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Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Registrant Name	CHIMERIX INC
Entity Central Index Key	0001117480
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		51,072,798

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 19,705	$ 81,106
Short-term investments, available-for-sale	151,881	105,424
Accounts receivable	1,425	330
Prepaid expenses and other current assets	2,534	2,598
Total current assets	175,545	189,458
Property and equipment, net of accumulated depreciation	1,158	1,210
Operating lease right-of-use assets	1,232
Other long-term assets	53	46
Total assets	177,988	190,714
Current liabilities:
Accounts payable	2,492	4,691
Accrued liabilities	10,389	8,275
Total current liabilities	12,881	12,966
Lease-related obligations	800	144
Total liabilities	13,681	13,110
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized at March 31, 2019 and December 31, 2018; no shares issued and outstanding as of March 31, 2019 and December 31, 2018	0	0
Common stock, $0.001 par value, 200,000,000 shares authorized at March 31, 2019 and December 31, 2018; 51,023,842 and 50,735,279 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively	51	51
Additional paid-in capital	738,163	733,907
Accumulated other comprehensive gain (loss), net	48	(92)
Accumulated deficit	(573,955)	(556,262)
Total stockholders’ equity	164,307	177,604
Total liabilities and stockholders’ equity	$ 177,988	$ 190,714

Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Contract revenue	$ 2,356	$ 790
Operating expenses:
Research and development	13,515	14,359
General and administrative	7,686	6,738
Total operating expenses	21,201	21,097
Loss from operations	(18,845)	(20,307)
Other (expense) income:
Unrealized loss on equity investment	(8)	(134)
Interest income and other, net	1,160	615
Net loss	(17,693)	(19,826)
Other comprehensive loss:
Unrealized gain (loss) on debt investments, net	140	(103)
Comprehensive loss	$ (17,553)	$ (19,929)
Per share information:
Net loss, basic and diluted (in dollars per share)	$ (0.35)	$ (0.42)
Weighted-average shares outstanding, basic and diluted (in shares)	50,887,221	47,637,907

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	51,023,842	50,735,279
Common stock, shares outstanding (in shares)	51,023,842	50,735,279

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2017	$ 221,810	$ 47	$ 709,514	$ (963)	$ (486,788)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	3,392	1	3,391
Exercise of stock options	60		60
Employee stock purchase plan purchases	358		358
Comprehensive loss:
Unrealized gain (loss) on debt investments, net	(103)			(103)
Net loss	(19,826)				(19,826)
Comprehensive loss	(19,929)
Ending Balance at Mar. 31, 2018	205,691	48	713,323	(1,066)	(506,614)
Beginning Balance at Dec. 31, 2018	177,604	51	733,907	(92)	(556,262)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	4,073		4,073
Exercise of stock options	13		13
Employee stock purchase plan purchases	170		170
Comprehensive loss:
Unrealized gain (loss) on debt investments, net	140			140
Net loss	(17,693)				(17,693)
Comprehensive loss	(17,553)
Ending Balance at Mar. 31, 2019	$ 164,307	$ 51	$ 738,163	$ 48	$ (573,955)

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669619-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Section 45
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669625-108580

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4J
-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591551-111686

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3000-108585

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4K
-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591552-111686

+ Details

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (17,693)	$ (19,826)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	149	248
Amortization of discount/premium on investments	(595)	(73)
Share-based compensation	4,073	3,391
Unrealized loss on equity investment	8	134
Lease-related amortization	(16)	(11)
Changes in operating assets and liabilities:
Accounts receivable	(1,095)	1,256
Prepaid expenses and other assets	59	294
Accounts payable and accrued liabilities	(624)	(3,925)
Net cash used in operating activities	(15,734)	(18,512)
Cash flows from investing activities:
Purchases of property and equipment	(97)	(42)
Purchases of short-term investments	(69,680)	(1,989)
Purchases of long-term investments	0	(6,031)
Proceeds from sales of short-term investments	0	9,500
Proceeds from maturities of short-term investments	23,950	20,500
Net cash (used in) provided by investing activities	(45,827)	21,938
Cash flows from financing activities:
Proceeds from exercise of stock options	13	60
Proceeds from employee stock purchase plan	170	358
Payments of deferred offering costs	(23)	(280)
Net cash provided by financing activities	160	138
Net (decrease) increase in cash and cash equivalents	(61,401)	3,564
Cash and cash equivalents:
Beginning of period	81,106	18,548
End of period	$ 19,705	$ 22,112

The Business and Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

The Business and Summary of Significant Accounting Policies

Description of Business

Chimerix, Inc. (the Company) is a biopharmaceutical company committed to discovering, developing and commercializing medicines that improve outcomes for patients with life-threatening diseases. The Company was founded in 2000 based on the promise of its proprietary lipid conjugate technology to unlock the potential of some of the most broad-spectrum antivirals by enhancing their antiviral activity and safety profiles in convenient dosing regimens. The Company is developing brincidofovir for the treatment of smallpox.

