Chimerix (CMRX) 10-K 7 Mar 14 2013 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Feb. 26, 2014	Jun. 28, 2013
Document Document And Entity Information [Abstract]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Entity Registrant Name	'CHIMERIX INC	'	'
Entity Central Index Key	'0001117480	'	'
Entity Voluntary Filers	'No	'	'
Entity Well-known Seasoned Issuer	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Non-accelerated Filer	'	'
Entity Public Float	'	'	$295,687,107	[1]
Entity Common Stock, Shares Outstanding	'	26,762,934	'
[1]	Based on a closing price of $24.24 per share on June 28, 2013. Excludes 13,581,132 shares of the registrant's Common Stock held by executive officers, directors and any stockholders whose ownership exceeds 5% of registrant's Common Stock outstanding at June 28, 2013. Exclusion of such shares should not be construed to indicate that any such person possesses the power, direct or indirect, to direct or cause the direction of the management or policies of the registrant or that such person is controlled by or under common control with the registrant.

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$109,976	$19,906
Short-term investments, available-for-sale	'	9,849
Accounts receivable	248	783
Prepaid and other current assets	2,765	983
Deferred financing costs, current portion	20	33
Total current assets	113,009	31,554
Property and equipment, net of accumulated depreciation	338	407
Deposits and prepaid assets, less current portion	30	22
Deferred financing costs, less current portion	10	48
Total assets	113,387	32,031
Current liabilities:	'	'
Accounts payable	2,214	1,964
Accrued liabilities	2,420	906
Loan payable, current portion	5,573	4,753
Total current liabilities	10,207	7,623
Other long-term liabilities	347	337
Loan payable, less current portion	4,294	9,867
Redeemable convertible preferred stock warrant liability	'	7,512
Total liabilities	14,848	25,339
Redeemable convertible preferred stock	'	107,723
Stockholders' equity (deficit):	'	'
Common stock, $0.001 par value, 200,000,000 and 89,700,000 shares authorized at December 31, 2013 and 2012, respectively; 26,664,972 and 1,533,996 shares issued and outstanding at December 31, 2013 and 2012, respectively	26	3
Additional paid-in capital	261,243	'
Accumulated other comprehensive loss	'	-2
Accumulated deficit	-162,730	-101,032
Total stockholders' equity (deficit)	98,539	-101,031
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$113,387	$32,031

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Balance Sheets [Abstract]	'	'
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	200,000,000	89,700,000
Common stock, shares issued	26,664,972	1,533,996
Common stock, shares outstanding	26,664,972	1,533,996

Statements_of_Operations_and_C

Statements of Operations and Comprehensive Loss (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:	'	'	'
Contract revenue	$4,370	$16,275	$12,046
Collaboration and licensing revenue	'	17,445	55
Total revenues	4,370	33,720	12,101
Operating expenses:	'	'	'
Research and development	24,662	30,106	30,108
General and administrative	8,327	6,397	6,985
Total operating expenses	32,989	36,503	37,093
Loss from operations	-28,619	-2,783	-24,992
Other expense:	'	'	'
Interest expense, net	-1,232	-776	-212
Fair value adjustments to warrant liability	-6,590	-847	-385
Loss on asset disposal	-4	'	'
Net loss	-36,445	-4,406	-25,589
Other comprehensive loss:	'	'	'
Unrealized gain (loss) on securities available-for-sale	2	2	-4
Comprehensive loss	-36,443	-4,404	-25,593
Accretion of redeemable convertible preferred stock	-34,108	-4,357	-9,565
Net (loss) income attributable to common shareholders	($70,553)	($8,763)	($35,154)
Per share information:	'	'	'
Net loss, basic and diluted	($3.65)	($5.75)	($23.49)
Weighted-average shares outstanding, basic and diluted	19,307,422	1,524,628	1,496,262

