Novavax (NVAX) 10-K 14 Mar 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 09, 2018	Jun. 30, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Entity Registrant Name	NOVAVAX INC
Entity Central Index Key	1,000,694
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 328,500,000
Trading Symbol	NVAX
Entity Common Stock, Shares Outstanding		343,742,084

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 106,307	$ 144,353
Marketable securities	50,996	91,126
Restricted cash	28,234	30,314
Prepaid expenses and other current assets	17,774	22,037
Total current assets	203,311	287,830
Restricted cash	890	4,590
Property and equipment, net	35,987	40,184
Intangible assets, net	7,873	9,225
Goodwill	53,563	51,673
Other non-current assets	869	799
Total assets	302,493	394,301
Current liabilities:
Accounts payable	5,613	5,685
Accrued expenses	29,610	24,508
Accrued interest	5,078	5,078
Deferred revenue	25,625	30,079
Other current liabilities	7,749	1,056
Total current liabilities	73,675	66,406
Deferred revenue	2,500	2,500
Convertible notes payable	317,763	316,339
Other non-current liabilities	10,287	14,602
Total liabilities	404,225	399,847
Commitments and contingencies
Stockholders’ deficit:
Preferred stock, $0.01 par value, 2,000,000 shares authorized; no shares issued and outstanding at December 31, 2017 and 2016	0	0
Common stock, $0.01 par value, 600,000,000 shares authorized at December 31, 2017 and 2016; and 323,684,820 shares issued and 323,229,390 shares outstanding at December 31, 2017 and 271,701,397 shares issued and 271,245,967 shares outstanding at December 31, 2016	3,237	2,717
Additional paid-in capital	1,020,457	935,997
Accumulated deficit	(1,114,359)	(929,996)
Treasury stock, 455,430 shares, cost basis at both December 31, 2017 and 2016	(2,450)	(2,450)
Accumulated other comprehensive loss	(8,617)	(11,814)
Total stockholders’ deficit	(101,732)	(5,546)
Total liabilities and stockholders’ deficit	$ 302,493	$ 394,301

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, par or stated value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	323,684,820	271,701,397
Common stock, shares outstanding	323,229,390	271,245,967
Treasury stock, shares	455,430	455,430

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Government contract	$ 0	$ 2,184	$ 33,344
Grant and other	31,176	13,169	2,906
Total revenue	31,176	15,353	36,250
Expenses:
Research and development	168,435	237,939	162,644
General and administrative	34,451	46,527	30,842
Total expenses	202,886	284,466	193,486
Loss from operations	(171,710)	(269,113)	(157,236)
Other income (expense):
Investment income	1,946	2,143	660
Interest expense	(14,072)	(12,965)	(241)
Other income (expense)	67	(31)	(120)
Net loss	$ (183,769)	$ (279,966)	$ (156,937)
Basic and diluted net loss per share	$ (0.63)	$ (1.03)	$ (0.6)
Basic and diluted weighted average number of common shares outstanding	292,669	270,802	262,248

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss	$ (183,769)	$ (279,966)	$ (156,937)
Other comprehensive income (loss):
Net unrealized (losses) gains on marketable securities available-for-sale	(50)	54	42
Foreign currency translation adjustment	3,247	(2,744)	(2,561)
Other comprehensive income (loss)	3,197	(2,690)	(2,519)
Comprehensive loss	$ (180,572)	$ (282,656)	$ (159,456)

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance beginning at Dec. 31, 2014	$ 229,618	$ 2,393	$ 729,373	$ (493,093)	$ (2,450)	$ (6,605)
Balance beginning (in shares) at Dec. 31, 2014		239,287,294
Non-cash compensation cost for stock options, ESPP and restricted stock	13,431	$ 0	13,431	0	0	0
Exercise of stock options/Purchases under ESPP	4,801	$ 19	4,782	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,950,748
Restricted stock issued as compensation	0	$ 0	0	0	0	0
Restricted stock issued as compensation, shares		25,000
Issuance of common stock, net of issuance costs	204,275	$ 292	203,983	0	0	0
Issuance of common stock, net of issuance costs, shares		29,163,620
Unrealized gain (loss) on marketable securities	42	$ 0	0	0	0	42
Foreign currency translation adjustment	(2,561)	0	0	0	0	(2,561)
Net loss	(156,937)	0	0	(156,937)	0	0
Balance ending at Dec. 31, 2015	292,669	$ 2,704	951,569	(650,030)	(2,450)	(9,124)
Balance ending (in shares) at Dec. 31, 2015		270,426,662
Non-cash compensation cost for stock options, ESPP and restricted stock	19,160	$ 0	19,160	0	0	0
Exercise of stock options/Purchases under ESPP	3,802	$ 13	3,789	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,254,735
Restricted stock issued as compensation	0	$ 0	0	0	0	0
Restricted stock issued as compensation, shares		20,000
Payment of capped call transactions and costs	(38,521)	$ 0	(38,521)	0	0	0
Unrealized gain (loss) on marketable securities	54	0	0	0	0	54
Foreign currency translation adjustment	(2,744)	0	0	0	0	(2,744)
Net loss	(279,966)	0	0	(279,966)	0	0
Balance ending at Dec. 31, 2016	(5,546)	$ 2,717	935,997	(929,996)	(2,450)	(11,814)
Balance ending (in shares) at Dec. 31, 2016		271,701,397
Non-cash compensation cost for stock options, ESPP and restricted stock	19,809	$ 0	19,809	0	0	0
Exercise of stock options/Purchases under ESPP	1,152	$ 11	1,141	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,093,513
Issuance of common stock, net of issuance costs	63,425	$ 509	62,916	0	0	0
Issuance of common stock, net of issuance costs, shares		50,889,910
Unrealized gain (loss) on marketable securities	(50)	$ 0	0	0	0	(50)
Foreign currency translation adjustment	3,247	0	0	0	0	3,247
Net loss	(183,769)	0	0	(183,769)	0	0
Balance ending at Dec. 31, 2017	(101,732)	$ 3,237	1,020,457	(1,114,359)	(2,450)	(8,617)
Balance ending (in shares) at Dec. 31, 2017		323,684,820
Cumulative effect of adoption of ASU 2016-09	$ 0	$ 0	$ 594	$ (594)	$ 0	$ 0

CONSOLIDATED STATEMENTS OF CHA7

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Issuance of common stock, issuance costs	$ 1,065	$ 11,912

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net loss	$ (183,769)	$ (279,966)	$ (156,937)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	9,817	8,505	5,983
Loss on disposal of property and equipment	269	374	681
Amortization of debt issuance costs	1,424	1,305	0
Lease incentives received	1,933	1,963	2,792
Non-cash stock-based compensation	19,809	19,160	13,431
Other	2,715	663	1,460
Changes in operating assets and liabilities:
Restricted cash	5,780	3,301	(36,204)
Prepaid expenses and other assets	2,590	(1,119)	(1,790)
Accounts payable and accrued expenses	5,192	(4,808)	9,075
Deferred revenue	(4,456)	(6,057)	36,140
Other liabilities	0	1,212	(721)
Net cash used in operating activities	(138,696)	(255,467)	(126,090)
Investing Activities:
Capital expenditures	(4,189)	(18,202)	(18,268)
Purchases of marketable securities	(218,045)	(356,556)	(228,521)
Proceeds from maturities of marketable securities	258,202	402,775	225,519
Net cash provided by (used in) investing activities	35,968	28,017	(21,270)
Financing Activities:
Principal payments of capital leases	(37)	(71)	(67)
Principal payments of notes payable	0	(395)	(600)
Changes in restricted cash	0	(819)	(126)
Proceeds from issuance of convertible notes	0	325,000	0
Payments of costs related to issuance of convertible notes	0	(9,966)	0
Payments for capped call transactions and costs	0	(38,521)	0
Net proceeds from sales of common stock	63,425	0	204,275
Proceeds from the exercise of stock options and employee stock purchases	1,152	3,802	4,801
Net cash provided by financing activities	64,540	279,030	208,283
Effect of exchange rate on cash and cash equivalents	142	(335)	(150)
Net (decrease) increase in cash and cash equivalents	(38,046)	51,245	60,773
Cash and cash equivalents at beginning of year	144,353	93,108	32,335
Cash and cash equivalents at end of year	106,307	144,353	93,108
Supplemental disclosure of non-cash activities:
Capital expenditures included in accounts payable and accrued expenses	15	697	2,797
Supplemental disclosure of cash flow information:
Cash interest payments	$ 12,188	$ 6,189	$ 96

Organization

Organization	12 Months Ended
	Dec. 31, 2017
Organization [Abstract]
Organization	Note 1 – Organization Novavax, Inc. (“Novavax,” and together with its wholly owned subsidiary, Novavax AB, the “Company”) is a clinical-stage biotechnology company focused on the discovery, development and commercialization of recombinant nanoparticle vaccines and adjuvants. Using innovative proprietary recombinant nanoparticle vaccine technology, and its proprietary saponin-based adjuvant technology, the Company produces vaccine candidates to efficiently and effectively respond to both known and emerging disease threats. The Company’s vaccine candidates are genetically engineered three-dimensional nanostructures that incorporate recombinant proteins critical to disease pathogenesis and may elicit differentiated immune responses, which may be more efficacious than naturally occurring immunity or traditional vaccine. The Company’s product pipeline targets a variety of infectious diseases, with clinical vaccine candidates for respiratory syncytial virus (“RSV”), influenza and Ebola virus (“EBOV”), and preclinical programs for other infectious disease vaccine candidates.