Basis of Presentation

The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Company’s audited financial statements and notes thereto included in its Annual Report on Form 10-K for the year ended December 31, 2018. In the opinion of the Company’s management, all adjustments, consisting of normal recurring adjustments, necessary for a fair presentation of its financial position, operating results and cash flows for the periods presented have been included. Operating results for the three months ended March 31, 2019 are not necessarily indicative of the results that may be expected for the full year, for any other interim period or for any future year.

Fair Value of Financial Instruments

The carrying amounts of certain financial instruments, including accounts receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of such instruments.

For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements, in accordance with the fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates and are often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, fair value measurements cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the calculated current or future fair values. The Company utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures.

The Company groups assets and liabilities at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. The determination of where an asset or liability falls in the hierarchy requires significant judgment. These levels are:


•	Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.


•	Level 2 — Valuations based on quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and models for which all significant inputs are observable, either directly or indirectly.


•	Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.

At March 31, 2019, the Company had cash equivalents including money market accounts, and at December 31, 2018, the Company had cash equivalents including money market accounts and U.S. Treasury securities, whose value is based on using quoted market prices. At March 31, 2019 and December 31, 2018, the Company had short-term investments including U.S. Treasury securities, whose value is based on using quoted market prices. Accordingly, these securities are classified as Level 1.

At March 31, 2019 and December 31, 2018, the Company had short-term investments including stock of a U.S. corporation. The Company's investment in ContraVir Pharmaceuticals (ContraVir) common stock was categorized as a Level 1 asset and had a value based on ContraVir's common stock value at March 31, 2019 and December 31, 2018. For the three months ended March 31, 2019 and 2018, the Company recorded approximately $8,000 and $134,000, respectively, of unrealized loss related to the Company's investment in ContraVir common stock to unrealized loss on equity investment in the Consolidated Statements of Operations and Comprehensive Loss.

At March 31, 2019 and December 31, 2018, the Company had cash equivalents including commercial paper and corporate bonds, and short-term investments including commercial paper and corporate bonds. As quoted prices are not available for these securities, they are valued using independent pricing models or other model-based valuation techniques such as the present value of future cash flows, adjusted for the security’s credit rating, prepayment assumptions and other factors such as credit loss assumptions. Accordingly, these securities are classified as Level 2.

There was no material re-measurement to fair value of financial assets and liabilities that are not measured at fair value on a recurring basis. For additional information regarding the Company's investments, please refer to Note 2, "Investments."

Below are tables that present information about certain assets measured at fair value on a recurring basis (in thousands):



	Fair Value Measurements
	March 31, 2019
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	11,879	$	11,879	$	—	$	—
Commercial paper	2,699		—		2,699		—
Corporate bonds	2,000		—		2,000		—
Total cash equivalents	16,578		11,879		4,699		—
Short-term investments
U.S. treasury securities	42,960		42,960		—		—
Common stock of U.S. corporation	30		30		—		—
Commercial paper	54,182		—		54,182		—
Corporate bonds	54,709		—		54,709		—
Total short-term investments	151,881		42,990		108,891		—
Total assets	$	168,459	$	54,869	$	113,590	$	—

	Fair Value Measurements
	December 31, 2018
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	30,726	$	30,726	$	—	$	—
U.S. treasury securities	11,482		11,482		—		—
Commercial paper	29,677		—		29,677		—
Corporate bonds	4,008		—		4,008		—
Total cash equivalents	75,893		42,208		33,685		—
Short-term investments
U.S. treasury securities	12,589		12,589		—		—
Common stock of U.S. corporation	38		38		—		—
Commercial paper	60,114		—		60,114		—
Corporate bonds	32,683		—		32,683		—
Total short-term investments	105,424		12,627		92,797		—
Total assets	$	181,317	$	54,835	$	126,482	$	—

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Accrued research and development expenses	$	5,823	$	4,525
Accrued compensation	2,453		2,469
Other accrued liabilities	2,113		1,281
Total accrued liabilities	$	10,389	$	8,275

Revenue Recognition

Policy

The Company’s revenues generally consist of (i) contract revenue - revenue generated under federal contracts, and (ii) collaboration and licensing revenue - revenue related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenue is recognized in accordance with the criteria outlined in Accounting Standards Codification (ASC) 606 issued by the Financial Accounting Standards Board (FASB). Following this accounting pronouncement, a five-step approach is applied for recognizing revenue, including (1) identify the contract with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when, or as, the entity satisfies a performance obligation.

