cash equivalents 19,795 19,795 — — Short-term investments Certificates of deposit 23,030 — 23,030 — U.S. Treasury securities 175,214 175,214 — — Preferred stock of U.S. corporation 1,485 — — 1,485 Total short-term investments 199,729 175,214 23,030 1,485 Long-term investments Certificates of deposit 7,668 — 7,668 — U.S. Treasury securities 116,372 116,372 — — Total long-term investments 124,040 116,372 7,668 — Total assets $ 343,564 $ 311,381 $ 30,698 $ 1,485 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 January 1, 2014 $ — Investment acquired 1,545 Fair value increase recorded in other comprehensive loss 236 Fair value at December 31, 2014 1,781 Fair value decrease recorded in other comprehensive loss (296 ) Fair value at December 31, 2015 1,485 Fair value decrease recorded in other comprehensive loss (371 ) Fair value transferred to Level 2 (1,114 ) Fair value at December 31, 2016 $ — Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2016 2015 Prepaid research and development expenses $ 843 $ 4,165 Interest receivable 772 670 Prepaid insurance 389 385 Other prepaid expenses and current assets 841 851 Total prepaid expenses and other current assets $ 2,845 $ 6,071 Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is determined on a straight-line basis over the estimated useful lives of the assets, which generally range from three to five years . Leasehold improvements are amortized over the shorter of the useful life of the asset or the term of the related lease . Maintenance and repairs are charged against expense as incurred. Impairment of Long-Lived Assets The Company evaluates long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If the estimated future cash flows (undiscounted and without interest charges) from the use of an asset are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. To date, no such write-downs have occurred. Deferred Lease Obligations The Company recognizes rent expense on a straight-line basis over the non-cancelable term of its operating lease and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. The Company also records landlord-funded lease incentives, such as reimbursable leasehold improvements, as a deferred rent liability, which is amortized as a reduction of rent expense over the non-cancelable term of its operating lease. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2016 2015 Accrued compensation $ 2,906 $ 2,939 Accrued research and development expenses 2,257 3,596 Other accrued liabilities 1,052 3,186 Total accrued liabilities $ 6,215 $ 9,721 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. 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 and by the Financial Accounting Standards Board. Following these accounting pronouncements, revenue is recognized when all four of the following criteria are met: (i) persuasive evidence of an arrangement exists; (ii) delivery of the products and/or services has occurred and risk of loss has passed; (iii) the selling price is fixed or determinable; and (iv) collectability is reasonably assured. For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively. Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of the Company’s substantive performance obligations. If the Company does not have substantive performance obligations, the Company recognizes non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation. Milestone payments are recognized when earned, provided that (i) the milestone event is substantive; (ii) there is no ongoing performance obligation related to the achievement of the milestone earned; and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement; and the related risk associated with the achievement of the milestone. Contingent based event payments the Company may receive under a license or collaboration agreement will be recognized when received. For the years ended December 31, 2016 , 2015 and 2014 , contract and grant revenue consisted only of revenue from the BARDA contract as there was no grant revenue. The Company recognizes contract and grant revenue as qualifying research activities are conducted based on invoices received from the Company’s vendors. Changes in fringe and indirect rates are recognized as a change in estimate in the period such rate changes are approved by BARDA. For the year ended December 31, 2015, collaboration and licensing revenue primarily consisted of the upfront license fee payment from ContraVir recognized when we completed our performance obligations. 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 December 31, 2016 , 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. Research and Development Expenses Major components of research and development costs include cash compensation, stock based compensation, pre-clinical studies, clinical trial and related clinical manufacturing, drug development, materials and supplies, legal, regulatory compliance, and fees paid to consultants and other entities that conduct certain research and development activities on the Company’s behalf. Research and development costs, including upfront fees and milestones paid to contract research organizations, are expensed as goods as received or services rendered. Costs incurred in connection with clinical trial activities for which the underlying nature of the activities themselves do not directly relate to active research and development, such as costs incurred for market research and focus groups linked to clinical strategy as well as costs to build the Company’s brand, are not included in research and development costs but are reflected as general and administrative costs. Interest Income (Expense), Net Interest income (expense), net primarily includes interest earned on short-term and long-term investments, interest incurred on loans payable, the amortization of deferred financing costs related to fees paid to attorneys and other non-lender entities in order to acquire debt, and the amortization of debt discount related to fees paid to the lender in order to acquire debt. Income Taxes Deferred tax assets and liabilities are determined based on differences between the financial and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are established when the Company determines that it is more likely than not that some portion of a deferred tax asset will not be realized. The Company has incurred operating losses from April 7, 2000 (inception) through December 31, 2016 , and therefore has not recorded any current provision for income taxes. Additionally, the Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefit recognized in the financial statements for a particular tax position is based on the largest benefit that is more likely than not to be realized upon settlement. Accordingly, the Company establishes reserves for uncertain tax positions. Share-Based Compensation The Company measures and recognizes compensation expense for all share-based payment awards made to employees and directors, including employee stock options, restricted stock units and the employee stock purchase plan purchase rights, based on estimated fair values. The fair value of employee stock options and employee stock purchase plan purchase rights is estimated on the grant date using the Black-Scholes valuation model. The grant-date fair value for restricted stock units is based upon the market price of the Company's common stock on the date of the grant. The value of the portion of the award that is ultimately expected to vest is recorded as expense over the requisite service periods. The Company also accounts for equity instruments issued to non-employees using a fair value approach. The Company values equity instruments, stock options and warrants granted to lenders and consultants using the Black-Scholes valuation model. The measurement of non-employee share-based compensation is subject to periodic adjustments as the underlying equity instruments vest and is recognized as an expense over the term of the related financing or the period over which services are received. 401(k) Plan The Company maintains a defined contribution employee retirement plan (“401(k) plan”). Historically, the Company has not made contributions into the 401(k) plan on behalf of participants. In March 2015, the Company began making matching contributions into the 401(k) plan on behalf of participants. For the years ended December 31, 2016 and 2015 , the Company recognized expenses for matching contributions of $0.4 million and $0.3 million , respectively. Basic and Dilutive Net Loss Per Share of Common Stock Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of 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 at December 31, 2016 , 2015 and 2014 . 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 1,012,928 , 1,202,887 and 2,170,660 for the years ended December 31, 2016 , 2015 and 2014 , respectively. Segments The Company operates in only one segment. The chief operating decision-maker, who is the Company’s Chief Executive Officer, and management use cash flows as the primary measure to manage the business and do not segment the business for internal reporting or decision making. Impact of Recently Issued Accounting Standards In 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 made progress toward completing its evaluation of the potential changes from adopting this new standard on its financial reporting and disclosures. The Company expects to complete this process in the second half of 2017. 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 18, 2018. The Company is currently analyzing the impact of the adoption of ASU No. 2016-02 on its consolidated financial statements. 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. The Company is currently analyzing the impact of the adoption of ASU No. 2016-09 on its consolidated financial statements. Impact of Recently Adopted Accounting Standards In June 2015, the FASB issued ASU 2015-10, “Technical Corrections and Improvements.” The amendments in ASU 2015-10 clarify and correct some of the differences 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 a

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments [Abstract]
Investments	Investments The following tables summarize the Company's short-term and long-term investments (in thousands): December 31, 2016 Amortized Cost Gross Unrealized Gross Unrealized Estimated 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 December 31, 2015 Amortized Cost Gross Unrealized Gross Unrealized Estimated Certificates of deposit $ 30,724 $ 2 $ (28 ) $ 30,698 U.S. Treasury securities 292,264 — (678 ) 291,586 Preferred stock of U.S. corporation 1,545 — (60 ) 1,485 Total investments $ 324,533 $ 2 $ (766 ) $ 323,769 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): 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 December 31, 2015 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Certificates of deposit $ 24,450 $ (28 ) $ — $ — $ 24,450 $ (28 ) U.S. Treasury securities 291,586 (678 ) — — 291,586 (678 ) Preferred stock of U.S. corporation 1,485 (60 ) — — 1,485 $ (60 ) Total $ 317,521 $ (766 ) $ — $ — $ 317,521 $ (766 ) Number of securities with unrealized losses 180 — 180 The following table summarizes the scheduled maturity for the Company's investments at December 31, 2016 (in thousands): December 31, 2016 Maturing in one year or less $ 179,272 Maturing after one year through two years 47,407 Total debt investments $ 226,679 Common stock of U.S. corporation 1,286 Total investments $ 227,965

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment, net of accumulated depreciation consisted of the following (in thousands): December 31, 2016 2015 Lab equipment $ 2,419 $ 1,946 Leasehold improvements 1,570 1,463 Computer equipment 1,262 1,063 Office furniture and equipment 586 536 Property and equipment 5,837 5,008 Less accumulated depreciation (2,994 ) (1,963 ) Property and equipment, net of accumulated depreciation $ 2,843 $ 3,045

Loan Payable

Loan Payable	12 Months Ended
	Dec. 31, 2016
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 that was available to be drawn by December 31, 2012 upon meeting one of three stated financial and/or operational goals. The borrowings under the LSA were 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 was paid in full as of December 31, 2015, had an interest-only period of six months followed by a principal and interest amortization period of 32 months with interest being charged at 8.25% . There were certain fees in accordance with the LSA which were recorded as discounts or short-term liabilities depending on the nature of the fees and accreted through interest expense over the life of the loans. As of December 31, 2015, the LSA was paid in full and no amounts remain outstanding.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
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. The Company has the following minimum rental payments under non-cancelable operating lease obligations that existed at December 31, 2016 (in thousands): Years Ending December 31, Minimum Rental Payment 2017 $ 825 2018 759 2019 665 2020 672 2021 112 Total future minimum rental payments $ 3,033 Rent expense under non-cancelable operating leases and other month-to-month equipment rental agreements, including common area maintenance fees, totaled approximately $0.7 million , $0.6 million , and $0.4 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. Sublease The Company subleases 3,537 square feet of its office space under non-cancelable operating lease that expires February 2021. Total future minimum rentals under the non-cancelable operating sublease as of December 31, 2016 are presented below (in thousands): Years Ending December 31, Minimum Sublease Rentals 2017 $ 60 2018 74 2019 77 2020 81 2021 14 Total future minimum sublease rentals $ 306 Significance of Revenue Source The Company is the recipient of federal research contract funds from BARDA. Periodic audits are required under the grant and contract agreements and certain costs may be questioned as appropriate under the agreements. Management believes that such amounts in the current year, if any, are not significant. Accordingly, no provision for refundable amounts under the agreements has been made as of December 31, 2016 and 2015 .