Liquidity

Liquidity	12 Months Ended
	Dec. 31, 2017
Organization [Abstract]
Liquidity	Note 2 – Liquidity The Company’s vaccine candidates currently under development, some of which include adjuvants, will require significant additional research and development efforts that include extensive preclinical studies and clinical testing, and regulatory approval prior to commercial use. As a clinical-stage biotechnology company, the Company has primarily funded its operations with proceeds from the sale of its common stock in equity offerings, the issuance of convertible debt, revenue under its former contract with the Department of Health and Human Services, Biomedical Advanced Research and Development Authority (“HHS BARDA”) and more recently, revenue under the grant agreement (“Grant Agreement”) with the Bill & Melinda Gates Foundation (“BMGF”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 3 – Summary of Significant Accounting Policies The consolidated financial statements include the accounts of Novavax, Inc. and its wholly owned subsidiary, Novavax AB. All intercompany accounts and transactions have been eliminated in consolidation. The preparation of the consolidated financial statements in conformity with accounting principles generally accepted in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates. 2017 2016 Cash $ 10,482 $ 17,481 Money market funds 36,762 95,896 Asset-backed securities 16,007 19,000 Corporate debt securities 43,056 11,976 Cash and cash equivalents $ 106,307 $ 144,353 Cash equivalents are recorded at cost, which approximate fair value due to their short-term nature. Marketable securities consist of commercial paper, asset-backed securities and corporate notes. Classification of marketable securities between current and non-current is dependent upon the maturity date at the balance sheet date taking into consideration the Company’s ability and intent to hold the investment to maturity. Interest and dividend income is recorded when earned and included in investment income in the consolidated statements of operations. Premiums and discounts, if any, on marketable securities are amortized or accreted to maturity and included in investment income in the consolidated statements of operations. The specific identification method is used in computing realized gains and losses on the sale of the Company’s securities. The Company classifies its marketable securities with readily determinable fair values as “available-for-sale.” Investments in securities that are classified as available-for-sale are measured at fair market value in the consolidated balance sheets, and unrealized holding gains and losses on marketable securities are reported as a separate component of stockholders’ deficit until realized. Marketable securities are evaluated periodically to determine whether a decline in value is “other-than-temporary.” The term “other-than-temporary” is not intended to indicate a permanent decline in value. Rather, it means that the prospects for a near term recovery of value are not necessarily favorable, or that there is a lack of evidence to support fair values equal to, or greater than, the carrying value of the security. Management reviews criteria, such as the magnitude and duration of the decline, as well as the Company’s ability to hold the securities until market recovery, to predict whether the loss in value is other-than-temporary. If a decline in value is determined to be other-than-temporary, the value of the security is reduced and the impairment is recorded as other income (expense) in the consolidated statements of operations. Financial instruments, which possibly expose the Company to concentration of credit risk, consist primarily of cash and cash equivalents and marketable securities. The Company’s investment policy limits investments to certain types of instruments, including asset-backed securities, high-grade corporate debt securities and money market funds, places restrictions on maturities and concentrations in certain industries and requires the Company to maintain a certain level of liquidity. At times, the Company maintains cash balances in financial institutions, which may exceed federally insured limits. The Company has not experienced any losses relating to such accounts and believes it is not exposed to a significant credit risk on its cash and cash equivalents. The Company applies Accounting Standards Codification (“ASC”) Topic 820, Fair Value Measurements and Disclosures ASC 820 discusses valuation techniques, such as the market approach (comparable market prices), the income approach (present value of future income or cash flow) and the cost approach (cost to replace the service capacity of an asset or replacement cost). The statement utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The following is a brief description of those three levels: · Level 1: Observable inputs such as quoted prices (unadjusted) in active markets for identical assets or liabilities. · Level 2: Inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. · Level 3: Unobservable inputs that reflect the reporting entity’s own assumptions. The Company’s current and non-current restricted cash includes payments received under the Grant Agreement (see Note 7) and cash collateral accounts under letters of credit that serve as security deposits for certain facility leases. The Company will utilize the funds from the Grant Agreement as it incurs expenses for services performed under the agreement. At December 31, 2017 and 2016, the restricted cash balances (both current and non-current) consist of payments received under the Grant Agreement of $ 27.4 33.2 1.7 Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Amortization of leasehold improvements is computed using the straight-line method over the shorter of the estimated useful lives of the improvements or the remaining term of the lease. Repairs and maintenance costs are expensed as incurred. Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable based on the criteria for accounting for the impairment or disposal of long-lived assets under ASC Topic 360, Property, Plant and Equipment. Goodwill is subject to impairment tests annually or more frequently should indicators of impairment arise. The Company has determined that, because its only business is the development of recombinant vaccines, it operates as a single operating segment and has one reporting unit. The Company utilizes primarily the market approach and, if considered necessary, the income approach to determine if it has an impairment of its goodwill. The market approach is based on market value of invested capital. To ensure that the Company’s capital stock is the appropriate measurement of fair value, the Company considers factors such as its trading volume, diversity of investors and analyst coverage. If considered necessary, the income approach is used to corroborate the results of the market approach. Goodwill impairment may exist if the carrying value of the reporting unit exceeds its estimated fair value. If the carrying value of the reporting unit exceeds its fair value, step two of the impairment analysis is performed. In step two of the analysis, an impairment loss is recorded equal to the excess of the carrying value of the reporting unit’s goodwill over its implied fair value, should such a circumstance arise. At December 31, 2017 and 2016, the Company used the market approach to determine if the Company had an impairment of its goodwill. The fair value of the Company’s single reporting unit was substantially higher than its carrying value, resulting in no impairment to goodwill at December 31, 2017 and 2016. The Company’s intangible assets include proprietary adjuvant technology and collaboration agreements, which were measured at their estimated fair values as of their acquisition dates. Amortization expense for intangible assets is recorded on a straight-line basis over the expected useful lives of the assets, ranging from seven to 20 The Company has an equity investment in CPL Biologicals Private Limited (“CPLB”). The Company accounts for this investment using the equity method (see Note 7). Under the equity method of accounting, investments are stated at initial cost and are adjusted for subsequent additional investments and the Company’s proportionate share of earnings or losses and distributions up to the amount initially invested or advanced. The Company performs research and development for U.S. Government agencies and on behalf of grantors and other collaborators under cost reimbursable and fixed price contracts, including license, grant and clinical development agreements. The Company recognizes revenue under research contracts when a contract has been executed, the contract price is fixed or determinable, delivery of services or products has occurred and collection of the contract price is reasonably assured. Payments received in advance of work performed are recorded as deferred revenue and losses on contracts, if any, are recognized in the period in which they become known. Under its Grant Agreement with BMGF (see Note 7), the Company is reimbursed for certain costs that support development activities, including the Company’s global Phase 3 clinical trial in pregnant women in their third trimester, product licensing efforts and efforts to obtain World Health Organization (“WHO”) prequalification of its RSV F Vaccine. Payments received under the Grant Agreement are recognized as revenue in the period in which such research and development activities are performed. The Company analyzes its grant agreements to determine whether the payments received should be recorded as revenue or as a reduction to research and development expenses. In reaching this determination, management considers a number of factors, including whether the Company is principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s core operations. Historically, payments received under grant agreements have been recognized as revenue since the Company acts as a principal in the arrangement and the activities are core to its operations. Under cost reimbursable contracts with U.S. Government agencies, the Company is reimbursed and recognizes revenue as allowable costs are incurred plus a portion of the fixed-fee earned. The Company considers fixed-fees under cost reimbursable contracts to be earned in proportion to the allowable costs incurred in performance of the work as compared to total estimated contract costs, with such costs incurred representing a reasonable measurement of the proportional performance of the work completed. Under its HHS BARDA contract (see Note 7), certain activities were pre-approved by HHS BARDA in order for their costs to be deemed allowable direct costs. Direct costs incurred under cost reimbursable contracts are recorded as research and development expenses. Payments to the Company under cost reimbursable contracts with agencies of the U.S. Government, such as the HHS BARDA contract, are provisional payments subject to adjustment upon audit by the government. When the final determination of the additional reimbursable costs for any year has been made, and such amount is known and collection of the amount is reasonably assured, revenue and billings will be adjusted accordingly. Revenue associated with upfront payments under arrangements is recognized over the contract term or when all obligations associated with the upfront payment have been satisfied. The Company accounts for stock-based compensation related to grants of stock options, restricted stock awards and purchases under its Employee Stock Purchase Plan (the “ESPP”) at fair value. The Company recognizes compensation expense related to such awards on a straight-line basis over the requisite service period (generally the vesting period) of the equity awards, which typically occurs ratably over periods ranging from six months to four years. Effective January 1, 2017, the Company accounts for forfeitures when they occur. See Note 11 for a further discussion on stock-based compensation. The expected term of stock options granted was based on the Company’s historical option exercise experience and post-vesting forfeiture experience using the historical expected term from the vesting date, whereas the expected term for purchases under the ESPP was based on the purchase periods included in the offering. The expected volatility was determined using historical volatilities based on stock prices over a look-back period corresponding to the expected term. The risk-free interest rate was determined using the yield available for zero-coupon U.S. Government issues with a remaining term equal to the expected term. The Company has never paid a dividend, and as such, the dividend yield is zero, and the Company does not intend to pay dividends in the foreseeable future. Restricted stock awards have been recorded as compensation expense over the expected vesting period based on the fair value at the award date using the straight-line method of amortization. The Company accounts for share-based awards issued to non-employees by determining the fair value of equity awards given as consideration for services rendered to be recognized as compensation expense over the shorter of the vesting or service periods. In cases where an equity award is not fully vested, such equity award is revalued on each subsequent reporting date until vesting is complete with a cumulative catch-up adjustment recognized for any changes in its estimated fair value. Research and development expenses include salaries, stock-based compensation, laboratory supplies, consultants and subcontractors, including external contract research organizations (“CROs”), and other expenses associated with the Company’s process development, manufacturing, clinical, regulatory and quality assurance activities for its programs. In addition, related indirect costs such as, fringe benefits and overhead expenses, are also included in research and development expenses. Research and development activities are expensed as incurred. Accrued Research and Development Expenses The Company accrues research and development expenses, including clinical trial-related expenses, as the services are performed, which may include estimates of those expenses incurred, but not invoiced. The Company uses information provided by third-party service providers and CROs, invoices and internal estimates to determine the progress of work performed on the Company’s behalf. Assumptions based on clinical trial protocols, contracts and participant enrollment data are also developed to determine and analyze these estimates and accruals. The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes Tax benefits associated with uncertain tax positions are recognized in the period in which one of the following conditions is satisfied: (1) the more likely than not recognition threshold is satisfied; (2) the position is ultimately settled through negotiation or litigation; or (3) the statute of limitations for the taxing authority to examine and challenge the position has expired. Tax benefits associated with an uncertain tax position are reversed in the period in which the more likely than not recognition threshold is no longer satisfied. Interest and penalties related to income tax matters are recorded as income tax expense. At December 31, 2017 and 2016, the Company had no accruals for interest or penalties related to income tax matters. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was enacted into law, and the new legislation contains certain key tax provisions that affected the Company, including a reduction of the corporate income tax rate from 35 21 Income Tax Accounting Implications of the Tax Cuts and Jobs Act Net loss per share is computed using the weighted average number of shares of common stock outstanding. At December 31, 2017, 2016 and 2015, the Company had outstanding stock options and unvested restricted stock awards totaling 46,513,399 39,277,732 23,832,545 47,716,900 The accompanying consolidated financial statements are presented in U.S. dollars. The functional currency of Novavax AB, which is located in Sweden, is the local currency (Swedish Krona). The translation of assets and liabilities of Novavax AB to U.S. dollars is made at the exchange rate in effect at the consolidated balance sheet date, while equity accounts are translated at historical rates. The translation of the statement of operations data is made at the average exchange rate in effect for the period. The translation of operating cash flow data is made at the average exchange rate in effect for the period, and investing and financing cash flow data is translated at the exchange rate in effect at the date of the underlying transaction. Translation gains and losses are recognized as a component of accumulated other comprehensive loss in the accompanying consolidated balance sheets. The foreign currency translation adjustment balance included in accumulated other comprehensive loss was $ 8.6 11.8 The Company manages its business as one operating segment: the development of recombinant vaccines. The Company does not operate separate lines of business with respect to its vaccine candidates. Accordingly, the Company does not have separately reportable segments as defined by ASC Topic 280, Segment Reporting Recently Adopted In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Compensation - Stock Compensation (Topic 718) 0.6 Not Yet Adopted In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350)