Statements_of_Redeemable_Conve

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Total
In Thousands, unless otherwise specified
Beginning balance at Dec. 31, 2010	$55,131	$2	$1,895	'	($61,504)	($59,607)
Share-based compensation	'	'	966	'	'	966
Issuance of redeemable convertible preferred stock	38,670	'	'	'	'	'
Issuance of common stock	'	'	89	'	'	89
Exercise of stock options	'	'	30	'	'	30
Dividends on redeemable preferred stock	3,235	'	-2,980	'	-255	-3,235
Adjustment of redeemable preferred stock to redemption value	6,330	'	'	'	-6,330	-6,330
Comprehensive loss:	'	'	'	'	'	'
Unrealized (loss) gain on investments, net	'	'	'	-4	'	-4
Net loss	'	'	'	'	-25,589	-25,589
Comprehensive loss	'	'	'	'	'	-25,593
Ending balance at Dec. 31, 2011	103,366	2	'	-4	-93,678	-93,680
Share-based compensation	'	'	1,396	'	'	1,396
Exercise of stock options	'	1	13	'	'	14
Dividends on redeemable preferred stock	3,600	'	-1,409	'	-2,191	-3,600
Adjustment of redeemable preferred stock to redemption value	757	'	'	'	-757	-757
Comprehensive loss:	'	'	'	'	'	'
Unrealized (loss) gain on investments, net	'	'	'	2	'	2
Net loss	'	'	'	'	-4,406	-4,406
Comprehensive loss	'	'	'	'	'	-4,404
Ending balance at Dec. 31, 2012	107,723	3	'	-2	-101,032	-101,031
Share-based compensation	'	'	3,071	'	'	3,071
Issuance of common stock	'	23	107,611	'	'	107,634
Exercise of stock options	'	'	1,946	'	'	1,946
Dividends on redeemable preferred stock	976	'	-349	'	-627	-976
Adjustment of redeemable preferred stock to redemption value	33,132	'	-8,506	'	-24,626	-33,132
Comprehensive loss:	'	'	'	'	'	'
Unrealized (loss) gain on investments, net	'	'	'	2	'	2
Net loss	'	'	'	'	-36,445	-36,445
Comprehensive loss	'	'	'	'	'	-36,443
Exercise of warrants	'	'	1,537	'	'	1,537
Conversion of redeemable preferred stock into common stock	-141,831	'	141,831	'	'	141,831
Reclassification of redeemable preferred stock warrant liability to additional paid in capital	'	'	14,102	'	'	14,102
Ending balance at Dec. 31, 2013	'	$26	$261,243	'	($162,730)	$98,539

Statements_of_Redeemable_Conve1

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2013
Statement of Stockholders' Equity [Abstract]	'
Issuance of common stock, shares	8,418,000
Issuance of common stock, per share price	$14
Issuance of common stock, issuance costs	$10,217,696

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:	'	'	'
Net (loss) income	($36,445)	($4,406)	($25,589)
Adjustments to reconcile net loss to net cash used in operating activities:	'	'	'
Depreciation	258	280	270
Non-cash interest expense	248	238	50
Amortization/accretion of premium/discount on investments	196	84	118
Loss on disposal of equipment	4	'	'
Share-based compensation costs	3,071	1,396	1,055
Deferred lease obligation	10	'	-4
Fair value measurement of redeemable convertible preferred stock warrant liability	6,590	847	385
Net change in:	'	'	'
Accounts receivable	535	3,404	-4,187
Prepaid and other current assets and deposits	-1,790	65	-442
Accounts payable and accrued liabilities	1,764	-3,784	2,065
Net cash used in operating activities	-25,559	-1,876	-26,279
Investing Activities:	'	'	'
Purchase of property and equipment	-193	-126	-321
Purchase of short-term investments	-1,852	-9,907	-13,640
Sales of short-term investments	750	'	500
Maturities of short-term investments	10,757	5,894	7,100
Repayment of loan to officer	'	'	125
Net cash provided by (used in) investing activities	9,462	-4,139	-6,236
Financing Activities:	'	'	'
Proceeds from issuance of redeemable convertible preferred stock and warrants	'	'	45,000
Proceeds from exercise of stock options	1,946	14	30
Proceeds from exercise of warrants	1,537	'	'
Proceeds from loan payable	'	15,000	'
Proceeds from initial public offering, net of offering costs	107,634	'	'
Debt discount	'	-75	'
Repayment of loan payable	-4,950	-2,601	-1,965
Stock offering and deferred financing costs	'	-24	-249
Net cash provided by financing activities	106,167	12,314	42,816
Increase in cash and cash equivalents	90,070	6,299	10,301
Cash and cash equivalents, beginning of period	19,906	13,607	3,306
Cash and cash equivalents, end of period	109,976	19,906	13,607
Supplemental cash flow information:	'	'	'
Interest payments	$1,092	$448	$186