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Stockholders' Equity (Deficit)	Stockholders’ Equity (Deficit) Common Stock The Company’s common stock consists of 200 million authorized shares at December 31, 2016 and 2015 , and 46.5 million and 46.2 million shares issued and outstanding at December 31, 2016 and December 31, 2015 , respectively. On May 27, 2014, the Company completed an underwritten public offering of 8,395,000 shares of common stock, including 1,095,000 shares sold pursuant to the full exercise of an over-allotment option previously granted to the underwriters. All of the shares were offered by the Company at a price to the public of $14.22 per share. Net proceeds to the Company from this offering, after deducting underwriting discounts and commissions and other offering expenses payable by the Company, were approximately $111.8 million . On November 5, 2014, the Company completed an underwritten public offering of 4,197,500 shares of common stock, including 547,500 shares sold pursuant to the full exercise of an option previously 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 $29.00 per share. The net proceeds from this offering, after deducting underwriting discounts and commissions and other offering expenses payable by us, were approximately $114.0 million . 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 . Shares Reserved for Future Issuance The Company has reserved shares of common stock for future issuances as follows: December 31, 2016 2015 For exercise of common stock warrants 227,794 227,794 For exercise of outstanding common stock options 4,342,466 2,746,395 For delivery upon vesting of outstanding restricted stock units 946,200 — For future equity awards under the 2013 Equity Incentive Plan 662,180 1,609,791 For future purchases under the 2013 Employee Stock Purchase Plan 1,612,759 1,298,333 Total shares of common stock reserved for future issuances 7,791,399 5,882,313 Stock Options In connection with the Company’s IPO, the Company adopted the 2013 Equity Incentive Plan (the 2013 Plan). The 2013 Plan provides for the grant of incentive stock options (ISOs), nonstatutory stock options (NSOs), stock appreciation rights, restricted stock awards, restricted stock unit (RSU) awards, performance-based stock awards, and other forms of equity compensation (collectively, stock awards), all of which may be granted to employees, including officers, non-employee directors and consultants of the Company and its affiliates. Additionally, the 2013 Plan provides for the grant of performance cash awards. ISOs may be granted only to employees. All other awards may be granted to employees, including officers, and to non-employee directors and consultants. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (i) 1,408,450 shares, plus (ii) 244,717 shares, which was the number of shares reserved for issuance under the Company’s 2012 Equity Incentive Plan (the 2012 Plan) at the time the 2013 Plan became effective, plus (iii) any shares subject to outstanding stock options or other stock awards that would have otherwise returned to the 2012 Plan (such as upon the expiration or termination of a stock award prior to vesting). Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2014 and continuing through and including January 1, 2023, by 2.5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. The maximum number of shares that may be issued upon the exercise of ISOs under the 2013 Plan is 2,816,901 shares. Following the effectiveness of the 2013 Plan in April 2013, no further grants were made under the 2012 Plan. At the Company's annual meeting held on June 20, 2014, shareholders approved a change to the annual automatic increase in the number of common shares to be reserved for issuance under the 2013 Plan by changing the percentage increase to 4.0% , or a lesser number of shares determined by the Company's board of directors. The Company estimates the fair value of its share-based awards to employees, directors and consultants using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of highly complex and subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the Company’s limited operating history and historical and implied volatility data, the Company has based its estimates of expected volatility on a blend of Company specific historical data and a group of similar public traded companies. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, positions within the industry, and with historical share price information sufficient to meet the expected life of its stock options. For employee stock options the Company uses historical exercise data to estimate the expected life. The expected term for share-based compensation granted to non-employees is the contractual life. The risk-free interest rates for the periods within the expected life of the option are based on the U.S. Treasury instrument with a life that is similar to the expected life of the option grant. The Company has never paid, and does not expect to pay, dividends in the foreseeable future. The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the stock options granted: Years Ended December 31, 2016 2015 2014 Expected volatility 85.16 % 66.89 % 71.47 % Expected term (in years) 6.0 6.0 6.0 Weighted-average risk-free interest rate 1.70 % 1.53 % 1.91 % Expected dividend yield — % — % — % Weighted-average fair value per option $ 5.62 $ 25.18 $ 14.01 The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting option forfeitures and record share-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised. For the years ended December 31, 2016 , 2015 and 2014 , the Company applied a forfeiture rate based on the Company’s historical forfeitures. A summary of activity related to the Company’s stock options is as follows: Number of Options Weighted-Average Weighted-Average Total Intrinsic Value Balance, January 1, 2015 1,859,970 $ 15.79 8.46 Granted 1,249,683 41.80 — Exercised (292,581 ) 7.22 — Forfeited (70,677 ) 30.78 — Balance, December 31, 2015 2,746,395 $ 28.19 8.41 Granted 2,418,551 7.76 — Exercised (48,441 ) 3.48 — Forfeited (774,039 ) 24.13 — Balance, December 31, 2016 4,342,466 $ 17.81 8.09 $ 540,234 Exercisable at December 31, 2016 2,033,315 $ 19.77 7.44 $ 483,421 Vested or expected to vest at December 31, 2016 4,275,950 $ 17.83 8.08 $ 537,904 As of December 31, 2016 , there was approximately $22.8 million of total unrecognized compensation cost related to non-vested share-based compensation arrangements granted under the 2013 Plan. That compensation cost is expected to be recognized over a weighted-average period of approximately 2.28 years . Other information regarding the Company’s stock options is as follows (in thousands, except per share data): Years Ended December 31, 2016 2015 2014 Weighted-average grant-date fair value per share of options granted $ 5.62 $ 25.18 $ 14.01 Total intrinsic value of options exercised $ 119 $ 10,139 $ 30,438 Total fair value of shares vested $ 13,330 $ 11,498 $ 4,696 The following table summarizes, at December 31, 2016 , by price range: (1) for stock option awards outstanding under the 2013 Plan, the number of stock option awards outstanding, their weighted-average remaining life and their weighted-average exercise price; and (2) for stock option awards exercisable under the Plan, the number of stock option awards exercisable and their weighted-average exercise price: Outstanding Exercisable Range Number Weighted-Average Remaining Contractual Life (in years) Weighted-Average Exercise Price Number Weighted-Average Exercise Price $1.53 to 7.57 504,307 5.85 $ 4.00 399,862 $ 3.89 7.58 to 8.06 1,927,576 9.02 8.06 456,715 8.06 15.79 to 18.75 423,521 7.05 17.83 313,439 17.84 18.76 to 39.17 599,121 7.56 25.43 398,537 25.04 39.18 to 53.74 887,941 8.21 41.67 464,762 41.71 $1.53 to 53.74 4,342,466 8.09 $ 17.81 2,033,315 $ 19.77 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. The purpose of the ESPP is to retain the services of new employees and secure the services of new and existing employees while providing incentives for such individuals to exert maximum efforts toward the Company’s success and that of its affiliates. The ESPP initially authorized the issuance of 704,225 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of its designated affiliates. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2014 through January 1, 2023 by the least of (a) 1% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (b) 422,535 shares, or (c) a number determined by the Company’s board of directors that is less than (a) and (b). The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code of 1986. On January 1, 2015 and 2016, the common stock reserved for future issuance under the ESPP was automatically increased by an additional 410,317 and 422,535 shares, respectively, bringing the total number of shares of common stock that may be purchased under the ESPP to 1,381,191 and 1,803,726 , respectively. The Company has reserved a total of 1,803,726 shares of common stock to be purchased under the ESPP, of which 1,612,759 and 1,298,333 shares remained available for purchase at December 31, 2016 and 2015 , respectively. 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 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 issued 108,109 and 56,583 shares of common stock pursuant to the ESPP for the year ended December 31, 2016 and 2015 , respectively. Compensation expense for purchase rights under the ESPP related to the purchase discount and the “look-back” option were determined using a Black-Scholes option pricing model. The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the ESPP purchase rights: Years Ended December 31, 2016 2015 2014 Expected volatility 111.57 % 57.77 % 74.24 % Expected term (in years) 1.37 1.15 0.8 Weighted-average risk-free interest rate 0.75 % 0.43 % 0.09 % Expected dividend yield — % — % — % Weighted-average option value per share $ 3.20 $ 22.10 $ 9.93 As of December 31, 2016 , the Company had a liability of $0.3 million representing employees' contributions to the ESPP. Restricted Stock Units In 2016, the Company issued Restricted Stock Units (RSUs) to certain employees which vest over a service period of 3 years and 1.5 years for executives and non-executives, respectively. When vested, the RSU represented the right to be issued the number of shares of the Company’s common stock that is equal to the number of RSUs granted. A summary of activity related to the Company’s RSUs is as follows: Number of Restricted Weighted-Average Grant-Date Fair Value Balance, January 1, 2016 — Granted 1,209,000 $ 4.91 Share issuance (203,400 ) 4.91 Forfeited (59,400 ) 4.91 Balance, December 31, 2016 946,200 $ 4.91 Warrants In February 2011, the Company issued warrants to purchase an aggregate of 5,501,215 shares of Series F redeemable convertible preferred stock at an exercise price of $2.045 per share. Upon the completion of the Company’s IPO in April 2013, these warrants were converted into warrants to purchase 1,549,628 shares of common stock at an exercise price of $7.26 per share. The warrants are exercisable at any time and expire on February 4, 2018. At December 31, 2016 and 2015 , warrants for the purchase of 227,794 shares of common stock were issued, outstanding and exercisable . Stock-based Compensation 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 years ended December 31, 2016 , 2015 , and 2014 , there was no non-employee share-based compensation expense. Total stock-based compensation expense was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Income Statement Classification: Research and development expense $ 7,137 $ 5,578 $ 1,085 General and administrative expense 9,086 7,381 3,326 Total stock-based compensation expense $ 16,223 $ 12,959 $ 4,411 Cash received from exercises under all share-based payment arrangements for 2016 , 2015 and 2014 was $0.6 million , $3.2 million and $5.0 million , respectively. There was no actual tax benefit realized for the tax deductions from exercises of the share-based payment arrangements during 2016 , 2015 or 2014 . The Company continues to account for stock options issued to non-employees using a fair value approach. The compensation costs of these arrangements are subject to re-measurement over the vesting terms as earned. Compensation cost for performance-based awards is recognized when it is probable that the performance criteria will be met.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes No income tax expense or benefit has been recorded for the years ended December 31, 2016 , 2015 or 2014 . This is due to the establishment of a valuation allowance against the deferred tax assets generated during those periods. At December 31, 2016 , the Company has concluded that it is more likely than not that the Company may not realize the benefit of its deferred tax assets due to its history of losses. Accordingly, the net deferred tax assets have been fully reserved. A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2016 , 2015 , and 2014 (in thousands, except percentages): 2016 2015 2014 Amount % of Pretax Amount % of Pretax Amount % of Pretax Income tax benefit at statutory rate $ (25,973 ) 34.0 % $ (39,907 ) 34.0 % $ (20,166 ) 34.0 % State income taxes (1,544 ) 2.0 % (2,176 ) 1.9 % (1,343 ) 2.3 % Research and development credits (2,691 ) 3.5 % (5,698 ) 4.9 % (2,577 ) 4.3 % Foreign rate differential (2 ) — % 2 — % — — % Permanent items 2,537 (3.3 )% 3,687 (3.1 )% 1,525 (2.6 )% Provision to return adjustments 259 (0.3 )% (426 ) 0.2 % 64 (0.1 )% Effect of change in state tax rate 1,585 (2.1 )% 932 (0.8 )% 2 — % Increase in unrecognized tax benefits 444 (0.6 )% 950 (0.8 )% 425 (0.7 )% Change in valuation allowance 25,385 (33.2 )% 42,636 (36.3 )% 22,070 (37.2 )% Net benefit $ — — % $ — — % $ — — % The components of deferred tax assets and liabilities at December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Domestic net operating loss carryforwards $ 114,111 $ 93,923 Foreign net operating loss carryforwards — 2 Research and development expenses 813 1,289 Capitalized Section 174 expenses 48 51 Research and development credits 10,907 8,889 Accrued bonuses 1,006 822 Share-based compensation 7,214 3,671 Other 460 604 Total gross deferred tax assets 134,559 109,251 Valuation allowance (134,496 ) (109,111 ) Total deferred tax assets 63 140 Deferred tax liabilities: Other (63 ) (140 ) Total deferred tax liabilities (63 ) (140 ) Total deferred tax assets and liabilities, net $ — $ — At December 31, 2016 , the Company had net operating loss carryforwards for federal and state tax purposes of approximately $356.1 million and $287.2 million respectively. At December 31, 2015 , the Company had net operating loss carryforwards for federal and state tax purposes of approximately $296.6 million and $233.9 million respectively. The federal losses begin to expire in 2020 and the state losses begin to expire in 2018 . The Company’s federal and state net operating loss carryforwards include approximately $35.9 million of excess tax benefits related to deductions from the exercise of stock options. The tax benefit of these deductions has not been recognized in deferred tax assets. If utilized, the benefits from these deductions will be recorded as adjustments to additional paid-in capital. In addition, the Company has tax credit carryforwards for federal tax purposes of approximately $14.5 million as of December 31, 2016 , which begin to expire in 2022 . The future utilization of net operating loss and tax credit carryforwards may be limited due to changes in ownership. Management has recorded a valuation allowance for all of the deferred tax assets due to the uncertainty of future taxable income. The Company incorporated a subsidiary in the United Kingdom in 2014. However, the subsidiary has had minimal activity since inception. The subsidiary recorded a small amount of net income as of December 31, 2016 and a small net loss as of December 31, 2015 and as such, has no undistributed earnings. In general, if the Company experiences a greater than 50% aggregate change in ownership of certain significant stockholders over a three-year period (a Section 382 ownership change), utilization of its pre-change net operating loss carryforwards is subject to an annual limitation under Section 382 of the Internal Revenue Code (and similar state laws). The annual limitation generally is determined by multiplying the value of the Company’s stock at the time of such ownership change (subject to certain adjustments) by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the net operating loss carryforwards before utilization and may be substantial. The ability of the Company to use its net operating loss carryforwards may be limited or lost if the Company experiences a Section 382 ownership change in connection with offerings or as a result of future changes in its stock ownership. Losses from a specific period may be subject to multiple limitations, and would generally be limited by the lowest of those limitations. The Company has determined that a Section 382 ownership change occurred in 2002, and as such, losses incurred prior to that date are subject to an annual limitation of at least $64,000 . Additionally, the Company has determined that a Section 382 ownership change occurred in 2007, and as such, losses incurred prior to that date are subject to an annual limitation of at least $762,000 . The Company evaluated Section 382 ownership changes subsequent to 2007 through September 30, 2015 and concluded that a Section 382 ownership change occurred in 2013 as a result of the initial public offering. As such, losses incurred prior to that date are subject to an annual limitation of at least $6.7 million . As of December 31, 2016 and 2015 , the total unrecognized tax benefits were approximately $2.4 million and $2.0 million , respectively, and of this total, none would reduce the Company’s effective tax rate if recognized. The Company does not anticipate a significant change in total unrecognized tax benefits or the Company’s effective tax rate due to the settlement of audits or the expiration of statutes of limitations within the next twelve months. Furthermore, the Company does not expect any cash settlement with the taxing authorities as a result of these unrecognized tax benefits as the Company has sufficient unutilized carryforward attributes to offset the tax impact of these adjustments. The Company has determined that there may be a future limitation on the Company’s ability to utilize its entire federal R&D credit carryover. Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the years ended December 31, 2016 and 2015 , as follows (in thousands): Balance at December 31, 2014 $ 1,006 Increases related to 2015 940 Increases related to prior periods 10 Balance at December 31, 2015 1,956 Increases related to 2016 444 Increases related to prior periods — Balance at December 31, 2016 $ 2,400 The Company has determined that it had no other material uncertain tax benefits for the year ended December 31, 2016 . As of January 1, 2017, due to the carry forward of unutilized net operating losses and research and development credits, the Company is subject to U.S. Federal and state income tax examinations for the tax years 2000 through 2016 . The Company recognizes accrued interest related to unrecognized tax benefits in interest expense and penalties in operating expense. No amounts were accrued for the payment of interest and penalties at December 31, 2016 .