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements [Abstract]
Fair Value Measurements	Note 4– Fair Value Measurements Fair Value at December 31, 2017 Fair Value at December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Money market funds(1) $ 36,762 $ — $ — $ 95,896 $ — $ — Asset-backed securities(2) — 29,750 — — 42,632 — Corporate debt securities(3) — 80,309 — — 79,470 — Total cash equivalents and marketable securities $ 36,762 $ 110,059 $ — $ 95,896 $ 122,102 $ — Liabilities Convertible notes payable $ — $ 152,396 $ — $ — $ 141,989 $ — (1) Classified as cash and cash equivalents as of December 31, 2017 and 2016, respectively (see Note 3). (2) Includes $ 16,007 19,000 (3) Includes $ 43,056 11,976 Fixed-income investments categorized as Level 2 are valued at the custodian bank by a third-party pricing vendor’s valuation models that use verifiable observable market data, e.g., interest rates and yield curves observable at commonly quoted intervals and credit spreads, bids provided by brokers or dealers or quoted prices of securities with similar characteristics. Pricing of the Company’s Notes (see Note 9) has been estimated using other observable inputs, including the price of the Company’s common stock, implied volatility, interest rates and credit spreads among others. Over time, the Company expects a market for the Notes to develop. At that time, the Company intends to use trade data as the principal basis for measuring fair value. During the years ended December 31, 2017 and 2016, the Company did not have any transfers between Levels. The amount in the Company’s consolidated balance sheets for accounts payable approximates its fair value due to its short-term nature. The Company’s milestone payment due to Wyeth (see Note 14) also approximates its fair value at December 31, 2017.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2017
Investments [Abstract]
Marketable Securities	Note 5 – Marketable Securities December 31, 2017 December 31, 2016 Amortized Gross Gross Fair Value Amortized Gross Gross Fair Asset-backed securities $ 13,748 $ — $ (5) $ 13,743 $ 23,636 $ — $ (4) $ 23,632 Corporate debt securities 37,265 — (12) 37,253 67,457 43 (6) 67,494 Total $ 51,013 $ — $ (17) $ 50,996 $ 91,093 $ 43 $ (10) $ 91,126 Marketable Securities – Unrealized Losses The Company owned 19 18 0.1

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Other Intangible Assets [Abstract]
Goodwill and Other Intangible Assets	Note 6 – Goodwill and Other Intangible Assets Goodwill Year Ended 2017 2016 Beginning balance $ 51,673 $ 53,065 Currency translation 1,890 (1,392) Ending balance $ 53,563 $ 51,673 Identifiable Intangible Assets December 31, 2017 December 31, 2016 Gross Accumulated Intangible Gross Accumulated Intangible Finite-lived intangible assets: Proprietary adjuvant technology $ 9,086 $ (2,006) $ 7,080 $ 8,222 $ (1,404) $ 6,818 Collaboration agreements 4,103 (3,310) 793 3,713 (1,306) 2,407 Total identifiable intangible assets $ 13,189 $ (5,316) $ 7,873 $ 11,935 $ (2,710) $ 9,225 Amortization expense for the years ended December 2017, 2016 and 2015 was $ 2.2 0.8 0.9 Year Amount 2018 $ 761 2019 761 2020 633 2021 454 2022 454

Grant, U.S. Government Contract

Grant, U.S. Government Contract and Joint Venture	12 Months Ended
	Dec. 31, 2017
Collaboration, U.S. Government Agreement and Joint Venture [Abstract]
Grant, U.S. Government Contract and Joint Venture	Note 7 – Grant, U.S. Government Contract and Joint Venture Bill & Melinda Gates Foundation Grant Agreement In support of the Company’s development of its RSV F Vaccine for infants via maternal immunization, in September 2015, the Company entered into the Grant Agreement with BMGF, under which it was awarded a grant totaling up to $ 89.1 Payments received in advance that are related to future performance are deferred and recognized as revenue when the research and development activities are performed. Cash payments received under the Grant are restricted as to their use until expenditures contemplated in the Grant are incurred. In 2017, the Company recognized revenue from the Grant of $ 29.7 42 HHS BARDA Contract for Recombinant Influenza Vaccines HHS BARDA awarded the Company a contract in 2011, which funded the development of both the Company’s quadrivalent seasonal and pandemic influenza virus-like particle (“VLP”) vaccine candidates. The contract with HHS BARDA was a cost-plus-fixed-fee contract, which reimbursed the Company for allowable direct contract costs incurred plus allowable indirect costs and a fixed-fee earned in the ongoing clinical development and product scale-up of its multivalent seasonal and monovalent pandemic H7N9 influenza VLP vaccine candidates. In September 2014, HHS BARDA exercised and initiated a two-year option to the contract, which included scope to support development activities leading up to planned Phase 3 clinical studies, added $ 70 97 7.7 The HHS BARDA contract expired in accordance with its terms in . 114 CPLB Joint Venture In 2009, the Company formed a joint venture with Cadila Pharmaceuticals Limited (“Cadila”), CPLB, to develop and manufacture vaccines, biological therapeutics and diagnostics in India. CPLB is owned 20 80

Other Financial Information

Other Financial Information	12 Months Ended
	Dec. 31, 2017
Other Financial Information [Abstract]
Other Financial Information	Note 8 – Other Financial Information Prepaid Expenses and Other Current Assets 2017 2016 Laboratory supplies $ 13,085 $ 15,736 Other prepaid expenses and other current assets 4,689 6,301 Prepaid expenses and other current assets $ 17,774 $ 22,037 Property and Equipment, net 2017 2016 Machinery and equipment $ 35,409 $ 32,596 Leasehold improvements 23,664 22,642 Computer hardware 5,091 4,285 Construction in progress 1,129 2,938 65,293 62,461 Less — accumulated depreciation (29,306) (22,277) Property and equipment, net $ 35,987 $ 40,184 Depreciation expense was approximately $ 7.6 7.7 5.1 Accrued Expenses 2017 2016 Employee benefits and compensation $ 11,186 $ 7,300 Research and development accruals 17,542 15,744 Other accrued expenses 882 1,464 Accrued expenses $ 29,610 $ 24,508

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	Note 9 – Long-Term Debt Convertible Notes In the first quarter of 2016, the Company issued $ 325 February 1, 2023 315.0 3.75 The Notes are not redeemable prior to maturity and are convertible into shares of the Company’s common stock. The Notes are initially convertible into approximately 47,716,900 shares of the Company’s common stock based on the initial conversion rate of 146.8213 shares of the Company’s common stock per $1,000 principal amount of the Notes. 6.81 22.5 5.56 In addition, the holders of the Notes may require the Company to repurchase the Notes at par value plus accrued and unpaid interest following the occurrence of a Fundamental Change (as described in the Indenture). If a holder of the Notes converts upon a Make-Whole Adjustment Event (as described in the Indenture), they may be eligible to receive a make-whole premium through an increase to the conversion rate up to a maximum of 179.8561 shares per $1,000 principal amount of Notes (subject to other adjustments as described in the Indenture). The Notes are accounted for in accordance with ASC 470-20, Debt with Conversion and Other Options Contracts in Entity’s Own Equity In connection with the issuance of the Notes, the Company also paid $ 38.5 9.73 75 5.56 Derivatives and Hedging - Overall The Company incurred approximately $ 10.0 0.9 December 31, December 31, Principal amount of Notes $ 325,000 $ 325,000 Unamortized debt issuance costs (7,237) (8,661) Total convertible notes payable $ 317,763 $ 316,339 Interest expense incurred in connection with the Notes consisted of the following for the years ended December 31 (in thousands): 2017 2016 Coupon interest $ 12,188 $ 11,240 Amortization of debt issuance costs 1,424 1,305 Total interest expense on Notes $ 13,612 $ 12,545

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity [Abstract]
Stockholders' Equity	Note 10 – Stockholders’ Equity In December 2017, the Company entered into an At Market Issuance Sales Agreement (“December 2017 Sales Agreement”), which allows it to issue and sell up to $ 75 12.7 26.0 48.6 In January 2017, the Company entered into an At Market Issuance Sales Agreement (“January 2017 Sales Agreement”), which allowed it to issue and sell up to $ 75 50.9 63.4 1.27 6.8 10.3 During the first quarter of 2016, in connection with the Company’s issuance of the Notes, the Company also entered into privately negotiated capped call transactions as discussed in Note 9. The cost of the capped call transactions and associated expenses totaling $ 38.5 In March 2015, the Company completed a public offering of 27,758,620 3,620,689 7.25 11.6 190 In 2015, the Company sold 1.4 10.63 14.6