Biomedical Advanced Research and Development Authority (BARDA)

In February 2011, the Company entered into a contract with BARDA for the advanced development of brincidofovir as a medical countermeasure in the event of a smallpox release. Under the contract, the Company may receive up to $75.8 million in expense reimbursement and $5.3 million in fees over the performance of 1 base segment and 4 option segments. Exercise of each option segment is solely at the discretion of BARDA. Currently, option segments 1 through 3 have been exercised. The Company assessed the services in accordance with the authoritative guidance and concluded that there is a potential of 5 separate contracts (1 base segment and 4 option segments) within this agreement, each of which has a single performance obligation. The transaction price for each segment, based on the transaction price as defined in each segment contract, is allocated to the single performance obligation for each contract. The transaction price is recognized over time by measuring the progress toward complete satisfaction of the performance obligation. The progress toward complete satisfaction is estimated based on the costs incurred to date relative to the total estimated costs per the terms of each contract. The Company typically invoices BARDA monthly as costs are incurred. The base segment and first option segment were completed prior to adoption of ASC 606. The Company is currently performing under the second and third option segments of the contract during which the Company may receive up to a total of $23.9 million and $14.1 million in expense reimbursement and fees, respectively. The second option and third option segments are scheduled to end on August 1, 2019.

ContraVir Pharmaceuticals

The Company entered into a license agreement with ContraVir on December 17, 2014 for the development and commercialization of CMX157 for certain antiviral indications. The Company assessed the agreement in accordance with the authoritative guidance and concluded that the ContraVir contract includes multiple performance obligations, which had all been satisfied in 2015 prior to the adoption of ASC 606. The ContraVir contract has one fixed and several variable transaction amounts. The fixed fee portion of the contract was for the license to CMX157 rights. The Company recognized revenue for the fixed fee portion of the contract in 2015 when the performance obligations were satisfied. On April 2, 2019, the Company received notification from ContraVir of its intention to terminate the license agreement effective June 1, 2019.

Research and Development Prepaids and Accruals

As part of the process of preparing financial statements, the Company is required to estimate its expenses resulting from its obligation under contracts with vendors and consultants and clinical site agreements in connection with its research and development efforts. The financial terms of these contracts are subject to negotiations which vary contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts.

The Company’s objective is to reflect the appropriate research and development expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of its research and development efforts. The Company determines prepaid and accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of clinical trials, or other services completed. The Company adjusts its rate of research and development expense recognition if actual results differ from its estimates. The Company makes estimates of its prepaid and accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through March 31, 2019, there had been no material adjustments to the Company’s prior period estimates of prepaid and accruals for research and development expenses. The Company’s research and development prepaids and accruals are dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.

Basic and Diluted Net Loss Per Share of Common Stock

Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of non-vested restricted stock, stock options, and employee stock purchase plan purchase rights. Diluted net loss per share of common stock is computed by dividing net loss by the sum of the weighted-average number of shares of common stock outstanding during the period plus the potential dilutive effects of warrants to purchase common stock, non-vested restricted stock, stock options, and employee stock purchase plan purchase rights outstanding during the period calculated in accordance with the treasury stock method, but are excluded if their effect is anti-dilutive. Because the impact of these items is anti-dilutive during the periods of net loss, there was no difference between basic and diluted loss per share of common stock for the three months ended March 31, 2019 and 2018.

Impact of Recently Adopted Accounting Standards

In February 2016, the FASB issued Accounting Standards Update (ASU) No. 2016-02, “Leases (Topic 842)”, which has been amended through subsequent ASUs, and which increases transparency and comparability among companies accounting for lease transactions. The most significant change of this update requires the recognition of lease assets and liabilities on the balance sheet for lessees for operating lease arrangements with lease terms greater than 12 months. This ASU is effective for financial statements issued for annual periods and interim periods within those annual periods, beginning after December 15, 2018. The Company adopted this standard effective January 1, 2019 using the alternative modified retrospective adoption method allowed by ASU 2018-11. The Company elected to use the package of three practical expedients which allows the Company not to reassess whether contracts are or contain leases, lease classification, and whether initial direct costs qualify for capitalization. The Company has completed its assessment of the impact of the standard and determined that the only material leases that the Company holds are real estate operating leases. Upon adoption of the standard, the Company recorded a right of use asset of $1.4 million and lease liability of $1.6 million on its consolidated balance sheets with no adjustment to beginning retained earnings in the period of adoption.

Investments

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Investments

The following tables summarize the Company's debt investments (in thousands):



	March 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate bonds	$	54,675	$	36	$	(2	)	$	54,709
U.S. treasury securities	42,948		13		(1		)	42,960
Commercial paper	54,180		10		(8		)	54,182
Total investments	$	151,803	$	59	$	(11	)	$	151,851

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate bonds	$	32,724	$	—	$	(41	)	$	32,683
Commercial paper	60,159		—		(45		)	60,114
U.S. treasury securities	12,592		—		(3		)	12,589
Total investments	$	105,475	$	—	$	(89	)	$	105,386

The following tables summarize the Company's debt investments with unrealized losses, aggregated by investment type and the length of time that individual investments have been in a continuous unrealized loss position (in thousands, except number of securities):



	March 31, 2019
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate bonds	$	14,449	$	(2	)	$	—	$	—	$	14,449	$	(2	)
Commercial paper	19,807		(8		)	—		—		19,807		(8		)
U.S. treasury securities	6,724		(1		)	—		—		6,724		(1		)
Total	$	40,980	$	(11	)	$	—	$	—	$	40,980	$	(11	)
Number of securities with unrealized losses			12					—				12