Significant Agreements

Significant Agreements	12 Months Ended
	Dec. 31, 2016
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. As partial consideration for the rights granted to the Company under the license agreement, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights. In connection with the development and commercialization of brincidofovir and CMX157, the Company could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement. Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UC Patent Rights for all human and veterinary uses, and to sublicense such rights. UC retained the right, on behalf of itself and other non-profit institutions, to use the UC Patent Rights for educational and research purposes and to publish information about the UC Patent Rights. In consideration for the rights granted under the license agreement, the Company has issued UC an aggregate of 64,788 shares of common stock. As additional consideration, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights, plus certain annual fees to maintain such patents until the Company commercializes a product utilizing UC Patent Rights. In 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 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. As a result of meeting certain milestones and sublicense fees related to this license agreement, the Company recognized expenses of $0.06 million for the year ended December 31, 2014. 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 option segment is expected to end on June 30, 2017 and the third option segment is scheduled to end on March 31, 2017. As of December 31, 2016 , the Company has recognized revenue in aggregate of $51.7 million with respect to the base performance segment and the first three extension periods. 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 ( 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. The Company recorded this amount as a long-term investment and deferred revenue, which is 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 December 31, 2016 and 2015 , the fair value of the investment was recorded as a short-term investment of $1.3 million and $1.5 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.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2016 and 2015 are as follows (in thousands, except share and per share data): 2016 Quarters Fourth Third Second First Total revenues $ 1,980 $ 653 $ 1,841 $ 1,228 Operating loss (15,373 ) (17,422 ) (18,525 ) (26,632 ) Net loss (14,957 ) (17,025 ) (18,148 ) (26,260 ) Net loss per share, basic and diluted $ (0.32 ) $ (0.37 ) $ (0.39 ) $ (0.57 ) Weighted-average shares outstanding, basic and diluted 46,431,809 46,236,749 46,214,086 46,184,134 2015 Quarters Fourth Third Second First Total revenues $ 3,110 $ 2,271 $ 4,143 $ 1,238 Operating loss (38,223 ) (32,748 ) (24,951 ) (22,329 ) Net loss (37,842 ) (32,449 ) (24,815 ) (22,266 ) Net loss per share, basic and diluted $ (0.82 ) $ (0.70 ) $ (0.59 ) $ (0.54 ) Weighted-average shares outstanding, basic and diluted 46,151,384 46,059,112 42,079,716 41,220,989 Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share calculations will not necessarily equal the annual per share calculation. Diluted weighted-average shares outstanding are identical to basic weighted-average shares outstanding and diluted net loss per share is identical to basic net loss per share for all quarters of 2016 and 2015 .

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
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 December 31, 2016 , and events which occurred subsequently but were not recognized in the financial statements.