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Stock-Based Compensation [Abstract]
Stock-Based Compensation	Note 11 – Stock-Based Compensation Stock Options The 2015 Stock Incentive Plan, as amended, (“2015 Plan”) was approved at the Company’s annual meeting of stockholders in June 2015. Under the 2015 Plan, equity awards may be granted to officers, directors, employees and consultants of and advisors to the Company and any present or future subsidiary. The 2015 Plan authorizes the issuance of up to 36,000,000 The Amended and Restated 2005 Stock Incentive Plan (“2005 Plan”) expired in February 2015 and no new awards may be made under such plan, although awards will continue to be outstanding in accordance with their terms. The 2015 Plan permits and the 2005 Plan permitted the grant of stock options (including incentive stock options), restricted stock, stock appreciation rights and restricted stock units. In addition, under the 2015 Plan, unrestricted stock, stock units and performance awards may be granted. Stock options and stock appreciation rights generally have a maximum term of 10 100 Stock Options Awards 2015 Plan 2005 Plan Stock Weighted- Stock Weighted- Outstanding at January 1, 2017 25,104,603 $ 4.87 14,128,129 $ 3.30 Granted 12,411,543 $ 1.37 — $ — Exercised — $ — (115,000) $ 1.25 Canceled (3,840,426) $ 4.65 (1,194,200) $ 3.92 Outstanding at December 31, 2017 33,675,720 $ 3.61 12,818,929 $ 3.26 Shares exercisable at December 31, 2017 8,550,717 $ 5.87 11,659,554 $ 3.04 Shares available for grant at December 31, 2017 2,279,280 2017 2016 2015 Weighted average fair value of options granted $1.06 $1.88 $4.38 Risk-free interest rate 1.61%-2.34% 0.97%-1.78% 1.19%-2.13% Dividend yield 0% 0% 0% Volatility 88.91%-114.10% 57.86%-108.88% 53.58%-68.39% Expected term (in years) 4.14-7.46 4.22-7.28 3.98-7.34 Expected forfeiture rate(1) N/A 0%-16.33% 0%-16.33% (1) See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017. The Company used the Monte Carlo simulation model to determine the fair value of its 1.7 99.11 1.74 5.62 0 0.74 0.92 1.35 3.50 The total aggregate intrinsic value and weighted-average remaining contractual term of stock options outstanding under the 2015 Plan and 2005 Plan as of December 31, 2017 was $ 0.1 7.7 0.1 6.2 0.1 2.4 9.7 Employee Stock Purchase Plan In 2013, the Company adopted an Employee Stock Purchase Plan (the “ESPP”), which currently authorizes an aggregate of 3,450,000 shares of common stock to be purchased, and the aggregate amount of shares will continue to increase 5% on each anniversary of its adoption up to a maximum of 4,000,000 shares. The number of authorized shares and the maximum number of shares both include an increase of 1,000,000 shares approved at the Company’s 2016 annual meeting of stockholders. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate). 808,425 The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: 2017 2016 2015 Range of Black-Scholes fair values of ESPP shares granted $0.45-$5.47 $1.86-$4.76 $1.06-$3.38 Risk-free interest rate 0.45%-1.13% 0.22%-0.61% 0.05%-0.35% Dividend yield 0% 0% 0% Volatility 45.98%-267.85% 43.03%-86.75% 40.79%-64.24% Expected term (in years) 0.5-2.0 0.5-2.0 0.5-2.0 Expected forfeiture rate(1) N/A 5% 5% (1) See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017. Restricted Stock Awards Number of Per Share Outstanding and Unvested at January 1, 2017 45,000 $ 4.99 Restricted stock granted — $ — Restricted stock vested (26,250) $ 4.99 Restricted stock forfeited — $ — Outstanding and Unvested at December 31, 2017 18,750 $ 4.99 Year Ended December 31, 2017 2016 2015 Research and development $ 11,750 $ 11,168 $ 6,771 General and administrative 8,059 7,992 6,660 Total stock-based compensation expense $ 19,809 $ 19,160 $ 13,431 As of December 31, 2017, there was approximately $ 36 1.6

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2017
Pension and Other Postretirement Benefit Contributions [Abstract]
Employee Benefits	Note 12 – Employee Benefits The Company maintains a defined contribution 401(k) retirement plan, pursuant to which employees may elect to contribute up to 100 The Company matches 100 3 50 2 4 1.5 1.5 0.8 The Company’s foreign subsidiary has a pension plan under local tax and labor laws and is obligated to make contributions to this plan. Contributions and other expenses related to this plan were $ 0.5

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Note 13 – Income Taxes 2017 2016 2015 Domestic $ (173,749) $ (273,134) $ (150,227) Foreign (10,020) (6,832) (6,710) Total net loss $ (183,769) $ (279,966) $ (156,937) As a result of current and historical losses, there is no income tax provision for the years ended December 31, 2017, 2016 and 2015. 2017 2016 Deferred tax assets: Federal and State net operating loss carryforward $ 240,550 $ 286,619 Foreign net operating loss carryforward 11,577 9,011 Research tax credits 27,571 23,260 Deferred revenue 668 10,121 Original discount interest 7,167 12,445 Other 16,496 17,981 Total deferred tax assets 304,029 359,437 Valuation allowance (299,862) (354,530) Net deferred tax assets $ 4,167 $ 4,907 Deferred tax liabilities: Intangibles (1,789) (2,090) Other (2,378) (2,817) Total deferred tax liabilities (4,167) (4,907) Net deferred tax assets $ — $ — At December 31, 2017, the Company has provided provisional accounting for the tax effects of enactment of the Act. The Company re-measured certain of its U.S. deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future. As a result, the Company’s U.S. deferred tax balances at December 31, 2017 were revalued at the newly enacted tax rate, decreasing the net deferred tax asset (before valuation allowance) by approximately $ 132 The valuation allowance decreased $54.7 million during the year ended December 31, 2017 primarily due to the impact of the Act and was partially offset by the generation of net operating losses in 2017. The valuation allowance increased by $ 117.7 The differences between the U.S. federal statutory tax rate and the Company’s effective tax rate are as follows: 2017 2016 2015 Statutory federal tax rate (34) % (34) % (34) % State income taxes, net of federal benefit (3) % (3) % (3) % Research and development and other tax credits (2) % (2) % (3) % Release of FIN 48 liability 0 % 0 % (2) % Other (1) % 2 % 1 % Change in tax rate 70 % 0 % 0 % Change in valuation allowance (30) % 37 % 41 % Income tax provision 0 % 0 % 0 % Realization of net deferred tax assets is dependent on the Company’s ability to generate future taxable income, which is uncertain. Accordingly, a full valuation allowance was recorded against these assets as of December 31, 2017 and 2016 as management believes it is more likely than not that the assets will not be realizable. Amount Federal and State net operating losses expiring through the year 2037 $ 974,463 Foreign net operating losses (no expiration) 52,621 Research tax credits expiring through the year 2037 27,477 Utilization of the net operating loss carryforwards and credits may be subject to an annual limitation due to prior ownership change of the Company. The Company does not expect such limitation, if any, to impact the use of the net operating losses and business tax credits. At December 31, 2017 and 2016, the Company did not have any unrecognized tax benefits. To the extent unrecognized tax benefits are ultimately recognized, it would affect the annual effective income tax rate unless otherwise offset by a corresponding change in the valuation allowance. The Company does not expect that the amounts of unrecognized tax benefits will change significantly within the next twelve months. The Company files income tax returns in the U.S. federal jurisdiction and in various states, as well as in Sweden. The Company had U.S. tax net operating losses and credit carryforwards that are subject to examination from 1998 through 2017. The statute extends for a number of years beyond the year in which the losses were generated for tax purposes. Since a portion of these carryforwards may be utilized in the future, many of these attribute carryforwards remain subject to examination. The returns in Sweden are subject to examination from 2010 through 2017. The Company’s policy is to recognize interest and penalties related to income tax matters in income tax expense. As of December 31, 2017 and 2016, the Company had no accruals for interest or penalties related to income tax matters.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 14 – Commitments and Contingencies Operating Leases The Company conducts its operations from leased facilities. The operating leases for these facilities have terms expiring through 2026, unless earlier terminated by the Company in 2023. The leases contain provisions for future rent increases. Also, the leases obligate the Company to pay building operating costs. The Company records a deferred rent liability to account for the funding under improvement allowances and to record rent expense on a straight-line basis for these operating leases. Year Operating 2018 $ 6,695 2019 6,693 2020 5,416 2021 5,398 2022 5,515 Thereafter 6,801 Total minimum lease payments $ 36,518 Total rent expenses approximated $ 8.4 7.0 4.2 After re-evaluating its real estate needs, the Company amended its lease for approximately 147,000 5.3 1 Contingencies In 2007, the Company entered into an agreement to license certain rights from Wyeth Holdings Corporation, a subsidiary of Pfizer Inc. (“Wyeth”). The Wyeth license is a non-exclusive, worldwide license to a family of patents and patent applications covering VLP technology for use in human vaccines in certain fields, with expected patent expiration in early 2022. The Wyeth license provides for the Company to make an upfront payment (previously made), ongoing annual license fees, sublicense payments, milestone payments on certain development and commercialization activities and royalties on any product sales. Except in certain circumstances in which the Company continuously markets multiple products in a country within the same vaccine program, the milestone payments are one-time only payments applicable to each related vaccine program. At present, CPLB’s recombinant trivalent seasonal VLP influenza vaccine (“CadiFlu”) is the only program to which the Wyeth license applies. The license may be terminated by Wyeth only for cause and may be terminated by the Company only after it has provided ninety (90) days’ notice that the Company has absolutely and finally ceased activity, including through any affiliate or sublicense, related to the manufacturing, development, marketing or sale of products covered by the license. In September 2015, the Company entered into an amendment to the license agreement with Wyeth. Among other things, the amendment restructured the $ 3 14 15 0.2 0.3 7.6

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Note 15 – Related Party Transactions Dr. Rajiv Modi, a director of the Company, is also the managing director of Cadila. The Company and Cadila formed a joint venture, CPLB (see Note 7). A subsidiary of Cadila owned 2.5 0.1 0.4 2.2 0.1 In July 2017, the Company entered into a consulting agreement with Dr. Sarah Frech, the spouse of Mr. Stanley C. Erck, the Company’s President, Chief Executive Officer and Interim Chief Financial Officer. Dr. Frech is a seasoned biotechnology executive with significant experience managing multiple clinical programs. Under the agreement, Dr. Frech provides clinical development and operations services related to the Company’s Phase 3 clinical trial of its RSV F Vaccine for infants via maternal immunization and other professional services. The agreement is scheduled to terminate in July 2018. In 2017, the Company incurred $ 0.2 0.1