	December 31, 2018
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate bonds	$	32,683	$	(41	)	$	—	$	—	$	32,683	$	(41	)
Commercial paper	60,114		(45		)	—		—		60,114		(45		)
U.S. treasury securities	12,589		(3		)	—		—		12,589		(3		)
Total	$	105,386	$	(89	)	$	—	$	—	$	105,386	$	(89	)
Number of securities with unrealized losses			36					—				36

The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. The Company evaluates, among other things, the duration and extent to which the fair value of a security is less than its cost; the financial condition of the issuer and any changes thereto; and the Company’s intent to sell, or whether it will more likely than not be required to sell, the security before recovery of its cost basis. At March 31, 2019, the Company did not intend to sell, and was not more likely than not to be required to sell, the available-for-sale debt securities in an unrealized loss position before recovery of the cost basis of the securities, which may be at maturity. There were no such declines in value for the three months ended March 31, 2019 and 2018. Unrealized gains and losses on debt investments are recorded to unrealized gain (loss) on investments, net in the Consolidated Statements of Operations and Comprehensive Loss. The Company recognizes interest income on an accrual basis in interest income in the Consolidated Statements of Operations and Comprehensive Loss.

The following table summarizes the scheduled maturity for the Company's debt investments at March 31, 2019 (in thousands):



Maturing in one year or less	$	151,851
Maturing after one year through two years	—
Total debt investments	151,851
Common stock of U.S. corporation	30
Total investments	$	151,881

Commitments and Contingencies

3 Months Ended

Mar. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Leases

The Company leases its facilities under long-term operating leases that expire at various dates through 2021. The Company generally has options to renew lease terms on its facilities, which may be exercised at the Company's sole discretion. In addition, certain lease arrangements may be terminated prior to their original expiration date at the Company's discretion. The Company evaluates renewal and termination options at the lease commencement date to determine if it is reasonably certain to exercise the option and have concluded on all operating leases that it is not reasonably certain that any options will be exercised. The weighted-average remaining lease term for the Company's operating leases as of March 31, 2019 was 2.06 years.

Expense related to leases is recorded on a straight-line basis over the lease term. Lease expense under operating leases, including common area maintenance fees, totaled approximately $0.2 million for the three months ended March 31, 2019 and 2018.

The discount rate implicit within the Company's leases is generally not determinable and therefore the Company determines the discount rate based on its incremental borrowing rate based on the information available at commencement date. As of March 31, 2019, the operating lease liabilities reflect a weighted-average discount rate of 13.16%.

The following table sets forth the operating lease right-of-use assets and liabilities as of March 31, 2019 (in thousands):



Assets
Operating Lease Right-of-Use Assets	$	1,232

Liabilities
Operating Lease Short-term Liabilities (recorded within Accrued liabilities)	$	640
Operating Lease Long-term Liabilities (recorded within Lease-related obligations)	782
Total Operating Lease Liabilities	$	1,422

Operating lease payments over the remainder of the lease terms are as follows (in thousands):



Years Ending December 31,	As of March 31, 2019
2019	$	585
2020	797
2021	235
Total future minimum rental payments	$	1,617
Less amount of lease payments representing interest	195
Total present value of lease payments	$	1,422

As of December 31, 2018, future minimum payments under operating leases under ASC 840 were as follows (in thousands):



Years Ending December 31,	As of December 31, 2018
2019	$	786
2020	797
2021	235
Total future minimum rental payments	$	1,818

For the three months ended March 31, 2019 and 2018, the Company made lease payments of approximately $192,000 and $184,000, respectively, which are included in operating cash flows.

Sublease

The Company subleases 3,537 square feet of its office space under a non-cancelable operating lease that expires in February 2021. For the three months ended March 31, 2019, the Company recognized approximately $18,000 of income in Interest income and other, net on the Consolidated Statement of Operations and Comprehensive Loss. For the three months ended March 31, 2018, the Company recognized approximately $18,000 of a reduction of rent expense in operating expenses on the Consolidated Statement of Operations and Comprehensive Loss. Total future minimum rentals under the non-cancelable operating sublease are presented below (in thousands):



Years Ending December 31,	As of March 31, 2019
2019	$	58
2020	81
2021	14
Total future minimum sublease rentals	$	153

Significance of Revenue Source

The Company is the recipient of federal research contract funds from BARDA, the sole source of the Company's contract revenue. Periodic audits are required under the Company’s BARDA agreement and certain costs may be questioned as appropriate under the BARDA agreement. Management believes that such amounts in the current year, if any, are not significant. Accordingly, no provision for refundable amounts under the BARDA agreement had been made as of March 31, 2019 and December 31, 2018.