The Business and Summary of S18

The Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company, and its wholly owned subsidiaries. The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The preparation of the Company’s consolidated financial statements requires estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the consolidated financial statements and accompanying notes. Although these estimates are based on knowledge of current events and actions the Company may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
Reclassifications	Reclassifications Certain prior period amounts in the accompanying consolidated financial statements have been reclassified to conform to the current year presentation. These reclassifications had no effect on previously reported net income or stockholders' equity (deficit).
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market funds and commercial paper.
Investments	Investments Investments consist primarily of brokered certificates of deposit, U.S. Treasury securities and stock of a U.S. corporation. The Company invests in high-credit quality investments in accordance with its investment policy which minimizes the probability of loss. Available-for-sale securities are carried at fair value as determined by quoted market prices, with the unrealized gains and losses, net of tax, reported as a separate component of stockholders equity. Realized gains and losses are determined using the specific identification method and transactions are recorded on a settlement date basis in interest income or expense, net. Investments with original maturities beyond three months at the date of purchase and which mature on, or less than twelve months from, the balance sheet date are classified as short-term. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term. The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. 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 amortized cost basis. The Company does not intend to sell, and is not likely to be required to sell, the available-for-sale securities in an unrealized loss position before recovery of the amortized cost bases of the securities, which may be maturity. Any such declines in value judged to be other-than-temporary on available-for-sale securities are reported in interest income or expense, net. There were no such declines in value for the years ended December 31, 2016 , 2015 and 2014 . The Company recognizes interest income on an accrual basis in interest income (expense), net in the Consolidated Statements of Operations and Comprehensive Loss.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, short-term investments, long-term investments and accounts receivable. The Company is exposed to credit risk, subject to federal deposit insurance, in the event of default by the financial institutions holding its cash and cash equivalents to the extent of amounts recorded on the balance sheets. Accounts receivable represent amounts due from an agency of the federal government.
Accounts Receivable	Accounts Receivable Accounts receivable at December 31, 2016 and December 31, 2015 consisted of amounts billed under the Company’s contract with the Biomedical Advanced Research and Development Authority (BARDA). Receivables under the BARDA contract are recorded as qualifying research activities are conducted and invoices from the Company’s vendors are received. The Company carries its accounts receivable at cost less an allowance for doubtful accounts. On a periodic basis, the Company evaluates its accounts receivable and establishes an allowance based on its history of collections and write-offs and the current status of all receivables. The Company does not accrue interest on trade receivables. If accounts become uncollectible, they will be written off through a charge to the allowance for doubtful accounts. The Company has not recorded a charge to allowance for doubtful accounts as management believes all receivables are fully collectible.
Fair Value of Financial Instruments	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. There were no transfers between Level 1 and Level 2 or transfers to or from Level 3 during the year ended December 31, 2015 . When the 18 month restriction on selling the Company's investment in ContraVir Pharmaceuticals ended on June 17, 2016, the investment was transferred from Level 3 to Level 2 as the fair value was based on quoted prices for similar assets and there were no significant unobservable inputs. The Company's investment in ContraVir Pharmaceuticals transferred from Level 2 to Level 1 when the Company converted its investment in Series B Preferred shares into common stock in 2016. At December 31, 2016 and 2015 , the Company had cash equivalents, consisting of money market funds, 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 December 31, 2016 , the Company had cash equivalents, consisting of commercial paper, and short-term investments comprised of brokered certificates of deposit, and at December 31, 2015 , the Company had short-term investments and long-term investments comprised of brokered certificates of deposits, 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. At December 31, 2015 , the Company's preferred stock investment in ContraVir Pharmaceuticals was categorized as Level 3 as there were significant unobservable inputs. The valuation of the investment at December 31, 2015 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, which ended on June 17, 2016. An option pricing model was used to determine the discount for lack of marketability of 10% at December 31, 2015 . The key unobservable inputs used in the option pricing model at December 31, 2015 were (i) exercise price - $1.54 , (ii) dividend yield - 0% , (iii) expected holding period - 0.46 years , (iv) risk-free rate - 0.44% , and (v) volatility - 75% . On September 30, 2016, the Company converted its preferred stock investment in ContraVir into 1,071,429 shares of ContraVir common stock, which was categorized as a Level 1 asset and valued based on ContraVir's common stock value. 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 market value. The Company does not currently intend to sell, and is not more likely than not to be required to sell, its investment in ContraVir before recovery of its market value. The change in valuation for the years ended December 31, 2016 and 2015 , primarily based on changes in the fair value of ContraVir common shares, was recorded to unrealized (loss) gain on investments, net 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.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is determined on a straight-line basis over the estimated useful lives of the assets, which generally range from three to five years . Leasehold improvements are amortized over the shorter of the useful life of the asset or the term of the related lease . Maintenance and repairs are charged against expense as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If the estimated future cash flows (undiscounted and without interest charges) from the use of an asset are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. To date, no such write-downs have occurred.
Deferred Lease Obligation	Deferred Lease Obligations The Company recognizes rent expense on a straight-line basis over the non-cancelable term of its operating lease and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. The Company also records landlord-funded lease incentives, such as reimbursable leasehold improvements, as a deferred rent liability, which is amortized as a reduction of rent expense over the non-cancelable term of its operating lease.
Revenue Recognition	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. 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 and by the Financial Accounting Standards Board. Following these accounting pronouncements, revenue is recognized when all four of the following criteria are met: (i) persuasive evidence of an arrangement exists; (ii) delivery of the products and/or services has occurred and risk of loss has passed; (iii) the selling price is fixed or determinable; and (iv) collectability is reasonably assured. For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively. Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of the Company’s substantive performance obligations. If the Company does not have substantive performance obligations, the Company recognizes non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation. Milestone payments are recognized when earned, provided that (i) the milestone event is substantive; (ii) there is no ongoing performance obligation related to the achievement of the milestone earned; and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement; and the related risk associated with the achievement of the milestone. Contingent based event payments the Company may receive under a license or collaboration agreement will be recognized when received. For the years ended December 31, 2016 , 2015 and 2014 , contract and grant revenue consisted only of revenue from the BARDA contract as there was no grant revenue. The Company recognizes contract and grant revenue as qualifying research activities are conducted based on invoices received from the Company’s vendors. Changes in fringe and indirect rates are recognized as a change in estimate in the period such rate changes are approved by BARDA. For the year ended December 31, 2015, collaboration and licensing revenue primarily consisted of the upfront license fee payment from ContraVir recognized when we completed our performance obligations.
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 December 31, 2016 , 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.
Research and Development Expenses	Research and Development Expenses Major components of research and development costs include cash compensation, stock based compensation, pre-clinical studies, clinical trial and related clinical manufacturing, drug development, materials and supplies, legal, regulatory compliance, and fees paid to consultants and other entities that conduct certain research and development activities on the Company’s behalf. Research and development costs, including upfront fees and milestones paid to contract research organizations, are expensed as goods as received or services rendered. Costs incurred in connection with clinical trial activities for which the underlying nature of the activities themselves do not directly relate to active research and development, such as costs incurred for market research and focus groups linked to clinical strategy as well as costs to build the Company’s brand, are not included in research and development costs but are reflected as general and administrative costs.
Interest Income (Expense), Net	Interest Income (Expense), Net Interest income (expense), net primarily includes interest earned on short-term and long-term investments, interest incurred on loans payable, the amortization of deferred financing costs related to fees paid to attorneys and other non-lender entities in order to acquire debt, and the amortization of debt discount related to fees paid to the lender in order to acquire debt.
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based on differences between the financial and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are established when the Company determines that it is more likely than not that some portion of a deferred tax asset will not be realized. The Company has incurred operating losses from April 7, 2000 (inception) through December 31, 2016 , and therefore has not recorded any current provision for income taxes. Additionally, the Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefit recognized in the financial statements for a particular tax position is based on the largest benefit that is more likely than not to be realized upon settlement. Accordingly, the Company establishes reserves for uncertain tax positions.
Share-Based Compensation	Share-Based Compensation The Company measures and recognizes compensation expense for all share-based payment awards made to employees and directors, including employee stock options, restricted stock units and the employee stock purchase plan purchase rights, based on estimated fair values. The fair value of employee stock options and employee stock purchase plan purchase rights is estimated on the grant date using the Black-Scholes valuation model. The grant-date fair value for restricted stock units is based upon the market price of the Company's common stock on the date of the grant. The value of the portion of the award that is ultimately expected to vest is recorded as expense over the requisite service periods. The Company also accounts for equity instruments issued to non-employees using a fair value approach. The Company values equity instruments, stock options and warrants granted to lenders and consultants using the Black-Scholes valuation model. The measurement of non-employee share-based compensation is subject to periodic adjustments as the underlying equity instruments vest and is recognized as an expense over the term of the related financing or the period over which services are received.
401(k) Plan	401(k) Plan The Company maintains a defined contribution employee retirement plan (“401(k) plan”). Historically, the Company has not made contributions into the 401(k) plan on behalf of participants. In March 2015, the Company began making matching contributions into the 401(k) plan on behalf of participants. For the years ended December 31, 2016 and 2015 , the Company recognized expenses for matching contributions of $0.4 million and $0.3 million , respectively.
Basic and Dilutive Net Loss Per Share of Common Stock	Basic and Dilutive Net Loss Per Share of Common Stock Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of 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 at December 31, 2016 , 2015 and 2014 . 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.
Segments	Segments The Company operates in only one segment. The chief operating decision-maker, who is the Company’s Chief Executive Officer, and management use cash flows as the primary measure to manage the business and do not segment the business for internal reporting or decision making.
Impact of Recently Issued Accounting Standards 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 made progress toward completing its evaluation of the potential changes from adopting this new standard on its financial reporting and disclosures. The Company expects to complete this process in the second half of 2017. 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 18, 2018. The Company is currently analyzing the impact of the adoption of ASU No. 2016-02 on its consolidated financial statements. 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. The Company is currently analyzing the impact of the adoption of ASU No. 2016-09 on its consolidated financial statements. Impact of Recently Adopted Accounting Standards In June 2015, the FASB issued ASU 2015-10, “Technical Corrections and Improvements.” The amendments in ASU 2015-10 clarify and correct some of the differences 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. ASU 2015-10 became effective for the Company beginning in the first quarter of 2016. The Company's adoption of ASU 2015-10 did not have a material impact on its consolidated financial statements.