Quarterly Financial Information

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	Note 16 – Quarterly Financial Information (Unaudited) Quarter Ended March 31 June 30 September 30 December 31 (in thousands, except per share data) 2017: Revenue $ 5,680 $ 6,732 $ 8,352 $ 10,412 Net loss $ (43,854) $ (44,465) $ (44,607) $ (50,843) Net loss per share $ (0.16) $ (0.16) $ (0.15) $ (0.16) Quarter Ended March 31 June 30 September 30 December 31 (in thousands, except per share data) 2016: Revenue $ 4,218 $ 2,505 $ 3,231 $ 5,399 Net loss $ (77,252) $ (79,351) $ (66,254) $ (57,109) Net loss per share $ (0.29) $ (0.29) $ (0.24) $ (0.21) The net loss per share was calculated for each three-month period on a stand-alone basis. As a result, the sum of the net loss per share for the four quarters may not equal the net loss per share for the respective twelve-month period.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of Novavax, Inc. and its wholly owned subsidiary, Novavax AB. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with accounting principles generally accepted in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents 2017 2016 Cash $ 10,482 $ 17,481 Money market funds 36,762 95,896 Asset-backed securities 16,007 19,000 Corporate debt securities 43,056 11,976 Cash and cash equivalents $ 106,307 $ 144,353 Cash equivalents are recorded at cost, which approximate fair value due to their short-term nature.
Marketable Securities	Marketable Securities Marketable securities consist of commercial paper, asset-backed securities and corporate notes. Classification of marketable securities between current and non-current is dependent upon the maturity date at the balance sheet date taking into consideration the Company’s ability and intent to hold the investment to maturity. Interest and dividend income is recorded when earned and included in investment income in the consolidated statements of operations. Premiums and discounts, if any, on marketable securities are amortized or accreted to maturity and included in investment income in the consolidated statements of operations. The specific identification method is used in computing realized gains and losses on the sale of the Company’s securities. The Company classifies its marketable securities with readily determinable fair values as “available-for-sale.” Investments in securities that are classified as available-for-sale are measured at fair market value in the consolidated balance sheets, and unrealized holding gains and losses on marketable securities are reported as a separate component of stockholders’ deficit until realized. Marketable securities are evaluated periodically to determine whether a decline in value is “other-than-temporary.” The term “other-than-temporary” is not intended to indicate a permanent decline in value. Rather, it means that the prospects for a near term recovery of value are not necessarily favorable, or that there is a lack of evidence to support fair values equal to, or greater than, the carrying value of the security. Management reviews criteria, such as the magnitude and duration of the decline, as well as the Company’s ability to hold the securities until market recovery, to predict whether the loss in value is other-than-temporary. If a decline in value is determined to be other-than-temporary, the value of the security is reduced and the impairment is recorded as other income (expense) in the consolidated statements of operations.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments, which possibly expose the Company to concentration of credit risk, consist primarily of cash and cash equivalents and marketable securities. The Company’s investment policy limits investments to certain types of instruments, including asset-backed securities, high-grade corporate debt securities and money market funds, places restrictions on maturities and concentrations in certain industries and requires the Company to maintain a certain level of liquidity. At times, the Company maintains cash balances in financial institutions, which may exceed federally insured limits. The Company has not experienced any losses relating to such accounts and believes it is not exposed to a significant credit risk on its cash and cash equivalents.
Fair Value Measurements	Fair Value Measurements The Company applies Accounting Standards Codification (“ASC”) Topic 820, Fair Value Measurements and Disclosures ASC 820 discusses valuation techniques, such as the market approach (comparable market prices), the income approach (present value of future income or cash flow) and the cost approach (cost to replace the service capacity of an asset or replacement cost). The statement utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The following is a brief description of those three levels: · Level 1: Observable inputs such as quoted prices (unadjusted) in active markets for identical assets or liabilities. · Level 2: Inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. · Level 3: Unobservable inputs that reflect the reporting entity’s own assumptions.
Restricted Cash	Restricted Cash The Company’s current and non-current restricted cash includes payments received under the Grant Agreement (see Note 7) and cash collateral accounts under letters of credit that serve as security deposits for certain facility leases. The Company will utilize the funds from the Grant Agreement as it incurs expenses for services performed under the agreement. At December 31, 2017 and 2016, the restricted cash balances (both current and non-current) consist of payments received under the Grant Agreement of $ 27.4 33.2 1.7
Property and Equipment	Property and Equipment Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Amortization of leasehold improvements is computed using the straight-line method over the shorter of the estimated useful lives of the improvements or the remaining term of the lease. Repairs and maintenance costs are expensed as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable based on the criteria for accounting for the impairment or disposal of long-lived assets under ASC Topic 360, Property, Plant and Equipment.
Goodwill	Goodwill Goodwill is subject to impairment tests annually or more frequently should indicators of impairment arise. The Company has determined that, because its only business is the development of recombinant vaccines, it operates as a single operating segment and has one reporting unit. The Company utilizes primarily the market approach and, if considered necessary, the income approach to determine if it has an impairment of its goodwill. The market approach is based on market value of invested capital. To ensure that the Company’s capital stock is the appropriate measurement of fair value, the Company considers factors such as its trading volume, diversity of investors and analyst coverage. If considered necessary, the income approach is used to corroborate the results of the market approach. Goodwill impairment may exist if the carrying value of the reporting unit exceeds its estimated fair value. If the carrying value of the reporting unit exceeds its fair value, step two of the impairment analysis is performed. In step two of the analysis, an impairment loss is recorded equal to the excess of the carrying value of the reporting unit’s goodwill over its implied fair value, should such a circumstance arise. At December 31, 2017 and 2016, the Company used the market approach to determine if the Company had an impairment of its goodwill. The fair value of the Company’s single reporting unit was substantially higher than its carrying value, resulting in no impairment to goodwill at December 31, 2017 and 2016.
Other Intangible Assets	Other Intangible Assets The Company’s intangible assets include proprietary adjuvant technology and collaboration agreements, which were measured at their estimated fair values as of their acquisition dates. Amortization expense for intangible assets is recorded on a straight-line basis over the expected useful lives of the assets, ranging from seven to 20
Equity Method Investment	Equity Method Investment The Company has an equity investment in CPL Biologicals Private Limited (“CPLB”). The Company accounts for this investment using the equity method (see Note 7). Under the equity method of accounting, investments are stated at initial cost and are adjusted for subsequent additional investments and the Company’s proportionate share of earnings or losses and distributions up to the amount initially invested or advanced.
Revenue Recognition	Revenue Recognition The Company performs research and development for U.S. Government agencies and on behalf of grantors and other collaborators under cost reimbursable and fixed price contracts, including license, grant and clinical development agreements. The Company recognizes revenue under research contracts when a contract has been executed, the contract price is fixed or determinable, delivery of services or products has occurred and collection of the contract price is reasonably assured. Payments received in advance of work performed are recorded as deferred revenue and losses on contracts, if any, are recognized in the period in which they become known. Under its Grant Agreement with BMGF (see Note 7), the Company is reimbursed for certain costs that support development activities, including the Company’s global Phase 3 clinical trial in pregnant women in their third trimester, product licensing efforts and efforts to obtain World Health Organization (“WHO”) prequalification of its RSV F Vaccine. Payments received under the Grant Agreement are recognized as revenue in the period in which such research and development activities are performed. The Company analyzes its grant agreements to determine whether the payments received should be recorded as revenue or as a reduction to research and development expenses. In reaching this determination, management considers a number of factors, including whether the Company is principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s core operations. Historically, payments received under grant agreements have been recognized as revenue since the Company acts as a principal in the arrangement and the activities are core to its operations. Under cost reimbursable contracts with U.S. Government agencies, the Company is reimbursed and recognizes revenue as allowable costs are incurred plus a portion of the fixed-fee earned. The Company considers fixed-fees under cost reimbursable contracts to be earned in proportion to the allowable costs incurred in performance of the work as compared to total estimated contract costs, with such costs incurred representing a reasonable measurement of the proportional performance of the work completed. Under its HHS BARDA contract (see Note 7), certain activities were pre-approved by HHS BARDA in order for their costs to be deemed allowable direct costs. Direct costs incurred under cost reimbursable contracts are recorded as research and development expenses. Payments to the Company under cost reimbursable contracts with agencies of the U.S. Government, such as the HHS BARDA contract, are provisional payments subject to adjustment upon audit by the government. When the final determination of the additional reimbursable costs for any year has been made, and such amount is known and collection of the amount is reasonably assured, revenue and billings will be adjusted accordingly. Revenue associated with upfront payments under arrangements is recognized over the contract term or when all obligations associated with the upfront payment have been satisfied.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation related to grants of stock options, restricted stock awards and purchases under its Employee Stock Purchase Plan (the “ESPP”) at fair value. The Company recognizes compensation expense related to such awards on a straight-line basis over the requisite service period (generally the vesting period) of the equity awards, which typically occurs ratably over periods ranging from six months to four years. Effective January 1, 2017, the Company accounts for forfeitures when they occur. See Note 11 for a further discussion on stock-based compensation. The expected term of stock options granted was based on the Company’s historical option exercise experience and post-vesting forfeiture experience using the historical expected term from the vesting date, whereas the expected term for purchases under the ESPP was based on the purchase periods included in the offering. The expected volatility was determined using historical volatilities based on stock prices over a look-back period corresponding to the expected term. The risk-free interest rate was determined using the yield available for zero-coupon U.S. Government issues with a remaining term equal to the expected term. The Company has never paid a dividend, and as such, the dividend yield is zero, and the Company does not intend to pay dividends in the foreseeable future. Restricted stock awards have been recorded as compensation expense over the expected vesting period based on the fair value at the award date using the straight-line method of amortization. The Company accounts for share-based awards issued to non-employees by determining the fair value of equity awards given as consideration for services rendered to be recognized as compensation expense over the shorter of the vesting or service periods. In cases where an equity award is not fully vested, such equity award is revalued on each subsequent reporting date until vesting is complete with a cumulative catch-up adjustment recognized for any changes in its estimated fair value.
Research and Development Expenses	Research and Development Expenses Research and development expenses include salaries, stock-based compensation, laboratory supplies, consultants and subcontractors, including external contract research organizations (“CROs”), and other expenses associated with the Company’s process development, manufacturing, clinical, regulatory and quality assurance activities for its programs. In addition, related indirect costs such as, fringe benefits and overhead expenses, are also included in research and development expenses. Research and development activities are expensed as incurred. Accrued Research and Development Expenses The Company accrues research and development expenses, including clinical trial-related expenses, as the services are performed, which may include estimates of those expenses incurred, but not invoiced. The Company uses information provided by third-party service providers and CROs, invoices and internal estimates to determine the progress of work performed on the Company’s behalf. Assumptions based on clinical trial protocols, contracts and participant enrollment data are also developed to determine and analyze these estimates and accruals.
Income Taxes	Income Taxes The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes Tax benefits associated with uncertain tax positions are recognized in the period in which one of the following conditions is satisfied: (1) the more likely than not recognition threshold is satisfied; (2) the position is ultimately settled through negotiation or litigation; or (3) the statute of limitations for the taxing authority to examine and challenge the position has expired. Tax benefits associated with an uncertain tax position are reversed in the period in which the more likely than not recognition threshold is no longer satisfied. Interest and penalties related to income tax matters are recorded as income tax expense. At December 31, 2017 and 2016, the Company had no accruals for interest or penalties related to income tax matters. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was enacted into law, and the new legislation contains certain key tax provisions that affected the Company, including a reduction of the corporate income tax rate from 35 21 Income Tax Accounting Implications of the Tax Cuts and Jobs Act
Net Loss per Share	Net Loss per Share Net loss per share is computed using the weighted average number of shares of common stock outstanding. At December 31, 2017, 2016 and 2015, the Company had outstanding stock options and unvested restricted stock awards totaling 46,513,399 39,277,732 23,832,545 47,716,900
Foreign Currency	Foreign Currency The accompanying consolidated financial statements are presented in U.S. dollars. The functional currency of Novavax AB, which is located in Sweden, is the local currency (Swedish Krona). The translation of assets and liabilities of Novavax AB to U.S. dollars is made at the exchange rate in effect at the consolidated balance sheet date, while equity accounts are translated at historical rates. The translation of the statement of operations data is made at the average exchange rate in effect for the period. The translation of operating cash flow data is made at the average exchange rate in effect for the period, and investing and financing cash flow data is translated at the exchange rate in effect at the date of the underlying transaction. Translation gains and losses are recognized as a component of accumulated other comprehensive loss in the accompanying consolidated balance sheets. The foreign currency translation adjustment balance included in accumulated other comprehensive loss was $ 8.6 11.8
Segment Information	Segment Information The Company manages its business as one operating segment: the development of recombinant vaccines. The Company does not operate separate lines of business with respect to its vaccine candidates. Accordingly, the Company does not have separately reportable segments as defined by ASC Topic 280, Segment Reporting
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-09, Compensation - Stock Compensation (Topic 718) 0.6 Not Yet Adopted In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350)