Equity Transactions and Share-based Compensation

3 Months Ended

Mar. 31, 2019

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

Equity Transactions and Share-based Compensation

Stock Options

In connection with the Company’s IPO, the Company adopted the 2013 Equity Incentive Plan (the 2013 Plan). The 2013 Plan provides for the grant of incentive stock options (ISOs), non-statutory stock options (NSOs), stock appreciation rights, restricted stock awards, restricted stock unit (RSU) awards, performance-based stock awards, and other forms of equity compensation (collectively, stock awards), all of which may be granted to employees, including officers, non-employee directors and consultants of the Company and its affiliates. Additionally, the 2013 Plan provides for the grant of performance cash awards. The number of shares of common stock reserved for future issuance automatically increases on January 1 of each calendar year by 4% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. On January 1, 2019, the common stock reserved for issuance under the 2013 Plan was automatically increased by 2.0 million shares. As of March 31, 2019, there was a total of 1.5 million shares reserved for future issuance under the 2013 Plan. The Company issued approximately 8,000 shares of common stock pursuant to the exercise of stock options during the three months ended March 31, 2019.

Employee Stock Purchase Plan

In February 2013, the Company’s board of directors adopted the 2013 Employee Stock Purchase Plan (ESPP), which was subsequently ratified by stockholders and became effective in April 2013. Initially, the ESPP authorized the issuance of 704,225 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of its designated affiliates. The number of shares of common stock reserved for issuance automatically increases on January 1 of each calendar year, from January 1, 2014 through January 1, 2023 by the lesser of (a) 1% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (b) 422,535 shares, or (c) a number determined by the Company’s board of directors that is less than (a) and (b). On January 1, 2019, the common stock reserved for issuance under the ESPP was automatically increased by an additional 422,535 shares.

The Company has reserved a total of 3.1 million shares of common stock to be purchased under the ESPP, of which 2.4 million shares remained available for purchase as of March 31, 2019. The ESPP provides for an automatic reset feature to start participants on a new twenty-four month participation period in the event that the common stock market value on a purchase date is less than the common stock value on the first day of the twenty-four month offering period. Eligible employees may authorize an amount up to 15% of their salary to purchase common stock at the lower of a 15% discount to the beginning price of their offering period or a 15% discount to the ending price of each six-month purchase interval. The Company issued approximately 113,000 shares of common stock pursuant to the ESPP during the three months ended March 31, 2019. Compensation expense for shares purchased under the ESPP related to the purchase discount and the “look-back” option and were determined using a Black-Scholes option pricing model.

Restricted Stock Units

The Company has issued RSUs to certain employees which vest based on service criteria. When vested, the RSU represents the right to be issued the number of shares of the Company's common stock that is equal to the number of RSUs granted. The grant date fair value for RSUs is based upon the market price of the Company's common stock on the date of the grant. The fair value is then amortized to compensation expense over the requisite service period or vesting term. The Company issued approximately 168,000 shares of common stock pursuant to the vesting of RSUs during the three months ended March 31, 2019.

Stock-based Compensation

For awards with only service conditions and graded-vesting features, the Company recognizes compensation expense on a straight-line basis over the requisite service period. Total share-based compensation expense recognized related to stock options, the ESPP and RSUs was as follows (in thousands):



	Three Months Ended March 31,
	2019		2018
Research and development expense	$	1,270	$	1,320
General and administrative expense	2,803		2,071
Total share-based compensation expense	$	4,073	$	3,391

On February 5, 2019, Dr. M. Michelle Berrey, the Company's then President and Chief Executive Officer, resigned. The Company entered into a severance agreement with Dr. Berrey that provides for severance benefits to her in connection with her resignation. Among other benefits, Dr. Berrey received accelerated vesting of her outstanding stock options and RSUs as if she had continued service for an additional 15 month period. In addition, Dr. Berrey's vested options were modified to extend her exercise period to May 5, 2020. The Company recorded a charge of $1.8 million to compensation expense on the date of her resignation related to the acceleration of vesting and the modifications of her outstanding stock options and RSUs.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company estimates an annual effective tax rate of 0% for the year ending December 31, 2019 as the Company incurred losses for the three month period ended March 31, 2019 and is forecasting additional losses through the fourth quarter, resulting in an estimated net loss for both financial statement and tax purposes for the year ending December 31, 2019. Therefore, no federal or state income taxes are expected and none have been recorded at this time. Income taxes have been accounted for using the liability method in accordance with FASB ASC 740. Due to the Company's history of losses since inception, there is not enough evidence at this time to support that the Company will generate future income of a sufficient amount and nature to utilize the benefits of its net deferred tax assets. Accordingly, the deferred tax assets have been reduced by a full valuation allowance, since the Company does not currently believe that realization of its deferred tax assets is more likely than not. At March 31, 2019, the Company had no unrecognized tax benefits that would reduce the Company’s effective tax rate if recognized.