The Business and Summary of S19

The Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Assets and Liabilities 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 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 $ — Fair Value Measurements December 31, 2015 Total Quoted Prices in Significant Other Significant Cash equivalents Money market funds $ 19,795 $ 19,795 $ — $ — Total cash equivalents 19,795 19,795 — — Short-term investments Certificates of deposit 23,030 — 23,030 — U.S. Treasury securities 175,214 175,214 — — Preferred stock of U.S. corporation 1,485 — — 1,485 Total short-term investments 199,729 175,214 23,030 1,485 Long-term investments Certificates of deposit 7,668 — 7,668 — U.S. Treasury securities 116,372 116,372 — — Total long-term investments 124,040 116,372 7,668 — Total assets $ 343,564 $ 311,381 $ 30,698 $ 1,485
Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis	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 January 1, 2014 $ — Investment acquired 1,545 Fair value increase recorded in other comprehensive loss 236 Fair value at December 31, 2014 1,781 Fair value decrease recorded in other comprehensive loss (296 ) Fair value at December 31, 2015 1,485 Fair value decrease recorded in other comprehensive loss (371 ) Fair value transferred to Level 2 (1,114 ) Fair value at December 31, 2016 $ —
Schedule of Prepaid and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2016 2015 Prepaid research and development expenses $ 843 $ 4,165 Interest receivable 772 670 Prepaid insurance 389 385 Other prepaid expenses and current assets 841 851 Total prepaid expenses and other current assets $ 2,845 $ 6,071
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2016 2015 Accrued compensation $ 2,906 $ 2,939 Accrued research and development expenses 2,257 3,596 Other accrued liabilities 1,052 3,186 Total accrued liabilities $ 6,215 $ 9,721

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments [Abstract]
Summary of Short-term and Long-term Investments	The following tables summarize the Company's short-term and long-term investments (in thousands): December 31, 2016 Amortized Cost Gross Unrealized Gross Unrealized Estimated 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 December 31, 2015 Amortized Cost Gross Unrealized Gross Unrealized Estimated Certificates of deposit $ 30,724 $ 2 $ (28 ) $ 30,698 U.S. Treasury securities 292,264 — (678 ) 291,586 Preferred stock of U.S. corporation 1,545 — (60 ) 1,485 Total investments $ 324,533 $ 2 $ (766 ) $ 323,769
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): 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 December 31, 2015 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Certificates of deposit $ 24,450 $ (28 ) $ — $ — $ 24,450 $ (28 ) U.S. Treasury securities 291,586 (678 ) — — 291,586 (678 ) Preferred stock of U.S. corporation 1,485 (60 ) — — 1,485 $ (60 ) Total $ 317,521 $ (766 ) $ — $ — $ 317,521 $ (766 ) Number of securities with unrealized losses 180 — 180
Summary of the scheduled maturity of Company investments	The following table summarizes the scheduled maturity for the Company's investments at December 31, 2016 (in thousands): December 31, 2016 Maturing in one year or less $ 179,272 Maturing after one year through two years 47,407 Total debt investments $ 226,679 Common stock of U.S. corporation 1,286 Total investments $ 227,965

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment, net	Property and equipment, net of accumulated depreciation consisted of the following (in thousands): December 31, 2016 2015 Lab equipment $ 2,419 $ 1,946 Leasehold improvements 1,570 1,463 Computer equipment 1,262 1,063 Office furniture and equipment 586 536 Property and equipment 5,837 5,008 Less accumulated depreciation (2,994 ) (1,963 ) Property and equipment, net of accumulated depreciation $ 2,843 $ 3,045

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Total future minimum rentals under the non-cancelable operating sublease as of December 31, 2016 are presented below (in thousands): Years Ending December 31, Minimum Sublease Rentals 2017 $ 60 2018 74 2019 77 2020 81 2021 14 Total future minimum sublease rentals $ 306 The Company has the following minimum rental payments under non-cancelable operating lease obligations that existed at December 31, 2016 (in thousands): Years Ending December 31, Minimum Rental Payment 2017 $ 825 2018 759 2019 665 2020 672 2021 112 Total future minimum rental payments $ 3,033

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Schedule of Shares Reserved for Future Issuance	The Company has reserved shares of common stock for future issuances as follows: December 31, 2016 2015 For exercise of common stock warrants 227,794 227,794 For exercise of outstanding common stock options 4,342,466 2,746,395 For delivery upon vesting of outstanding restricted stock units 946,200 — For future equity awards under the 2013 Equity Incentive Plan 662,180 1,609,791 For future purchases under the 2013 Employee Stock Purchase Plan 1,612,759 1,298,333 Total shares of common stock reserved for future issuances 7,791,399 5,882,313
Schedule of Fair Value Assumptions, Stock Options	The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the stock options granted: Years Ended December 31, 2016 2015 2014 Expected volatility 85.16 % 66.89 % 71.47 % Expected term (in years) 6.0 6.0 6.0 Weighted-average risk-free interest rate 1.70 % 1.53 % 1.91 % Expected dividend yield — % — % — % Weighted-average fair value per option $ 5.62 $ 25.18 $ 14.01
Summary of Activity Related to Stock Options	A summary of activity related to the Company’s stock options is as follows: Number of Options Weighted-Average Weighted-Average Total Intrinsic Value Balance, January 1, 2015 1,859,970 $ 15.79 8.46 Granted 1,249,683 41.80 — Exercised (292,581 ) 7.22 — Forfeited (70,677 ) 30.78 — Balance, December 31, 2015 2,746,395 $ 28.19 8.41 Granted 2,418,551 7.76 — Exercised (48,441 ) 3.48 — Forfeited (774,039 ) 24.13 — Balance, December 31, 2016 4,342,466 $ 17.81 8.09 $ 540,234 Exercisable at December 31, 2016 2,033,315 $ 19.77 7.44 $ 483,421 Vested or expected to vest at December 31, 2016 4,275,950 $ 17.83 8.08 $ 537,904
Schedule of Other Information Regarding Stock Options	Other information regarding the Company’s stock options is as follows (in thousands, except per share data): Years Ended December 31, 2016 2015 2014 Weighted-average grant-date fair value per share of options granted $ 5.62 $ 25.18 $ 14.01 Total intrinsic value of options exercised $ 119 $ 10,139 $ 30,438 Total fair value of shares vested $ 13,330 $ 11,498 $ 4,696
Schedule of Share-based Compensation, Shares Authorized	The following table summarizes, at December 31, 2016 , by price range: (1) for stock option awards outstanding under the 2013 Plan, the number of stock option awards outstanding, their weighted-average remaining life and their weighted-average exercise price; and (2) for stock option awards exercisable under the Plan, the number of stock option awards exercisable and their weighted-average exercise price: Outstanding Exercisable Range Number Weighted-Average Remaining Contractual Life (in years) Weighted-Average Exercise Price Number Weighted-Average Exercise Price $1.53 to 7.57 504,307 5.85 $ 4.00 399,862 $ 3.89 7.58 to 8.06 1,927,576 9.02 8.06 456,715 8.06 15.79 to 18.75 423,521 7.05 17.83 313,439 17.84 18.76 to 39.17 599,121 7.56 25.43 398,537 25.04 39.18 to 53.74 887,941 8.21 41.67 464,762 41.71 $1.53 to 53.74 4,342,466 8.09 $ 17.81 2,033,315 $ 19.77
Schedule of Fair Value Assumptions, Employee Stock Purchase Plan	The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the ESPP purchase rights: Years Ended December 31, 2016 2015 2014 Expected volatility 111.57 % 57.77 % 74.24 % Expected term (in years) 1.37 1.15 0.8 Weighted-average risk-free interest rate 0.75 % 0.43 % 0.09 % Expected dividend yield — % — % — % Weighted-average option value per share $ 3.20 $ 22.10 $ 9.93
Summary of Activity Related to Restricted Stock Units	A summary of activity related to the Company’s RSUs is as follows: Number of Restricted Weighted-Average Grant-Date Fair Value Balance, January 1, 2016 — Granted 1,209,000 $ 4.91 Share issuance (203,400 ) 4.91 Forfeited (59,400 ) 4.91 Balance, December 31, 2016 946,200 $ 4.91
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs	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 years ended December 31, 2016 , 2015 , and 2014 , there was no non-employee share-based compensation expense. Total stock-based compensation expense was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Income Statement Classification: Research and development expense $ 7,137 $ 5,578 $ 1,085 General and administrative expense 9,086 7,381 3,326 Total stock-based compensation expense $ 16,223 $ 12,959 $ 4,411

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate	A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2016 , 2015 , and 2014 (in thousands, except percentages): 2016 2015 2014 Amount % of Pretax Amount % of Pretax Amount % of Pretax Income tax benefit at statutory rate $ (25,973 ) 34.0 % $ (39,907 ) 34.0 % $ (20,166 ) 34.0 % State income taxes (1,544 ) 2.0 % (2,176 ) 1.9 % (1,343 ) 2.3 % Research and development credits (2,691 ) 3.5 % (5,698 ) 4.9 % (2,577 ) 4.3 % Foreign rate differential (2 ) — % 2 — % — — % Permanent items 2,537 (3.3 )% 3,687 (3.1 )% 1,525 (2.6 )% Provision to return adjustments 259 (0.3 )% (426 ) 0.2 % 64 (0.1 )% Effect of change in state tax rate 1,585 (2.1 )% 932 (0.8 )% 2 — % Increase in unrecognized tax benefits 444 (0.6 )% 950 (0.8 )% 425 (0.7 )% Change in valuation allowance 25,385 (33.2 )% 42,636 (36.3 )% 22,070 (37.2 )% Net benefit $ — — % $ — — % $ — — %
Components of Deferred Tax Assets and Liabilities	The components of deferred tax assets and liabilities at December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Domestic net operating loss carryforwards $ 114,111 $ 93,923 Foreign net operating loss carryforwards — 2 Research and development expenses 813 1,289 Capitalized Section 174 expenses 48 51 Research and development credits 10,907 8,889 Accrued bonuses 1,006 822 Share-based compensation 7,214 3,671 Other 460 604 Total gross deferred tax assets 134,559 109,251 Valuation allowance (134,496 ) (109,111 ) Total deferred tax assets 63 140 Deferred tax liabilities: Other (63 ) (140 ) Total deferred tax liabilities (63 ) (140 ) Total deferred tax assets and liabilities, net $ — $ —
Summary of Uncertain Tax Benefit	Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the years ended December 31, 2016 and 2015 , as follows (in thousands): Balance at December 31, 2014 $ 1,006 Increases related to 2015 940 Increases related to prior periods 10 Balance at December 31, 2015 1,956 Increases related to 2016 444 Increases related to prior periods — Balance at December 31, 2016 $ 2,400