The_Business_and_Summary_of_Si

The Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
The Business and Summary of Significant Accounting Policies [Abstract]	'
The Business and Summary of Significant Accounting Policies	'
	1. The Business and Summary of Significant Accounting Policies
	Description of Business
	Chimerix is a biopharmaceutical company dedicated to discovering, developing and commercializing novel, oral antivirals to address unmet medical needs.  The Company was founded in 2000 based on the promise of its proprietary lipid technology to unlock the potential of some of the most potent antivirals by enhancing their antiviral activity and safety profiles in convenient, orally administered dosing regiments.  Based on the Company’s lipid technology, its lead compound, brincidofovir (CMX001) is in Phase 3 clinical development, its second compound, CMX157, was licensed to Merck after completing a Phase 1 study and the Company has an active discovery program focusing on viral targets for which no therapies are currently available.
	On March 25, 2013, the Company’s board of directors approved and implemented a 3.55-for-1 reverse stock split of the Company’s outstanding common stock. The reverse stock split resulted in an adjustment to the preferred stock conversion price to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented.
	On April 10, 2013, the Company completed the initial public offering (IPO) of its common stock pursuant to a registration statement on Form S-1. In the IPO, the Company sold an aggregate of 7,320,000 shares of common stock under the registration statement at a public offering price of $14.00 per share. Net proceeds were approximately $93.3 million, after deducting underwriting discounts and commissions of $7.1 million and offering expenses of $2.1 million. Upon the completion of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock and dividends accrued on Series F redeemable convertible preferred stock were converted into 15,556,091 shares of common stock and all outstanding warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase 1,613,395 shares of common stock. On April 16, 2013, the underwriters exercised the full over-allotment option pursuant to which the Company sold an additional 1,098,000 shares at $14.00 per share. Net proceeds from the over-allotment shares were approximately $14.3 million after deducting underwriting discounts and commissions of $1.1 million.
	On October 23, 2013, the Company completed an underwritten secondary public offering of 2,476,995 shares of common stock held by certain of the Company’s existing stockholders. The Company did not issue any shares of common stock and received no proceeds in connection with such offering. The principal purposes of the offering were to facilitate an orderly distribution of shares and to increase the Company’s public float.
	The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The preparation of the Company’s financial statements requires estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the financial statements and accompanying notes. Although these estimates are based on knowledge of current events and actions the Company may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
	Cash and Cash Equivalents
	The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market accounts.
	Investments
	Investments consist primarily of corporate bonds and commercial paper. The Company invests in high-credit quality investments in accordance with its investment policy which minimizes the probability of loss.
	Available-for-sale securities are carried at fair value as determined by quoted market prices, with the unrealized gains and losses, net of tax, reported as a separate component of stockholders deficit. Realized gains and losses are determined using the specific identification method and transactions are recorded on a settlement date basis in interest income or expense, net. Investments with original maturities beyond three months at the date of purchase and which mature on, or less than twelve months from, the balance sheet date are classified as long-term. The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Any such declines in value judged to be other-than-temporary on available-for-sale securities are reported in interest income or expense, net. There were no such declines in value for the years ended December 31, 2013 and 2012.
	Concentration of Credit Risk
	Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, short-term investments and accounts receivable. The Company is exposed to credit risk, subject to federal deposit insurance, in the event of default by the financial institutions holding its cash and cash equivalents to the extent of amounts recorded on the balance sheets. Accounts receivable represent amounts due from an agency of the federal government.
	Accounts Receivable
	Accounts receivable at December 31, 2013 and December 31, 2012 consisted of amounts billed and unbilled under the Company’s contract with the Biomedical Advanced Research and Development Authority (BARDA). Receivables under the BARDA contract are recorded as qualifying research activities as conducted and invoices from the Company’s vendors are received. The Company carries its accounts receivable at cost less an allowance for doubtful accounts. On a periodic basis, the Company evaluates its accounts receivable and establishes an allowance based on its history of collections and write-offs and the current status of all receivables. The Company does not accrue interest on trade receivables. If accounts become uncollectible, they will be written off through a charge to the allowance for doubtful accounts. The Company has not recorded a charge to allowance for doubtful accounts as management believes all receivables are fully collectible.