Significant Agreements	3 Months Ended
Significant Agreements	Mar. 31, 2019
Revenue Recognition [Abstract]
Significant Agreements	Significant Agreements The Regents of the University of California In May 2002, the Company entered into a license agreement with The Regents of the University of California (UC) under which the Company obtained an exclusive, worldwide license to UC’s patent rights in certain inventions (the UC Patent Rights) related to lipid-conjugated antiviral compounds and their use, including certain patents relating to brincidofovir. The license agreement was amended in September 2002 in order to expand the scope of the license and again in December 2010 in order to modify certain financial terms. The agreement was amended a third time in September 2011 to add additional patents related to certain metabolically stable lipid-conjugate compounds. A fourth amendment was executed in July 2012 to alter the rights and obligations of the parties in light of the Company's current business plans. In April 2018, a fifth amendment was executed to alter the rights and obligations of the parties in light of the Company's current business plans and to extend the term of the agreement to the later of the longest-lived Patent Rights (as defined in the agreement) or May 2028. Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UC Patent Rights for all human and veterinary uses, and to sublicense such rights. UC retained the right, on behalf of itself and other non-profit institutions, to use the UC Patent Rights for educational and research purposes and to publish information about the UC Patent Rights. In consideration for the rights granted under the license agreement, the Company has issued UC an aggregate of 64,788 shares of common stock. As additional consideration, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights, plus certain annual fees to maintain such patents until the Company commercializes a product utilizing UC Patent Rights. In connection with the development and commercialization of brincidofovir and CMX157, the Company could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement. In addition, upon commercialization of any product utilizing the UC Patent Rights (which would include the commercialization of brincidofovir), the Company will be required to pay low single digit royalties on net sales of such product. The license agreement requires that we diligently develop, manufacture and commercialize compounds that are covered by the UC Patent Rights, and we have agreed to meet certain development and commercialization milestones. UC may, at its option, either terminate the license agreement or change the license granted from an exclusive license to a non-exclusive license if we fail to meet such development and commercialization milestones. We are currently in compliance with these milestone requirements. In the event the Company sublicenses a UC Patent Right (including UC Patent Rights relating to brincidofovir or CMX157) the Company is obligated to pay to UC a fee, which amount will vary depending upon the amount of any payments the Company receives and the clinical development stage of the compound being sublicensed, but which could be up to approximately 50% of the sublicense fee in certain circumstances. With respect to brincidofovir, the fee payable to UC will not exceed 5% of the sublicense fee. In addition, the Company will also be required to pay to UC a low single digit sublicense royalty on net sales of products that use the sublicensed UC Patent Rights, but in no event will the Company be required to pay more than 50% of the royalties it receives in connection with the relevant sublicense. Any such royalty payment will be reduced by other payments the Company is required to make to third parties until a minimum royalty has been reached. Biomedical Advanced Research and Development Authority (BARDA) In February 2011, the Company entered into a contract with BARDA for the advanced development of brincidofovir as a medical countermeasure in the event of a smallpox release. Under the contract, BARDA will reimburse the Company, plus pay a fixed fee, for the research and development of brincidofovir as a broad-spectrum therapeutic antiviral for the treatment of smallpox infections. The contract consists of an initial performance period, referred to as the base performance segment, plus up to four extension periods, referred to as option segments, each of which may be exercised at BARDA’s sole discretion. The Company must complete the agreed upon milestones and deliverables in each discrete work segment before the next option segment is eligible to be exercised. Under the contract as currently in effect, the Company may receive up to $75.8 million in expense reimbursement and $5.3 million in fees. The Company is currently performing under the second and third option segments of the contract during which the Company may receive up to a total of $23.9 million and $14.1 million in expense reimbursement and fees, respectively. The second and third option segments are scheduled to end on August 1, 2019. Of the $75.8 million in expense reimbursement and $5.3 million in fees that the Company may receive, approximately $74.3 million in expense reimbursement and fees has been funded. As of March 31, 2019, of the total funding the Company had invoiced an aggregate of $64.9 million with respect to the base performance segment and the first three option segments. For the three months ended March 31, 2019 and 2018, the Company recognized revenue under this contract of $2.4 million and $0.8 million, respectively. ContraVir Pharmaceuticals On December 17, 2014, the Company entered into a license agreement with ContraVir (Nasdaq:CTRV) for the development and commercialization of CMX157 for certain antiviral indications. Under the terms of the agreement, ContraVir has sole responsibility with respect to the control of the development and commercialization of CMX157. In exchange for the license to CMX157 rights, the Company received an upfront payment consisting of ContraVir Series B Convertible Preferred Stock which the Company converted into shares of ContraVir common stock in 2016. As of March 31, 2019 and December 31, 2018, the fair value of the investment was recorded as a short-term investment of approximately $30,000 and $38,000, respectively. On April 2, 2019 the Company received notification from ContraVir of its intention to terminate the license agreement effective June 1, 2019. University of Michigan In 2006, the Company entered into a license agreement with The Regents of the University of Michigan (UM) under which the Company obtained an exclusive, worldwide license to UM’s patent rights in certain inventions (UM Patent Rights) related to certain compounds originally synthesized at UM. Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UM Patent Rights, and to sublicense such rights subject to certain sublicensing fees and royalty payments. In consideration for the rights granted to the Company, under the license agreement as amended in December 2016, the Company paid UM $50,000 in fees in 2016 and in January 2017 issued UM an aggregate of 33,058 shares of its common stock. In connection with the Company's commercialization or sublicensing of certain products covered by the license agreement, including CMX521, the Company could be required to pay royalties on net sales of such products ranging from 0.25% to 2%. Beginning in 2024, the Company is also subject to certain minimum annual royalty payments. The UM license agreement requires that the Company uses commercially reasonable efforts to develop and make commercially available licensed products as soon as practicable. Specifically, the Company has agreed to make the first commercial sale of a licensed product by June of 2026. UM may terminate the license agreement if the Company materially breaches the license agreement. The Company is currently in compliance with its milestone requirements.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events through the issuance date of these financial statements to ensure that this filing includes appropriate disclosure of events both recognized in the financial statements as of March 31, 2019, and events which occurred subsequently but were not recognized in the financial statements.