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Schedule of Cash and Equivalents	Cash and cash equivalents consist of highly liquid investments with maturities of three months or less from the date of purchase. Cash and cash equivalents consist of the following at December 31 (in thousands): 2017 2016 Cash $ 10,482 $ 17,481 Money market funds 36,762 95,896 Asset-backed securities 16,007 19,000 Corporate debt securities 43,056 11,976 Cash and cash equivalents $ 106,307 $ 144,353

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements [Abstract]
Fair Value Hierarchy	The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis (in thousands): Fair Value at December 31, 2017 Fair Value at December 31, 2016 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Money market funds(1) $ 36,762 $ — $ — $ 95,896 $ — $ — Asset-backed securities(2) — 29,750 — — 42,632 — Corporate debt securities(3) — 80,309 — — 79,470 — Total cash equivalents and marketable securities $ 36,762 $ 110,059 $ — $ 95,896 $ 122,102 $ — Liabilities Convertible notes payable $ — $ 152,396 $ — $ — $ 141,989 $ — (1) Classified as cash and cash equivalents as of December 31, 2017 and 2016, respectively (see Note 3). (2) Includes $ 16,007 19,000 (3) Includes $ 43,056 11,976

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments [Abstract]
Investments Classified as Available-For-Sale	Marketable securities classified as available-for-sale as of December 31, 2017 and 2016 were comprised of (in thousands): December 31, 2017 December 31, 2016 Amortized Gross Gross Fair Value Amortized Gross Gross Fair Asset-backed securities $ 13,748 $ — $ (5) $ 13,743 $ 23,636 $ — $ (4) $ 23,632 Corporate debt securities 37,265 — (12) 37,253 67,457 43 (6) 67,494 Total $ 51,013 $ — $ (17) $ 50,996 $ 91,093 $ 43 $ (10) $ 91,126

Goodwill and Other Intangible29

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Other Intangible Assets [Abstract]
Schedule of Goodwill	The changes in the carrying amounts of goodwill for the years ended December 31, 2017 and 2016 were as follows (in thousands): Year Ended 2017 2016 Beginning balance $ 51,673 $ 53,065 Currency translation 1,890 (1,392) Ending balance $ 53,563 $ 51,673
Schedule of Identifiable Intangible Assets	Purchased intangible assets consisted of the following as of December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Gross Accumulated Intangible Gross Accumulated Intangible Finite-lived intangible assets: Proprietary adjuvant technology $ 9,086 $ (2,006) $ 7,080 $ 8,222 $ (1,404) $ 6,818 Collaboration agreements 4,103 (3,310) 793 3,713 (1,306) 2,407 Total identifiable intangible assets $ 13,189 $ (5,316) $ 7,873 $ 11,935 $ (2,710) $ 9,225
Schedule of Estimated Amortization Expense	Estimated amortization expense for existing intangible assets for each of the five succeeding years ending December 31, is as follows (in thousands): Year Amount 2018 $ 761 2019 761 2020 633 2021 454 2022 454

Other Financial Information (Ta

Other Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Other Financial Information [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following at December 31 (in thousands): 2017 2016 Laboratory supplies $ 13,085 $ 15,736 Other prepaid expenses and other current assets 4,689 6,301 Prepaid expenses and other current assets $ 17,774 $ 22,037
Property and Equipment, Net	Property and equipment is comprised of the following at December 31 (in thousands): 2017 2016 Machinery and equipment $ 35,409 $ 32,596 Leasehold improvements 23,664 22,642 Computer hardware 5,091 4,285 Construction in progress 1,129 2,938 65,293 62,461 Less — accumulated depreciation (29,306) (22,277) Property and equipment, net $ 35,987 $ 40,184
Accrued Expenses	Accrued expenses consist of the following at December 31 (in thousands): 2017 2016 Employee benefits and compensation $ 11,186 $ 7,300 Research and development accruals 17,542 15,744 Other accrued expenses 882 1,464 Accrued expenses $ 29,610 $ 24,508

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Notes Payable	Total convertible notes payable consisted of the following at (in thousands): December 31, December 31, Principal amount of Notes $ 325,000 $ 325,000 Unamortized debt issuance costs (7,237) (8,661) Total convertible notes payable $ 317,763 $ 316,339
Interest Expense	Interest expense incurred in connection with the Notes consisted of the following for the years ended December 31 (in thousands): 2017 2016 Coupon interest $ 12,188 $ 11,240 Amortization of debt issuance costs 1,424 1,305 Total interest expense on Notes $ 13,612 $ 12,545

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Summary of Option Activity	The following is a summary of option activity under the 2015 Plan and the 2005 Plan for the year ended December 31, 2017: 2015 Plan 2005 Plan Stock Weighted- Stock Weighted- Outstanding at January 1, 2017 25,104,603 $ 4.87 14,128,129 $ 3.30 Granted 12,411,543 $ 1.37 — $ — Exercised — $ — (115,000) $ 1.25 Canceled (3,840,426) $ 4.65 (1,194,200) $ 3.92 Outstanding at December 31, 2017 33,675,720 $ 3.61 12,818,929 $ 3.26 Shares exercisable at December 31, 2017 8,550,717 $ 5.87 11,659,554 $ 3.04 Shares available for grant at December 31, 2017 2,279,280
Assumptions used to Estimate Grant Date Fair Value of Stock Options granted using Black-Scholes Option-Pricing Model	The fair value of stock options granted under the 2015 Plan and 2005 Plan was estimated at the date of grant or the date upon which the 2015 Plan was approved by the Company’s stockholders for stock options granted prior to that time using the Black-Scholes option-pricing model with the following assumptions: 2017 2016 2015 Weighted average fair value of options granted $1.06 $1.88 $4.38 Risk-free interest rate 1.61%-2.34% 0.97%-1.78% 1.19%-2.13% Dividend yield 0% 0% 0% Volatility 88.91%-114.10% 57.86%-108.88% 53.58%-68.39% Expected term (in years) 4.14-7.46 4.22-7.28 3.98-7.34 Expected forfeiture rate(1) N/A 0%-16.33% 0%-16.33% (1) See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017.
Summary of Restricted Stock Awards Activity	The following is a summary of restricted stock awards activity for the year ended December 31, 2017: Number of Per Share Outstanding and Unvested at January 1, 2017 45,000 $ 4.99 Restricted stock granted — $ — Restricted stock vested (26,250) $ 4.99 Restricted stock forfeited — $ — Outstanding and Unvested at December 31, 2017 18,750 $ 4.99
Stock-Based Compensation Expense	The Company recorded stock-based compensation expense for awards issued under the above mentioned plans in the consolidated statements of operations as follows (in thousands): Year Ended December 31, 2017 2016 2015 Research and development $ 11,750 $ 11,168 $ 6,771 General and administrative 8,059 7,992 6,660 Total stock-based compensation expense $ 19,809 $ 19,160 $ 13,431
Employee Stock Purchase Plan [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Assumptions used to Estimate Grant Date Fair Value of Stock Options granted using Black-Scholes Option-Pricing Model	The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: 2017 2016 2015 Range of Black-Scholes fair values of ESPP shares granted $0.45-$5.47 $1.86-$4.76 $1.06-$3.38 Risk-free interest rate 0.45%-1.13% 0.22%-0.61% 0.05%-0.35% Dividend yield 0% 0% 0% Volatility 45.98%-267.85% 43.03%-86.75% 40.79%-64.24% Expected term (in years) 0.5-2.0 0.5-2.0 0.5-2.0 Expected forfeiture rate(1) N/A 5% 5% (1) See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Company’s loss from operations before income tax expense by jurisdiction	The Company’s loss from operations before income tax expense by jurisdiction for the years ended December 31 are as follows (in thousands): 2017 2016 2015 Domestic $ (173,749) $ (273,134) $ (150,227) Foreign (10,020) (6,832) (6,710) Total net loss $ (183,769) $ (279,966) $ (156,937)
Deferred Tax Assets (Liabilities)	Deferred tax assets (liabilities) consist of the following at December 31 (in thousands): 2017 2016 Deferred tax assets: Federal and State net operating loss carryforward $ 240,550 $ 286,619 Foreign net operating loss carryforward 11,577 9,011 Research tax credits 27,571 23,260 Deferred revenue 668 10,121 Original discount interest 7,167 12,445 Other 16,496 17,981 Total deferred tax assets 304,029 359,437 Valuation allowance (299,862) (354,530) Net deferred tax assets $ 4,167 $ 4,907 Deferred tax liabilities: Intangibles (1,789) (2,090) Other (2,378) (2,817) Total deferred tax liabilities (4,167) (4,907) Net deferred tax assets $ — $ —
Tax Rate Differences	The differences between the U.S. federal statutory tax rate and the Company’s effective tax rate are as follows: 2017 2016 2015 Statutory federal tax rate (34) % (34) % (34) % State income taxes, net of federal benefit (3) % (3) % (3) % Research and development and other tax credits (2) % (2) % (3) % Release of FIN 48 liability 0 % 0 % (2) % Other (1) % 2 % 1 % Change in tax rate 70 % 0 % 0 % Change in valuation allowance (30) % 37 % 41 % Income tax provision 0 % 0 % 0 %
Tax Return Reported Federal Net Operating Losses and Tax Credits Available	As of December 31, 2017, the Company had net operating losses and research tax credits available as follows (in thousands): Amount Federal and State net operating losses expiring through the year 2037 $ 974,463 Foreign net operating losses (no expiration) 52,621 Research tax credits expiring through the year 2037 27,477

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Rental Commitments Under Operating Leases	Future minimum rental commitments under non-cancelable leases as of December 31, 2017 (excluding commitments for the Clopper Road Lease as described below as this lease was terminated in January 2018) are as follows (in thousands): Year Operating 2018 $ 6,695 2019 6,693 2020 5,416 2021 5,398 2022 5,515 Thereafter 6,801 Total minimum lease payments $ 36,518

Quarterly Financial Informati35

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Information	The Company’s unaudited quarterly information for the years ended December 31, 2017 and 2016 is as follows: Quarter Ended March 31 June 30 September 30 December 31 (in thousands, except per share data) 2017: Revenue $ 5,680 $ 6,732 $ 8,352 $ 10,412 Net loss $ (43,854) $ (44,465) $ (44,607) $ (50,843) Net loss per share $ (0.16) $ (0.16) $ (0.15) $ (0.16) Quarter Ended March 31 June 30 September 30 December 31 (in thousands, except per share data) 2016: Revenue $ 4,218 $ 2,505 $ 3,231 $ 5,399 Net loss $ (77,252) $ (79,351) $ (66,254) $ (57,109) Net loss per share $ (0.29) $ (0.29) $ (0.24) $ (0.21)