	Fair Value of Financial Instruments
	The carrying amounts of certain financial instruments, including accounts receivable, notes receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of such instruments. The carrying amount of borrowings under loans payable approximates its fair value based on the determination that the stated rate on such loans payable is consistent with current interest rates for similar borrowing arrangements available to the Company.
	For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements, in accordance with the fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates and are often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, fair value measurements cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the calculated current or future fair values. The Company utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures.
	The Company groups assets and liabilities at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. An adjustment to the pricing method used within either Level 1 or Level 2 inputs could generate a fair value measurement that effectively falls in a lower level in the hierarchy. These levels are:
		·	Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.
		·	Level 2 — Valuations based on quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and models for which all significant inputs are observable, either directly or indirectly.
		·	Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.
	The determination of where an asset or liability falls in the hierarchy requires significant judgment. The Company evaluates hierarchy disclosures and, based on various factors, it is possible that an asset or liability may be classified differently from period to period. However, the Company expects that changes in classification between levels will be rare.
	The Company has cash equivalents, consisting of money market accounts and commercial paper, whose value is based on using quoted market prices. Accordingly, these securities are classified as Level 1.
	At December 31, 2012, the Company had short-term investments, comprised of corporate bonds and commercial paper, for which quoted prices are not available that were valued using independent pricing models or other model-based valuation techniques such as the present value of future cash flows, adjusted for the security’s credit rating, prepayment assumptions and other factors such as credit loss assumptions. Accordingly, these securities are classified as Level 2.
	The warrants issued for Series F redeemable convertible preferred stock included in the Company’s 2012 financial statements are categorized as Level 3 as there are significant unobservable inputs. The valuation of the warrants at December 31, 2012 reflected a two stage process. Using a contingent claims model in combination with the Company’s Series F financing, which occurred in February 2011, the fair value of total equity and all components of the Company’s capital structure, including the warrants, was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities consistent with market practice, a distribution of equity values was produced which covered the range of values that an informed market participant might expect. These outcomes were organized into ranges and a probability calculated based on the percent of the total falling into each range. This process created a range of equity values. Using a contingent claims framework, each equity value was allocated to the various components of the capital structure including the warrants. Each warrant value was weighted by its respective probability to determine the final fair value of the warrants as of December 31, 2012. The key unobservable inputs used in the determination of the fair value were (i) volatility – 79%, (ii) range of implied fair value of the Series F redeemable convertible preferred stock – $2.19 to $2.85, (iii) time to liquidity – 8 months to 5 years, and (iv) range of probabilities of liquidity event outcomes – 2% to 31%. The warrants were valued again at April 10, 2013, just prior to the Company’s IPO, using a Black-Scholes valuation model. The key unobservable inputs used in determination of the fair value at that time were (i) volatility – 79%, (ii) fair value of the Series F redeemable convertible preferred stock – $3.94, (iii) expected life – 2.5 years, (iv) risk-free interest rate – 0.24%, and (v) dividend yield – 0%. As the warrants for Series F redeemable convertible preferred stock converted to warrants for common stock upon the IPO, no future valuations are necessary.
	There was no material re-measurement to fair value of financial assets and liabilities that are not measured at fair value on a recurring basis.
	Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:
						Fair Value Measurements at
						31-Dec-13
			December 31,			Quoted Prices in		Significant Other		Significant
			2013			Active Markets		Observable Inputs		Unobservable Inputs
						for Identical Assets		(Level 2)		(Level 3)
						(Level 1)
			(in thousands)
	Cash equivalents		$	107,349		$	107,349	$	—	$	—
						Fair Value Measurements at
						31-Dec-12
			December 31,			Quoted Prices in		Significant Other		Significant
			2012			Active Markets		Observable Inputs		Unobservable Inputs
						for Identical Assets		(Level 2)		(Level 3)
						(Level 1)
			(in thousands)
	Cash equivalents		$	17,687		$	16,381	$	1,306	$	—