The Business and Summary of Significant Accounting Policies (Policy)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Basis of Presentation

Fair Value of Financial Instruments


•	Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.


•	Level 2 — Valuations based on quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and models for which all significant inputs are observable, either directly or indirectly.


•	Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.

Revenue Recognition

Policy

Research and Development Prepaids and Accruals

Basic and Diluted Net Loss Per Share of Common Stock

Impact of Recently Issued Accounting Standards and Impact of Recently Adopted Accounting Standards

Impact of Recently Adopted Accounting Standards

The Business and Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Schedule of certain assets measured at fair value on a recurring basis

Below are tables that present information about certain assets measured at fair value on a recurring basis (in thousands):



	Fair Value Measurements
	March 31, 2019
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	11,879	$	11,879	$	—	$	—
Commercial paper	2,699		—		2,699		—
Corporate bonds	2,000		—		2,000		—
Total cash equivalents	16,578		11,879		4,699		—
Short-term investments
U.S. treasury securities	42,960		42,960		—		—
Common stock of U.S. corporation	30		30		—		—
Commercial paper	54,182		—		54,182		—
Corporate bonds	54,709		—		54,709		—
Total short-term investments	151,881		42,990		108,891		—
Total assets	$	168,459	$	54,869	$	113,590	$	—

	Fair Value Measurements
	December 31, 2018
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	30,726	$	30,726	$	—	$	—
U.S. treasury securities	11,482		11,482		—		—
Commercial paper	29,677		—		29,677		—
Corporate bonds	4,008		—		4,008		—
Total cash equivalents	75,893		42,208		33,685		—
Short-term investments
U.S. treasury securities	12,589		12,589		—		—
Common stock of U.S. corporation	38		38		—		—
Commercial paper	60,114		—		60,114		—
Corporate bonds	32,683		—		32,683		—
Total short-term investments	105,424		12,627		92,797		—
Total assets	$	181,317	$	54,835	$	126,482	$	—

Schedule of accrued liabilities

Accrued liabilities consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Accrued research and development expenses	$	5,823	$	4,525
Accrued compensation	2,453		2,469
Other accrued liabilities	2,113		1,281
Total accrued liabilities	$	10,389	$	8,275

Investments (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Summary of short-term and long-term investments

The following tables summarize the Company's debt investments (in thousands):



	March 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate bonds	$	54,675	$	36	$	(2	)	$	54,709
U.S. treasury securities	42,948		13		(1		)	42,960
Commercial paper	54,180		10		(8		)	54,182
Total investments	$	151,803	$	59	$	(11	)	$	151,851

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate bonds	$	32,724	$	—	$	(41	)	$	32,683
Commercial paper	60,159		—		(45		)	60,114
U.S. treasury securities	12,592		—		(3		)	12,589
Total investments	$	105,475	$	—	$	(89	)	$	105,386

Summary of investments with unrealized losses, aggregated by investment type and the length of time



	March 31, 2019
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate bonds	$	14,449	$	(2	)	$	—	$	—	$	14,449	$	(2	)
Commercial paper	19,807		(8		)	—		—		19,807		(8		)
U.S. treasury securities	6,724		(1		)	—		—		6,724		(1		)
Total	$	40,980	$	(11	)	$	—	$	—	$	40,980	$	(11	)
Number of securities with unrealized losses			12					—				12

	December 31, 2018
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate bonds	$	32,683	$	(41	)	$	—	$	—	$	32,683	$	(41	)
Commercial paper	60,114		(45		)	—		—		60,114		(45		)
U.S. treasury securities	12,589		(3		)	—		—		12,589		(3		)
Total	$	105,386	$	(89	)	$	—	$	—	$	105,386	$	(89	)
Number of securities with unrealized losses			36					—				36

Summary of the scheduled maturity of company investments

The following table summarizes the scheduled maturity for the Company's debt investments at March 31, 2019 (in thousands):



Maturing in one year or less	$	151,851
Maturing after one year through two years	—
Total debt investments	151,851
Common stock of U.S. corporation	30
Total investments	$	151,881

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Operating Lease Right-of-Use Assets and Liabilities

The following table sets forth the operating lease right-of-use assets and liabilities as of March 31, 2019 (in thousands):