Summary of Significant Accoun36

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 02, 2017
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share		46,513,399	39,277,732	23,832,545
Foreign currency translation adjustment		$ 8,600	$ 11,800
Restricted Cash and Cash Equivalents		$ 28,234	$ 30,314
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		34.00%	34.00%	34.00%
Accounting Standards Update 2016-09 [Member]
Summary of Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					$ 600
Security Deposit [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents		$ 1,700	$ 1,700
Grant Agreement [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents		$ 27,400	$ 33,200
Convertible Debt Securities [Member]
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share		47,716,900	47,716,900
Tax Act [Member]
Summary of Significant Accounting Policies [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		20 years
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%
Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 years

Summary of Significant Accoun37

Summary of Significant Accounting Policies (Cash and Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 106,307	$ 144,353	$ 93,108	$ 32,335
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	10,482	17,481
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	36,762	95,896
Asset-backed Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	16,007	19,000
Corporate debt securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 43,056	$ 11,976

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	$ 106,307	$ 144,353	$ 93,108	$ 32,335
Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	16,007	19,000
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	$ 43,056	$ 11,976

Fair Value Measurements (Fair v

Fair Value Measurements (Fair value hierarchy for its financial assets and liabilities) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Level 1 [Member]
Assets
Total assets		$ 36,762	$ 95,896
Liabilities
Convertible notes payable		0	0
Level 1 [Member] | Money market funds [Member]
Assets
Total assets	[1]	36,762	95,896
Level 1 [Member] | Asset-backed securities [Member]
Assets
Total assets	[2]	0	0
Level 1 [Member] | Corporate Debt Securities [Member]
Assets
Total assets	[3]	0	0
Level 2 [Member]
Assets
Total assets		110,059	122,102
Liabilities
Convertible notes payable		152,396	141,989
Level 2 [Member] | Money market funds [Member]
Assets
Total assets	[1]	0	0
Level 2 [Member] | Asset-backed securities [Member]
Assets
Total assets	[2]	29,750	42,632
Level 2 [Member] | Corporate Debt Securities [Member]
Assets
Total assets	[3]	80,309	79,470
Level 3 [Member]
Assets
Total assets		0	0
Liabilities
Convertible notes payable		0	0
Level 3 [Member] | Money market funds [Member]
Assets
Total assets	[1]	0	0
Level 3 [Member] | Asset-backed securities [Member]
Assets
Total assets	[2]	0	0
Level 3 [Member] | Corporate Debt Securities [Member]
Assets
Total assets	[3]	$ 0	$ 0
[1]	Classified as cash and cash equivalents as of December 31, 2017 and 2016, respectively (see Note 3).
[2]	Includes $16,007 and $19,000 classified as cash and cash equivalents as of December 31, 2017 and 2016, respectively (see Note 3).
[3]	Includes $43,056 and $11,976 classified as cash and cash equivalents as of December 31, 2017 and 2016, respectively (see Note 3).

Marketable Securities (Narrativ

Marketable Securities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Number	Dec. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-For-Sale Securities Number of Securities Owned | Number	19
Available-For-Sale Securities Number Of Securities Owned Unrealized Losses | Number	18
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $	$ 17	$ 10
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $	$ 100

Marketable Securities (Marketab

Marketable Securities (Marketable securities classified as available-for-sale) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 51,013	$ 91,093
Gross Unrealized Gains	0	43
Gross Unrealized Losses	(17)	(10)
Fair Value	50,996	91,126
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,748	23,636
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(4)
Fair Value	13,743	23,632
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,265	67,457
Gross Unrealized Gains	0	43
Gross Unrealized Losses	(12)	(6)
Fair Value	$ 37,253	$ 67,494

Goodwill and Other Intangible42

Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 2.2	$ 0.8	$ 0.9

Goodwill and Other Intangible43

Goodwill and Other Intangible Assets (Schedule of Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Beginning balance	$ 51,673	$ 53,065
Currency translation	1,890	(1,392)
Ending balance	$ 53,563	$ 51,673

Goodwill and Other Intangible44

Goodwill and Other Intangible Assets (Schedule of Identifiable Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 13,189	$ 11,935
Accumulated Amortization	(5,316)	(2,710)
Intangible Assets, Net	7,873	9,225
Collaboration agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,103	3,713
Accumulated Amortization	(3,310)	(1,306)
Intangible Assets, Net	793	2,407
Proprietary adjuvant technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	9,086	8,222
Accumulated Amortization	(2,006)	(1,404)
Intangible Assets, Net	$ 7,080	$ 6,818

Goodwill and Other Intangible45

Goodwill and Other Intangible Assets (Schedule of Estimated Amortization Expense) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Finite-Lived Intangible Assets [Line Items]
2,018	$ 761
2,019	761
2,020	633
2,021	454
2,022	$ 454

Grant, U.S. Government Contra46

Grant, U.S. Government Contract and Joint Venture (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended			28 Months Ended	83 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue			$ 0	$ 2,184	$ 33,344
Cadila [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Joint Venture Percentage Owned By Others			80.00%			80.00%	80.00%
HHS BARDA Contract [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Government Contract Receivable								$ 97,000
Increase in funding for recovery of additional costs under contract		$ 7,700
HHS BARDA Option for Additional Period [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Government Contract Receivable								$ 70,000
Bill Melinda Gates Foundation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Grant agreement	$ 89,100
CPL Biologicals Private Limited [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Ownership percentage			20.00%			20.00%	20.00%
Minimum [Member] | Bill Melinda Gates Foundation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue			$ 29,700
Maximum [Member] | HHS BARDA Contract [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue							$ 114,000
Maximum [Member] | Bill Melinda Gates Foundation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue						$ 42,000

Other Financial Information (Na

Other Financial Information (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Depreciation, Depletion and Amortization	$ 7.6	$ 7.7	$ 5.1

Other Financial Information (Pr

Other Financial Information (Prepaid Expenses and Other Current Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Laboratory supplies	$ 13,085	$ 15,736
Other prepaid expenses and other current assets	4,689	6,301
Prepaid expenses and other current assets	$ 17,774	$ 22,037

Other Financial Information (49

Other Financial Information (Property and Equipment, Net) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property and equipment	$ 65,293	$ 62,461
Less - accumulated depreciation and amortization	(29,306)	(22,277)
Property and equipment, net	35,987	40,184
Machinery and equipment [Member]
Property and equipment	35,409	32,596
Leasehold improvements [Member]
Property and equipment	23,664	22,642
Computer hardware [Member]
Property and equipment	5,091	4,285
Construction in progress [Member]
Property and equipment	$ 1,129	$ 2,938

Other Financial Information (Ac

Other Financial Information (Accrued Expenses) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Employee benefits and compensation	$ 11,186	$ 7,300
Research and development accruals	17,542	15,744
Other accrued expenses	882	1,464
Accrued expenses	$ 29,610	$ 24,508

Long-Term Debt (Narrative) (Det

Long-Term Debt (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jan. 25, 2016
Debt Instrument [Line Items]
Aggregate principal amount of notes issued	$ 325,000	$ 325,000	$ 325,000
Payment for capped call transactions	38,500
Debt Cap Price				9.73
Net proceeds received	315,000
Sale of Stock, Price Per Share				$ 5.56
Debt Issuance Costs	10,000
Capped Call Transactions Expenses	$ 900
Capped Call Transactions [Member]
Debt Instrument [Line Items]
Conversion Premium, Percentage				75.00%
Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Terms of Conversion Feature		In addition, the holders of the Notes may require the Company to repurchase the Notes at par value plus accrued and unpaid interest following the occurrence of a Fundamental Change (as described in the Indenture). If a holder of the Notes converts upon a Make-Whole Adjustment Event (as described in the Indenture), they may be eligible to receive a make-whole premium through an increase to the conversion rate up to a maximum of 179.8561 shares per $1,000 principal amount of Notes (subject to other adjustments as described in the Indenture).
Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Terms of Conversion Feature		The Notes are not redeemable prior to maturity and are convertible into shares ofthe Companyscommon stock. The Notes are initially convertible into approximately 47,716,900 shares of the Companys common stock based on the initial conversion rate of 146.8213 shares of the Companys common stock per$1,000principal amount of the Notes.
Unsecured Debt [Member]
Debt Instrument [Line Items]
Convertible Notes Payable, Maturity Date		Feb. 1, 2023
Conversion Premium, Percentage				22.50%
Annual Interest Rate of Notes (as a percent)		3.75%
Debt Instrument, Convertible, Conversion Price				$ 6.81

Long-Term Debt (Notes Payable)

Long-Term Debt (Notes Payable) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Principal amount of Notes	$ 325,000	$ 325,000	$ 325,000
Unamortized debt issuance costs	(7,237)	(8,661)
Total convertible notes payable	$ 317,763	$ 316,339

Long-Term Debt (Interest Expens

Long-Term Debt (Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Coupon interest	$ 12,188	$ 11,240
Amortization of debt issuance costs	1,424	1,305	$ 0
Total interest expense on Notes	$ 13,612	$ 12,545

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		2 Months Ended	3 Months Ended	12 Months Ended
	Jan. 17, 2018	Mar. 31, 2015	Mar. 09, 2018	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2015	Jan. 31, 2017	Jan. 25, 2016
Subsidiary, Sale of Stock [Line Items]
Sales per share price range								$ 5.56
Proceeds from shares sold					$ 63,425	$ 204,275
Convertible Debt [Member]
Subsidiary, Sale of Stock [Line Items]
Adjustments to Additional Paid IN capital, Cost and Expenses on Derivative Transaction				$ 38,500
Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range		$ 7.25
Shares sold		27,758,620
Common stock issued upon exercise in full over-allotment granted		3,620,689
Proceeds from shares sold		$ 190,000
Offering costs		$ 11,600
2012 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range						$ 10.63
Shares sold						1,400,000
Proceeds from shares sold						$ 14,600
December 2017 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value					$ 75,000
December 2017 Sales Agreement [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold			12,700,000
Proceeds from shares sold			$ 26,000
Shelf Registration Statement, Remaining Authorized Stock Issuance,Value			$ 48,600
January 2017 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Sales per share price range					$ 1.27
Shares sold					50,900,000
Proceeds from shares sold					$ 63,400
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value							$ 75,000
January 2017 Sales Agreement [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold	6,800,000
Proceeds from shares sold	$ 10,300