Selected Quarterly Financial 25

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Schedule of Quarterly Financial Information	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2016 and 2015 are as follows (in thousands, except share and per share data): 2016 Quarters Fourth Third Second First Total revenues $ 1,980 $ 653 $ 1,841 $ 1,228 Operating loss (15,373 ) (17,422 ) (18,525 ) (26,632 ) Net loss (14,957 ) (17,025 ) (18,148 ) (26,260 ) Net loss per share, basic and diluted $ (0.32 ) $ (0.37 ) $ (0.39 ) $ (0.57 ) Weighted-average shares outstanding, basic and diluted 46,431,809 46,236,749 46,214,086 46,184,134 2015 Quarters Fourth Third Second First Total revenues $ 3,110 $ 2,271 $ 4,143 $ 1,238 Operating loss (38,223 ) (32,748 ) (24,951 ) (22,329 ) Net loss (37,842 ) (32,449 ) (24,815 ) (22,266 ) Net loss per share, basic and diluted $ (0.82 ) $ (0.70 ) $ (0.59 ) $ (0.54 ) Weighted-average shares outstanding, basic and diluted 46,151,384 46,059,112 42,079,716 41,220,989

The Business and Summary of S26

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. 17, 2016	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Redemption Restriction Period	18 months
Short-term investments, available-for-sale		$ 180,558		$ 199,729
Long-term investments		47,407		124,040
Common Stock
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Convertible preferred stock, shares issued upon conversion			1,071,429
Common Stock | 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			1,071,429
Fair value, measurements, recurring
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		50,830		19,795
Short-term investments, available-for-sale		180,558		199,729
Long-term investments		47,407		124,040
Total assets		278,795		343,564
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		15,733		19,795
Short-term investments, available-for-sale		173,108		175,214
Long-term investments		47,407		116,372
Total assets		236,248		311,381
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		35,097		0
Short-term investments, available-for-sale		7,450		23,030
Long-term investments		0		7,668
Total assets		42,547		30,698
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, available-for-sale		0		1,485
Long-term investments		0		0
Total assets		0		1,485
Fair value, measurements, recurring | Common Stock
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale		1,286
Fair value, measurements, recurring | Common Stock | 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		1,286
Fair value, measurements, recurring | Common Stock | 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
Fair value, measurements, recurring | Common Stock | 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
Fair value, measurements, recurring | Money market funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		15,733		19,795
Fair value, measurements, recurring | Money market funds | 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		15,733		19,795
Fair value, measurements, recurring | Money market funds | Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		0		0
Fair value, measurements, recurring | Money market funds | Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		0		0
Fair value, measurements, recurring | Certificates of deposit
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale		7,450		23,030
Long-term investments				7,668
Fair value, measurements, recurring | Certificates of deposit | 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
Long-term investments				0
Fair value, measurements, recurring | Certificates of deposit | 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		7,450		23,030
Long-term investments				7,668
Fair value, measurements, recurring | Certificates of deposit | 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
Fair value, measurements, recurring | U.S. Treasury securities
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Short-term investments, available-for-sale		171,822		175,214
Long-term investments		47,407		116,372
Fair value, measurements, recurring | U.S. Treasury securities | 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		171,822		175,214
Long-term investments		47,407		116,372
Fair value, measurements, recurring | U.S. Treasury securities | 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
Fair value, measurements, recurring | U.S. Treasury securities | 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
Fair value, measurements, recurring | 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				1,485
Fair value, measurements, recurring | Preferred 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]
Short-term investments, available-for-sale				0
Fair value, measurements, recurring | Preferred stock of U.S. corporation | 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
Fair value, measurements, recurring | Preferred stock of U.S. corporation | 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				$ 1,485
Fair value, measurements, recurring | Commercial paper
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		35,097
Fair value, measurements, recurring | Commercial paper | 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
Fair value, measurements, recurring | Commercial paper | Significant Other Observable Inputs (Level 2)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		35,097
Fair value, measurements, recurring | Commercial paper | Significant Unobservable Inputs (Level 3)
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Cash equivalents		$ 0

The Business and Summary of S27

The Business and Summary of Significant Accounting Policies (Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis) (Details) - Preferred stock of U.S. corporation - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning of period	$ 1,485	$ 1,781	$ 0
Investment acquired			1,545
Fair value increase/decrease recorded in other comprehensive loss	(371)	(296)	236
Ending of period	0	$ 1,485	$ 1,781
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ (1,114)

The Business and Summary of S28

The Business and Summary of Significant Accounting Policies (Schedule of Prepaid and Other Current Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Prepaid research and development expenses	$ 843	$ 4,165
Interest receivable	772	670
Prepaid insurance	389	385
Other prepaid expenses and current assets	841	851
Total prepaid expenses and other current assets	$ 2,845	$ 6,071

The Business and Summary of S29

The Business and Summary of Significant Accounting Policies (Schedule of Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Accrued compensation	$ 2,906	$ 2,939
Accrued research and development expenses	2,257	3,596
Other accrued liabilities	1,052	3,186
Total accrued liabilities	$ 6,215	$ 9,721

The Business and Summary of S30

The Business and Summary of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016USD ($)segmentshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2014USD ($)shares
Fair Value of Financial Instruments
Other than temporary impairment losses, investments	$ 0	$ 0	$ 0
Fair value inputs, discount for lack of marketability		10.00%
Fair value assumptions, exercise price (in USD per share) | $ / shares		$ 1.54
Fair value assumptions, expected dividend rate		0.00%
Fair value assumptions, expected term		168 days
Fair value assumptions, risk free interest rate		0.44%
Fair value assumptions, expected volatility rate		75.00%
Property and Equipment
Property and equipment, useful life, leasehold improvements	amortized over the shorter of the useful life of the asset or the term of the related lease
Impairment of long-lived assets	$ 0
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Defined contribution plan, cost recognized	$ 400,000	$ 300,000
Per share information:
Anti-dilutive securities excluded from the calculation loss per share (in shares) | shares	1,012,928	1,202,887	2,170,660
Segments
Number of operating segments | segment	1
Allowance for doubtful accounts	$ 0	$ 0
Income tax expense (benefit)	$ 0	0	$ 0
Minimum
Property and Equipment
Property and equipment, useful life	3 years
Maximum
Property and Equipment
Property and equipment, useful life	5 years
Fair Value, Measurements, Nonrecurring
Fair Value of Financial Instruments
Fair value adjustments, assets	$ 0
Fair value adjustments, liabilities	0
BARDA
Segments
Revenue from grants	0	$ 0	$ 0
Research and development expense
Segments
Prior period reclassification adjustments	$ 0

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Amortized Cost	$ 228,405	$ 324,533
Gross Unrealized Gains	20	2
Gross Unrealized Losses	(460)	(766)
Estimated Fair Value	227,965	323,769
Certificates of deposit
Schedule of Investments [Line Items]
Amortized Cost	7,445	30,724
Gross Unrealized Gains	5	2
Gross Unrealized Losses	0	(28)
Estimated Fair Value	7,450	30,698
U.S. Treasury securities
Schedule of Investments [Line Items]
Amortized Cost	219,415	292,264
Gross Unrealized Gains	15	0
Gross Unrealized Losses	(201)	(678)
Estimated Fair Value	219,229	291,586
Preferred stock of U.S. corporation
Schedule of Investments [Line Items]
Amortized Cost		1,545
Gross Unrealized Gains		0
Gross Unrealized Losses		(60)
Estimated Fair Value		$ 1,485
Common Stock
Schedule of Investments [Line Items]
Amortized Cost	1,545
Gross Unrealized Gains	0
Gross Unrealized Losses	(259)
Estimated Fair Value	$ 1,286

Investments - Summary of Invest

Investments - Summary of Investments with Unrealized Losses, Aggregated by Investment Type and the Length of Time (Details) $ in Thousands	Dec. 31, 2016USD ($)securities	Dec. 31, 2015USD ($)securities
Schedule of Investments [Line Items]
Fair Value, Less than 12 Months	$ 129,490	$ 317,521
Unrealized Loss, Less than 12 Months	(460)	(766)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	129,490	317,521
Unrealized Loss, Total	$ (460)	$ (766)
Number of securities with unrealized losses, Less than 12 Months | securities	24	180
Number of securities with unrealized losses, Greater than 12 Months | securities	0	0
Number of securities with unrealized losses, Total | securities	24	180
Certificates of deposit
Schedule of Investments [Line Items]
Fair Value, Less than 12 Months		$ 24,450
Unrealized Loss, Less than 12 Months		(28)
Fair Value, Greater than 12 Months		0
Unrealized Loss, Greater than 12 Months		0
Fair Value, Total		24,450
Unrealized Loss, Total		(28)
U.S. Treasury securities
Schedule of Investments [Line Items]
Fair Value, Less than 12 Months	$ 128,204	291,586
Unrealized Loss, Less than 12 Months	(201)	(678)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	128,204	291,586
Unrealized Loss, Total	(201)	(678)
Preferred stock of U.S. corporation
Schedule of Investments [Line Items]
Fair Value, Less than 12 Months		1,485
Unrealized Loss, Less than 12 Months		(60)
Fair Value, Greater than 12 Months		0
Unrealized Loss, Greater than 12 Months		0
Fair Value, Total		1,485
Unrealized Loss, Total		$ (60)
Common Stock
Schedule of Investments [Line Items]
Fair Value, Less than 12 Months	1,286
Unrealized Loss, Less than 12 Months	(259)
Fair Value, Greater than 12 Months	0
Unrealized Loss, Greater than 12 Months	0
Fair Value, Total	1,286
Unrealized Loss, Total	$ (259)

Investments - Available for Sal

Investments - Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Maturing in one year or less	$ 179,272
Maturing after one year through two years	47,407
Total debt investments	226,679
Total investments	227,965	$ 323,769
Common Stock
Schedule of Investments [Line Items]
Total investments	$ 1,286

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,837	$ 5,008
Less accumulated depreciation	(2,994)	(1,963)
Property and equipment, net of accumulated depreciation	2,843	3,045
Lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,419	1,946
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,570	1,463
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,262	1,063
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 586	$ 536