Assets
Operating Lease Right-of-Use Assets	$	1,232

Liabilities
Operating Lease Short-term Liabilities (recorded within Accrued liabilities)	$	640
Operating Lease Long-term Liabilities (recorded within Lease-related obligations)	782
Total Operating Lease Liabilities	$	1,422

Operating Lease Maturity

Operating lease payments over the remainder of the lease terms are as follows (in thousands):



Years Ending December 31,	As of March 31, 2019
2019	$	585
2020	797
2021	235
Total future minimum rental payments	$	1,617
Less amount of lease payments representing interest	195
Total present value of lease payments	$	1,422

Operating Lease Maturity

As of December 31, 2018, future minimum payments under operating leases under ASC 840 were as follows (in thousands):



Years Ending December 31,	As of December 31, 2018
2019	$	786
2020	797
2021	235
Total future minimum rental payments	$	1,818

Sublease Income

Total future minimum rentals under the non-cancelable operating sublease are presented below (in thousands):



Years Ending December 31,	As of March 31, 2019
2019	$	58
2020	81
2021	14
Total future minimum sublease rentals	$	153

Equity Transactions and Share-based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

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

Schedule of employee and non-employee share-based compensation expense recognized related to stock options, the ESPP and RSUs

Total share-based compensation expense recognized related to stock options, the ESPP and RSUs was as follows (in thousands):



	Three Months Ended March 31,
	2019		2018
Research and development expense	$	1,270	$	1,320
General and administrative expense	2,803		2,071
Total share-based compensation expense	$	4,073	$	3,391

The Business and Summary of Significant Accounting Policies - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Accrued research and development expenses	$ 5,823	$ 4,525
Accrued compensation	2,453	2,469
Other accrued liabilities	2,113	1,281
Total accrued liabilities	$ 10,389	$ 8,275

The Business and Summary of Significant Accounting Policies - Revenue Recognition (Details) $ in Thousands	3 Months Ended		98 Months Ended	102 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Aug. 01, 2019 USD ($) base_segment revenue_contract option_segment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue	$ 2,356	$ 790
BARDA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue	$ 2,400	$ 800	$ 64,900
Scenario, Forecast \| BARDA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue				$ 74,300
Total number of base segments \| base_segment				1
Total number of option segments \| option_segment				4
Total number of separate contracts \| revenue_contract				5
Scenario, Forecast \| BARDA Second Option Segment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue				$ 23,900
Scenario, Forecast \| BARDA Third Option Segment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue				14,100
Expense reimbursement \| Scenario, Forecast \| BARDA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue				75,800
Fees \| Scenario, Forecast \| BARDA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue				$ 5,300

The Business and Summary of Significant Accounting Policies - Impact of Recently Adopted Accounting Standards (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 1,232
Operating lease liability	$ 1,422
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 1,400
Operating lease liability		$ 1,600

Investments - Summary of Available-for-Sale securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Amortized Cost	$ 151,803	$ 105,475
Gross Unrealized Gains	59	0
Gross Unrealized Losses	(11)	(89)
Estimated Fair Value	151,851	105,386
Corporate bonds
Schedule of Investments [Line Items]
Amortized Cost	54,675	32,724
Gross Unrealized Gains	36	0
Gross Unrealized Losses	(2)	(41)
Estimated Fair Value	54,709	32,683
U.S. treasury securities
Schedule of Investments [Line Items]
Amortized Cost	42,948	12,592
Gross Unrealized Gains	13	0
Gross Unrealized Losses	(1)	(3)
Estimated Fair Value	42,960	12,589
Commercial paper
Schedule of Investments [Line Items]
Amortized Cost	54,180	60,159
Gross Unrealized Gains	10	0
Gross Unrealized Losses	(8)	(45)
Estimated Fair Value	$ 54,182	$ 60,114

Investments - Summary of Investments with Unrealized Losses, Aggregated by Investment Type and the Length of Time (Details) $ in Thousands	Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 40,980	$ 105,386
Unrealized Loss, Less than 12 Months	(11)	(89)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	40,980	105,386
Unrealized Loss, Total	$ (11)	$ (89)
Number of securities with unrealized losses, Less than 12 Months \| security	12	36
Number of securities with unrealized losses, Greater than 12 Months \| security	0	0
Number of securities with unrealized losses, Total \| security	12	36
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 14,449	$ 32,683
Unrealized Loss, Less than 12 Months	(2)	(41)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	14,449	32,683
Unrealized Loss, Total	(2)	(41)
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	19,807	60,114
Unrealized Loss, Less than 12 Months	(8)	(45)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	19,807	60,114
Unrealized Loss, Total	(8)	(45)
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	6,724	12,589
Unrealized Loss, Less than 12 Months	(1)	(3)
Fair Value, Greater than 12 Months	0	0
Unrealized Loss, Greater than 12 Months	0	0
Fair Value, Total	6,724	12,589
Unrealized Loss, Total	$ (1)	$ (3)