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options exercised		$ 0.1	$ 2.4	$ 9.7
Unrecognized compensation expense		$ 36
Unrecognized compensation expense, recognition period		1 year 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 1.06	$ 1.88	$ 4.38
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		0.00%	0.00%	0.00%
Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			1,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate			1.74%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate			99.11%
Share based Compensation Arrangement by Share based Payment Award Fair Value Assumptions Expected Forfeiture Rate			5.62%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate			0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based Compensation Arrangement by Share based Payment Award Fair Value Assumptions Expected Forfeiture Rate	[1]		16.33%	16.33%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term		7 years 5 months 16 days	7 years 3 months 11 days	7 years 4 months 2 days
Maximum [Member] | Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 0.92
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term		3 years 6 months
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based Compensation Arrangement by Share based Payment Award Fair Value Assumptions Expected Forfeiture Rate	[1]		0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term		4 years 1 month 20 days	4 years 2 months 19 days	3 years 11 months 23 days
Minimum [Member] | Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 0.74
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term		1 year 4 months 6 days
2005 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of options		10 years
Minimum grant price, percent of common stock fair value		100.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		0
2005 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		4 years
2005 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		6 months
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		808,425
Employee Stock Ownership Plan (ESOP), Plan Description		the Company adopted an Employee Stock Purchase Plan (the ESPP), which currently authorizes an aggregate of 3,450,000 shares of common stock to be purchased, and the aggregate amount of shares will continue to increase 5% on each anniversary of its adoption up to a maximum of 4,000,000 shares. The number of authorized shares and the maximum number of shares both include an increase of 1,000,000 shares approved at the Companys 2016 annual meeting of stockholders. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate).
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		36,000,000
Aggregate intrinsic value of stock options outstanding		$ 0.1
Weighted-average remaining contractual term of stock options outstanding		7 years 8 months 12 days
Aggregate intrinsic value of stock options exercisable		$ 0.1
Weighted-average remaining contractual term of stock options exercisable		6 years 2 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		12,411,543
[1]	See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017.

Stock-Based Compensation (Summa

Stock-Based Compensation (Summary of Option Activity) (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
2005 Plan [Member]
Stock Options
Outstanding at January 1, 2017	14,128,129
Granted	0
Exercised	(115,000)
Canceled	(1,194,200)
Outstanding at December 31, 2017	12,818,929
Shares exercisable at December 31, 2017	11,659,554
Weighted-Average Exercise Price
Outstanding at January 1, 2017 | $ / shares	$ 3.3
Granted | $ / shares	0
Exercised | $ / shares	1.25
Canceled | $ / shares	3.92
Outstanding at December 31, 2017 | $ / shares	3.26
Shares exercisable at December 31, 2017 | $ / shares	$ 3.04
2015 Plan [Member]
Stock Options
Outstanding at January 1, 2017	25,104,603
Granted	12,411,543
Exercised	0
Canceled	(3,840,426)
Outstanding at December 31, 2017	33,675,720
Shares exercisable at December 31, 2017	8,550,717
Shares available for grant at December 31, 2017	2,279,280
Weighted-Average Exercise Price
Outstanding at January 1, 2017 | $ / shares	$ 4.87
Granted | $ / shares	1.37
Exercised | $ / shares	0
Canceled | $ / shares	4.65
Outstanding at December 31, 2017 | $ / shares	3.61
Shares exercisable at December 31, 2017 | $ / shares	$ 5.87

Stock-Based Compensation (Assum

Stock-Based Compensation (Assumptions Used in Estimation of Fair Value of Stock) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted		$ 1.06	$ 1.88	$ 4.38
Risk-free interest rate, minimum		1.61%	0.97%	1.19%
Risk-free interest rate, maximum		2.34%	1.78%	2.13%
Dividend yield		0.00%	0.00%	0.00%
Volatility, minimum		88.91%	57.86%	53.58%
Volatility, maximum		114.10%	108.88%	68.39%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum		0.45%	0.22%	0.05%
Risk-free interest rate, maximum		1.13%	0.61%	0.35%
Dividend yield		0.00%	0.00%	0.00%
Volatility, minimum		45.98%	43.03%	40.79%
Volatility, maximum		267.85%	86.75%	64.24%
Expected forfeiture rate	[1]		5.00%	5.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		4 years 1 month 20 days	4 years 2 months 19 days	3 years 11 months 23 days
Expected forfeiture rate	[1]		0.00%	0.00%
Minimum [Member] | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted		$ 0.45	$ 1.86	$ 1.06
Expected term (in years)		6 months	6 months	6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		7 years 5 months 16 days	7 years 3 months 11 days	7 years 4 months 2 days
Expected forfeiture rate	[1]		16.33%	16.33%
Maximum [Member] | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted		$ 5.47	$ 4.76	$ 3.38
Expected term (in years)		2 years	2 years	2 years
[1]	See Note 3 regarding the Company’s adoption of ASU 2016-09 in 2017.

Stock-Based Compensation (Sum58

Stock-Based Compensation (Summary of Restricted Stock Awards Activity) (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Number of shares
Outstanding and Unvested at January 1, 2017 | shares	45,000
Restricted stock granted | shares	0
Restricted stock vested | shares	(26,250)
Restricted stock forfeited | shares	0
Outstanding and Unvested at December 31, 2017 | shares	18,750
Per Share Weighted-Average Grant-Date Fair Value
Outstanding and Unvested at January 1, 2017 | $ / shares	$ 4.99
Restricted stock granted | $ / shares	0
Restricted stock vested | $ / shares	4.99
Restricted stock forfeited | $ / shares	0
Outstanding and Unvested at December 31, 2017 | $ / shares	$ 4.99

Stock-Based Compensation (Stock

Stock-Based Compensation (Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 19,809	$ 19,160	$ 13,431
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	11,750	11,168	6,771
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 8,059	$ 7,992	$ 6,660

Employee Benefits (Narrative) (

Employee Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Maximum contribution percentage of compensation	100.00%
Contributions to employee benefits plan	$ 1.5	$ 1.5	$ 0.8
Contributions and other expenses related to foreign subsidiary	$ 0.5	$ 0.5	$ 0.5
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	4.00%
Next 2% Of Participants Deferral [Member]
Employer match percentage	50.00%
Percentage of employee deferral eligible for employer matching contribution	2.00%
First 3% Of Participants Deferral [Member]
Employer match percentage	100.00%
Percentage of employee deferral eligible for employer matching contribution	3.00%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ (54.7)	$ 117.7
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 132

Income Taxes (Loss from Operati

Income Taxes (Loss from Operations before Income Tax Expense by Jurisdiction) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss	$ (50,843)	$ (44,607)	$ (44,465)	$ (43,854)	$ (57,109)	$ (66,254)	$ (79,351)	$ (77,252)	$ (183,769)	$ (279,966)	$ (156,937)
Domestic Tax Authority [Member]
Net loss									(173,749)	(273,134)	(150,227)
Foreign Tax Authority [Member]
Net loss									$ (10,020)	$ (6,832)	$ (6,710)

Income Taxes (Deferred Tax Asse

Income Taxes (Deferred Tax Assets (Liabilities)) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and State net operating loss carryforward	$ 240,550	$ 286,619
Foreign net operating loss carryforward	11,577	9,011
Research tax credits	27,571	23,260
Deferred revenue	668	10,121
Original discount interest	7,167	12,445
Other	16,496	17,981
Total deferred tax assets	304,029	359,437
Valuation allowance	(299,862)	(354,530)
Net deferred tax assets	4,167	4,907
Deferred tax liabilities:
Intangibles	(1,789)	(2,090)
Other	(2,378)	(2,817)
Total deferred tax liabilities	(4,167)	(4,907)
Net deferred tax assets	$ 0	$ 0

Income Taxes (Tax Rates) (Detai

Income Taxes (Tax Rates) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory federal tax rate	(34.00%)	(34.00%)	(34.00%)
State income taxes, net of federal benefit	(3.00%)	(3.00%)	(3.00%)
Research and development and other tax credits	(2.00%)	(2.00%)	(3.00%)
Release of FIN 48 liability	0.00%	0.00%	(2.00%)
Other	(1.00%)	2.00%	1.00%
Change in tax rate	70.00%	0.00%	0.00%
Change in valuation allowance	(30.00%)	37.00%	41.00%
Income tax provision	0.00%	0.00%	0.00%

Income Taxes (Tax Return Report

Income Taxes (Tax Return Reported Federal Net Operating Losses and Tax Credits) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Federal [Member]
Net operating losses	$ 974,463
Foreign [Member]
Net operating losses	52,621
Research Tax Credit [Member]
Tax credit	$ 27,477
Net operating losses carried forward, expiration date	Dec. 31, 2037

Commitments and Contingencies66

Commitments and Contingencies (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)a	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)
Rent expense			$ 8.4	$ 7	$ 4.2
Accrued milestone payment associated with the first Phase 3 clinical trial						$ 3
Aggregate amount of payments made under license agreement			$ 7.6
Gaithersburg, Maryland [Member]
Rental Square Footage of Building | a			147,000
Gaithersburg, Maryland [Member] | Subsequent Event [Member]
Termination Fee	$ 5.3
Gaithersburg, Maryland [Member] | Scenario, Forecast [Member]
Total Termination Expenses		$ 1
Maximum [Member]
Increase In License Maintenance Fees			$ 0.3
Increase In Milestone Payment			15
Minimum [Member]
Increase In License Maintenance Fees			0.2
Increase In Milestone Payment			$ 14

Commitments and Contingencies67

Commitments and Contingencies (Future Minimum Rental Commitments) (Details) - Operating Leases [Member] $ in Thousands	Dec. 31, 2017USD ($)
Operating Leased Assets [Line Items]
2,018	$ 6,695
2,019	6,693
2,020	5,416
2,021	5,398
2,022	5,515
Thereafter	6,801
Total minimum lease payments	$ 36,518

Related Party Transactions (Nar

Related Party Transactions (Narrative) (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Due to Related Parties	$ 0	$ 100,000
Master services agreement expenses	$ 100,000	$ 400,000	$ 2,200,000
Subsidiary of Cadila [Member]
Related Party Transaction [Line Items]
Common Stock Shares Outstanding Related Party Transactions	2.5
Dr. Sarah Frech [Member]
Related Party Transaction [Line Items]
Consulting Expenses	$ 200,000
Due To Related Parties Unpaid for Services	$ 100,000

Quarterly Financial Informati69

Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Quarterly Financial Information [Line Items]
Revenue	$ 10,412	$ 8,352	$ 6,732	$ 5,680	$ 5,399	$ 3,231	$ 2,505	$ 4,218	$ 31,176	$ 15,353	$ 36,250
Net loss	$ (50,843)	$ (44,607)	$ (44,465)	$ (43,854)	$ (57,109)	$ (66,254)	$ (79,351)	$ (77,252)	$ (183,769)	$ (279,966)	$ (156,937)
Net loss per share	$ (0.16)	$ (0.15)	$ (0.16)	$ (0.16)	$ (0.21)	$ (0.24)	$ (0.29)	$ (0.29)	$ (0.63)	$ (1.03)	$ (0.6)