Loan Payable (Narrative) (Detai

Loan Payable (Narrative) (Details) - USD ($)	Jan. 27, 2012	Dec. 31, 2015
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity	$ 15,000,000
Loans payable, current		$ 0
First tranche
Line of Credit Facility [Line Items]
Loan and security agreement, maximum capacity	$ 3,000,000
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	$ 12,000,000
Interest only period	6 months
Principal and interest amortization period	32 months
Loan and security agreement, interest rate	8.25%

Commitments and Contingencies36

Commitments and Contingencies (Schedule of Future Minimum Rental Payments for Operating Leases) (Details) $ in Thousands	Dec. 31, 2016USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Minimum Rental Payment, 2017	$ 825
Minimum Rental Payment, 2018	759
Minimum Rental Payment, 2019	665
Minimum Rental Payment, 2020	672
Minimum Rental Payment, 2021	112
Total future minimum rental payments	$ 3,033

Commitments and Contingencies37

Commitments and Contingencies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Operating leases, rent expense	$ 700,000	$ 600,000	$ 400,000
Provision for refundable amount for federal research contract funds	$ 0	$ 0

Commitments and Contingencies38

Commitments and Contingencies (Schedule of Future Minimum Sublease Rental Payments for Operating Leases) (Details) (Details) $ in Thousands	Dec. 31, 2016USD ($)ft²
Commitments and Contingencies Disclosure [Abstract]
Area of sublease property | ft²	3,537
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Minimum Sublease Rental Payment, 2017	$ 60
Minimum Sublease Rental Payment, 2018	74
Minimum Sublease Rental Payment, 2019	77
Minimum Sublease Rental Payment, 2020	81
Minimum Sublease Rental Payment, 2021	14
Total future minimum sublease rental payments	$ 306

Stockholders' Equity (Deficit39

Stockholders' Equity (Deficit) (Schedule of Shares Reserved for Future Issuance) (Details) - shares	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	7,791,399	5,882,313
The 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	662,180	1,609,791
The 2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	1,612,759	1,298,333
Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	4,342,466	2,746,395
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	946,200	0
Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	227,794	227,794

Stockholders' Equity (Deficit40

Stockholders' Equity (Deficit) (Assumption Used to Determine the Fair Value of Options Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per option (in USD per share)	$ 5.62	$ 25.18	$ 14.01
Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	85.16%	66.89%	71.47%
Expected term (in years)	6 years	6 years	5 years 357 days
Weighted-average risk-free interest rate	1.70%	1.53%	1.91%
Expected dividend yield	0.00%	0.00%	0.00%
Weighted-average fair value per option (in USD per share)	$ 5.62	$ 25.18	$ 14.01

Stockholders' Equity (Deficit41

Stockholders' Equity (Deficit) (Summary of Activity Related to Stock Options) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options outstanding, Beginning balance	2,746,395	1,859,970
Number of options outstanding, Granted	2,418,551	1,249,683
Number of options outstanding, Exercised	(48,441)	(292,581)
Number of options outstanding, Forfeited	(774,039)	(70,677)
Number of options outstanding, Ending balance	4,342,466	2,746,395	1,859,970
Number of options outstanding, Exercisable	2,033,315
Number of options outstanding, Vested and expected to vest	4,275,950
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, Beginning balance (in USD per share)	$ 28.19	$ 15.79
Weighted-average exercise price, Granted (in USD per share)	7.76	41.80
Weighted-average exercise price, Exercised (in USD per share)	3.48	7.22
Weighted-average exercise price, Forfeited (in USD per share)	24.13	30.78
Weighted-average exercise price, Ending balance (in USD per share)	17.81	$ 28.19	$ 15.79
Weighted-average exercise price, Exercisable (in USD per share)	19.77
Weighted-average exercise price, Vested or expected to vest (in USD per share)	$ 17.83
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average remaining contractual life (in years), Beginning	8 years 1 month 2 days	8 years 4 months 28 days	8 years 5 months 16 days
Weighted-average remaining contractual life (in years), Exercisable	7 years 5 months 9 days
Weighted-average remaining contractual life (in years), Vested or expected to vest	8 years 29 days
Aggregate intrinsic value of options outstanding	$ 540,234
Aggregate intrinsic value of options exercisable	483,421
Aggregate intrinsic value of options vested or expected to vest	$ 537,904

Stockholders' Equity (Deficit42

Stockholders' Equity (Deficit) (Schedule of other information regarding stock options) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Weighted-average fair value per option (in USD per share)	$ 5.62	$ 25.18	$ 14.01
Total intrinsic value of options exercised	$ 119	$ 10,139	$ 30,438
Total fair value of shares vested	$ 13,330	$ 11,498	$ 4,696

Stockholders' Equity (Deficit43

Stockholders' Equity (Deficit) (Schedule of Share-based Compensation, Shares Authorized) (Details)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Exercise price range, $1.53 to 7.57
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	504,307
Share-based compensation, outstanding options, weighted average remaining contractual term	5 years 10 months 6 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 4
Share-based compensation, number of exercisable options (in shares) | shares	399,862
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 3.89
Exercise Price Range, $7.58 to 8.06
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	1,927,576
Share-based compensation, outstanding options, weighted average remaining contractual term	9 years 7 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 8.06
Share-based compensation, number of exercisable options (in shares) | shares	456,715
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 8.06
Exercise Price Range, $15.79 to 18.75
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	423,521
Share-based compensation, outstanding options, weighted average remaining contractual term	7 years 18 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 17.83
Share-based compensation, number of exercisable options (in shares) | shares	313,439
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 17.84
Exercise Price Range, $18.76 to 39.17
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	599,121
Share-based compensation, outstanding options, weighted average remaining contractual term	7 years 6 months 22 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 25.43
Share-based compensation, number of exercisable options (in shares) | shares	398,537
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 25.04
Exercise Price Range, $39.18 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	887,941
Share-based compensation, outstanding options, weighted average remaining contractual term	8 years 2 months 16 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 41.67
Share-based compensation, number of exercisable options (in shares) | shares	464,762
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 41.71
Exercise Price Range, $1.53 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of outstanding options (in shares) | shares	4,342,466
Share-based compensation, outstanding options, weighted average remaining contractual term	8 years 1 month 2 days
Share-based compensation, outstanding options, weighted average exercise price (in USD per share)	$ 17.81
Share-based compensation, number of exercisable options (in shares) | shares	2,033,315
Share-based compensation, exercisable options, weighted average exercise price (in USD per share)	$ 19.77
Minimum | Exercise price range, $1.53 to 7.57
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	1.53
Minimum | Exercise Price Range, $7.58 to 8.06
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	7.58
Minimum | Exercise Price Range, $15.79 to 18.75
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	15.79
Minimum | Exercise Price Range, $18.76 to 39.17
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	18.76
Minimum | Exercise Price Range, $39.18 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	39.18
Minimum | Exercise Price Range, $1.53 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, lower range limit (in USD per share)	1.53
Maximum | Exercise price range, $1.53 to 7.57
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	7.57
Maximum | Exercise Price Range, $7.58 to 8.06
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	8.06
Maximum | Exercise Price Range, $15.79 to 18.75
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	18.75
Maximum | Exercise Price Range, $18.76 to 39.17
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	39.17
Maximum | Exercise Price Range, $39.18 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	53.74
Maximum | Exercise Price Range, $1.53 to 53.74
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, upper range limit (in USD per share)	$ 53.74

Stockholders' Equity (Deficit44

Stockholders' Equity (Deficit) (Schedule of Share-Based Compensation) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per option (in USD per share), ESPP purchase rights	$ 5.62	$ 25.18	$ 14.01
The 2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, ESPP purchase rights	111.57%	57.77%	74.24%
Expected term (in years), ESPP purchase rights	1 year 135 days	1 year 1 month 24 days	9 months 18 days
Weighted-average risk-free interest rate, ESPP purchase rights	0.75%	0.43%	0.09%
Expected dividend yield, ESPP purchase rights	0.00%	0.00%	0.00%
Weighted-average fair value per option (in USD per share), ESPP purchase rights	$ 3.20	$ 22.10	$ 9.93

Stockholders' Equity (Deficit45

Stockholders' Equity (Deficit) (Summary of Activity Related to Restricted Stock Units) (Details)	12 Months Ended
	Dec. 31, 2016$ / sharesshares	Dec. 31, 2015shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Class of warrant or right, number of securities called by warrants or rights (in shares)	227,794	227,794
Number of Restricted Stock Units Outstanding
Forfeited (in shares)	(59,400)
Restricted stock units (RSUs)
Number of Restricted Stock Units Outstanding
Beginning Balance (in shares)	0
Granted (in shares)	1,209,000
Shares issuance (in shares)	(203,400)
Ending Balance (in shares)	946,200
Weighted-Average Grant-Date Fair Value
Granted (in USD per share) | $ / shares	$ 4.91
Shares issuance (in USD per share) | $ / shares	4.91
Forfeited (in USD per share) | $ / shares	4.91
Nonvested | $ / shares	$ 4.91
Executive Officer | Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	3 years
Non-executive | Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	1 year 6 months

Stockholders' Equity (Deficit46

Stockholders' Equity (Deficit) (Schedule of Allocation of Recognized Period Costs) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 16,223,000	$ 12,959,000	$ 4,411,000
Employee | Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	7,137,000	5,578,000	1,085,000
Employee | General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	9,086,000	7,381,000	3,326,000
Non-Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 0	$ 0	$ 0

Stockholders' Equity (Deficit47

Stockholders' Equity (Deficit) (Narrative) (Details) - USD ($)	Jan. 01, 2016	Jun. 16, 2015	Jan. 01, 2015	Nov. 05, 2014	Jun. 20, 2014	May 27, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Apr. 30, 2013	Feb. 28, 2013	Feb. 28, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants, outstanding (in shares)							227,794	227,794		227,794
Common stock, shares authorized							200,000,000	200,000,000		200,000,000
Common stock, shares, outstanding							46,522,475	46,162,525		46,522,475
Common stock, shares, issued							46,522,475	46,162,525		46,522,475
New issues of stock during period (in shares)								4,341,250
Offering price per share (in USD per share)								$ 39.75
Warrants to purchase common stock (in shares)							227,794	227,794		227,794
Proceeds from public offerings, net of offering costs							$ 0	$ 161,879,000	$ 225,938,000
Shares reserved for future issuance							7,791,399	5,882,313		7,791,399
Employees' contribution liabilities, ESPP							$ 6,215,000	$ 9,721,000		$ 6,215,000
Share-based compensation, cash received from exercise of stock options							600,000	3,200,000	5,000,000
Tax Benefit from share-based payment arrangements							$ 0	$ 0	$ 0
The 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be granted											1,408,450
Share-based compensation, equity increase					4.00%		2.50%
Share-based compensation, nonvested awards, compensation not yet recognized, stock options							$ 22,800,000			$ 22,800,000
Unrecognized compensation costs, period of recognition							2 years 102 days
Shares reserved for future issuance							662,180	1,609,791		662,180
The 2013 Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be granted							2,816,901			2,816,901
The 2012 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be granted											244,717
Share-based compensation, granted (in shares)										0
The 2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be granted												704,225
Share-based compensation, equity increase							1.00%
Number of shares authorized, increase amount							422,535
Number of additional shares authorized	422,535		410,317
Number of shares available for grant	1,803,726		1,381,191
Shares reserved for future issuance							1,612,759	1,298,333		1,612,759
Share-based compensation, maximum employee subscription rate							15.00%			15.00%
Discount from market price, entry date							15.00%
Discount from market price, purchase date							15.00%
Employee stock purchase plan, participation period							6 months
Employee stock purchase plan, automatic reset participation period							24 months
Shares issued during period, employee stock purchase plans							108,109	56,583
Employees' contribution liabilities, ESPP							$ 300,000			$ 300,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New issues of stock during period (in shares)		4,341,250		4,197,500		8,395,000
Offering price per share (in USD per share)		$ 39.75		$ 29		$ 14.22
Warrants to purchase common stock (in shares)											1,549,628
Proceeds from public offerings, net of offering costs		$ 161,900,000		$ 114,000,000		$ 111,800,000
Common Stock | IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant strike price (in USD per share)											$ 7.26
Common Stock | Over-allotment option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New issues of stock during period (in shares)		566,250		547,500		1,095,000
Series F
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants to purchase common stock (in shares)													5,501,215
Warrant strike price (in USD per share)													$ 2.045

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate) (Alternate) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax benefit at statutory rate	$ (25,973,000)	$ (39,907,000)	$ (20,166,000)
State income taxes	(1,544,000)	(2,176,000)	(1,343,000)
Research and development credits	(2,691,000)	(5,698,000)	(2,577,000)
Foreign rate differential	(2,000)	2,000	0
Permanent items	2,537,000	3,687,000	1,525,000
Provision to return adjustments	259,000	(426,000)	64,000
Effect of change in state tax rate	1,585,000	932,000	2,000
Increase in unrecognized tax benefits	444,000	950,000	425,000
Change in valuation allowance	25,385,000	42,636,000	22,070,000
Net benefit	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax benefit at statutory rate, tax rate	34.00%	34.00%	34.00%
State income taxes, tax rate	2.00%	1.90%	2.30%
Research and development credits, tax rate	3.50%	4.90%	4.30%
Foreign rate differential, tax rate	0.00%	0.00%	0.00%
Permanent items, tax rate	(3.30%)	(3.10%)	(2.60%)
Provision to return adjustments, tax rate	(0.30%)	0.20%	(0.10%)
Effect of change in state tax rate, tax rate	(2.10%)	(0.80%)	0.00%
Increase in unrecognized tax benefits, tax rate	(0.60%)	(0.80%)	(0.70%)
Change in valuation allowance, tax rate	(33.20%)	(36.30%)	(37.20%)
Net benefit, tax rate	0.00%	0.00%	0.00%

Income Taxes (Components of Def

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Domestic net operating loss carryforwards	$ 114,111	$ 93,923
Foreign net operating loss carryforwards	0	2
Research and development expenses	813	1,289
Capitalized Section 174 expenses	48	51
Research and development credits	10,907	8,889
Accrued bonuses	1,006	822
Share-based compensation	7,214	3,671
Other	460	604
Total gross deferred tax assets	134,559	109,251
Valuation allowance	(134,496)	(109,111)
Total deferred tax assets	63	140
Deferred tax liabilities:
Other	(63)	(140)
Total deferred tax liabilities	(63)	(140)
Total deferred tax assets and liabilities, net	$ 0	$ 0

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2007	Dec. 31, 2002
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ 0	$ 0	$ 0
Undistributed earnings of foreign subsidiary	0
Annual limitation of operating loss carryforwards	0.50			$ 6,700,000
Loss limitation ownership change benchmark amount					$ 762,000	$ 64,000
Unrecognized tax benefits, gross	2,400,000	1,956,000	$ 1,006,000
Penalties and interest accrued	0
Unrecognized tax benefits that would impact effective tax rate	0	0
Employee stock option
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	35,900,000
Domestic tax authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	356,100,000	296,600,000
Tax credit carryforward	14,500,000
State and local jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 287,200,000	$ 233,900,000

Income Taxes (Summary of Uncert

Income Taxes (Summary of Uncertain Tax Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 1,956	$ 1,006
Increase related to current year tax positions	444	940
Increase related to prior periods	0	10
Ending balance	$ 2,400	$ 1,956

Significant Agreements (Details

Significant Agreements (Details) $ in Thousands

Dec. 17, 2014USD ($)shares

Jan. 31, 2017shares

Dec. 31, 2016USD ($)

Apr. 30, 2015USD ($)

Feb. 28, 2011extension

May 31, 2002USD ($)shares

Dec. 31, 2016USD ($)period

Dec. 31, 2015USD ($)

Dec. 31, 2014USD ($)

Dec. 31, 2016USD ($)

Mar. 31, 2017USD ($)

Jun. 30, 2017USD ($)

Sep. 30, 2016shares

Long-term Purchase Commitment [Line Items]

Contract revenue

$ 5,702

$ 9,214

$ 4,040

Collaboration and licensing revenue

0

1,548

0

Estimated Fair Value

$ 227,965

$ 227,965

323,769

$ 227,965

Regents of University of California

Long-term Purchase Commitment [Line Items]

Expenses recognized

$ 60

Stock issued during period, issued for services | shares

64,788

BARDA

Long-term Purchase Commitment [Line Items]

Number of extension periods | extension

4

Contract revenue

51,700

Number Of Extension Periods Through Which Revenue Has Been Recognized | period

3

ContraVir Pharmaceuticals

Long-term Purchase Commitment [Line Items]

License agreement, termination notice period

60 days

Collaboration and licensing revenue

$ 1,500

The Regents of the University of Michigan

Long-term Purchase Commitment [Line Items]

License fees

50

Maximum | Regents of University of California

Long-term Purchase Commitment [Line Items]

Milestone payments

$ 3,400

Sublicense fee percentage

50.00%

Royalties percentage

50.00%

Maximum | ContraVir Pharmaceuticals

Long-term Purchase Commitment [Line Items]

Future licenses revenue

$ 20,000

Maximum | The Regents of the University of Michigan

Long-term Purchase Commitment [Line Items]

Royalties percentage

2.00%

Minimum | The Regents of the University of Michigan

Long-term Purchase Commitment [Line Items]

Royalties percentage

0.25%

Common Stock

Long-term Purchase Commitment [Line Items]

Convertible preferred stock, shares issued upon conversion | shares

1,071,429

Estimated Fair Value

1,286

$ 1,286

1,286

Common Stock | ContraVir Pharmaceuticals

Long-term Purchase Commitment [Line Items]

Estimated Fair Value

$ 1,300

$ 1,300

$ 1,300

Preferred stock of U.S. corporation

Long-term Purchase Commitment [Line Items]

Estimated Fair Value

1,485

Preferred stock of U.S. corporation | ContraVir Pharmaceuticals

Long-term Purchase Commitment [Line Items]

Shares received as consideration for license agreement | shares

120,000

Value of shares received as consideration for license agreement

$ 1,500

Estimated Fair Value

$ 1,500

Scenario, Forecast | Maximum | BARDA

Long-term Purchase Commitment [Line Items]

Reimbursement revenue

$ 75,800

Fees and commissions

5,300

Scenario, Forecast | Second Option Segment | Maximum | BARDA

Long-term Purchase Commitment [Line Items]

Contract revenue

$ 17,500

Scenario, Forecast | Third Option Segment | Maximum | BARDA

Long-term Purchase Commitment [Line Items]

Contract revenue

$ 13,000

Brincidofovir | Maximum | Regents of University of California

Long-term Purchase Commitment [Line Items]

Sublicense fee amount payable fee percentage

5.00%

Stated Value | Preferred stock of U.S. corporation | ContraVir Pharmaceuticals

Long-term Purchase Commitment [Line Items]

Value of shares received as consideration for license agreement

$ 1,200

Subsequent Event | The Regents of the University of Michigan

Long-term Purchase Commitment [Line Items]

Stock issued during period, issued for services | shares

33,058

Selected Quarterly Financial 53

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 1,980	$ 653	$ 1,841	$ 1,228	$ 3,110	$ 2,271	$ 4,143	$ 1,238	$ 5,702	$ 10,762	$ 4,040
Operating loss	(15,373)	(17,422)	(18,525)	(26,632)	(38,223)	(32,748)	(24,951)	(22,329)	(77,952)	(118,251)	(58,866)
Net loss	$ (14,957)	$ (17,025)	$ (18,148)	$ (26,260)	$ (37,842)	$ (32,449)	$ (24,815)	$ (22,266)	$ (76,390)	$ (117,372)	$ (59,312)
Net loss per share, basic and diluted (in USD per share)	$ (0.32)	$ (0.37)	$ (0.39)	$ (0.57)	$ (0.82)	$ (0.70)	$ (0.59)	$ (0.54)	$ (1.65)	$ (2.67)	$ (1.80)
Weighted-average shares outstanding, basic and diluted (in shares)	46,431,809	46,236,749	46,214,086	46,184,134	46,151,384	46,059,112	42,079,716	41,220,989	46,267,064	43,878,326	33,003,714