	Short-term investments			9,849			—		9,849		—
	Redeemable convertible preferred stock warrant liability			7,512			—		—		7,512
	Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):
			Fair Value
			Measurements
			(Level 3)
			(in thousands)
	Redeemable Convertible Preferred Stock Warrant Liability
	Balance at January 1, 2012		$	6,491
	Issuance			174
	Fair value increase recorded in other expense			847
	Fair value at December 31, 2012			7,512
	Fair value increase recorded in other expense			6,590
	Reclassification of warrant liability to additional paid-in capital			(14,102	)
	Fair value at December 31, 2013		$	—
	Prepaid and Other Current Assets
	Prepaid and other current assets consist of the following:
			31-Dec-13			31-Dec-12
		(in thousands)
Prepaid development expenses		$	2,433		$	486
Deferred public offering costs			—			273
Other prepaid and other current assets			332			224
		$	2,765		$	983
Property and Equipment
Property and equipment are stated at cost, less accumulated depreciation. Depreciation is determined on a straight-line basis over the estimated useful lives of the assets, which generally range from three to five years. Leasehold improvements are amortized over the shorter of the useful life of the asset or the term of the related lease. Maintenance and repairs are charged against expense as incurred.
Impairment of Long-Lived Assets
The Company evaluates long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If the estimated future cash flows (undiscounted and without interest charges) from the use of an asset are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. To date, no such write-downs have occurred.
Deferred Public Offering Costs
Deferred public offering costs totaling $0.3 million at December 31, 2012 are included in prepaid and other current assets. These costs represent legal and accounting costs related to the Company’s efforts to raise capital through an IPO. At the completion of the IPO in April 2013, these costs were reclassified to additional paid-in capital as a reduction of the IPO proceeds.
Deferred Rent
The Company recognizes rent expense on a straight-line basis over the non-cancelable term of its operating lease and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. The Company also records landlord-funded lease incentives, such as reimbursable leasehold improvements, as a deferred rent liability, which is amortized as a reduction of rent expense over the non-cancelable term of its operating lease.
Accrued Liabilities
Accrued liabilities consist of the following:
		31-Dec-13			31-Dec-12
		(in thousands)
Accrued compensation		$	1,779		$	560
Accrued development expenses			350			98
Other accrued liabilities			291			248
		$	2,420		$	906
Redeemable Convertible Preferred Stock Warrant Liability
Freestanding warrants for shares that are either putable or redeemable are classified as liabilities on the balance sheet at fair value. As further discussed in Note 6, the preferred stock underlying certain warrants was redeemable in certain circumstances, and as such the freestanding warrants that are related to the purchase of the Company’s Series F preferred stock were liabilities that should be recorded at the estimated fair value. At the end of each reporting period, changes in the estimated fair value during the period are recorded in other income.
Redeemable Convertible Preferred Stock
The Company classified its redeemable convertible preferred stock, for which the Company did not control the redemption, outside of permanent equity. The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any offering costs, and the carrying value was adjusted to the redemption value at the end of each reporting period. These adjustments were effected through charges against additional paid-in capital and accumulated deficit.
Revenue Recognition
The Company’s revenues generally consist of (i) contract and grant revenues – revenues generated under federal contracts and other awarded grants, and (ii) collaboration and licensing revenues – revenues related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenues are recognized when the following criteria are met: (1) persuasive evidence that an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured.
For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively.
Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of the Company’s substantive performance obligations. If the Company does not have substantive performance obligations, the Company recognizes non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation.
Milestone payments are recognized when earned, provided that (i) the milestone event is substantive; (ii) there is no ongoing performance obligation related to the achievement of the milestone earned; and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement; and the related risk associated with the achievement of the milestone. Contingent based event payments the Company may receive under a license or collaboration agreement will be recognized when received.
For the years ended December 31, 2013, 2012 and 2011, contract and grant revenue consisted only of revenue from the BARDA contract as there was no grant revenue. The Company recognizes contract and grant revenue as qualifying research activities are conducted based on invoices received from the Company’s vendors. Changes in fringe and indirect rates are recognized as a change in estimate in the period such rate changes are approved by BARDA.
Clinical Trial Accruals
As part of the process of preparing financial statements, the Company is required to estimate its expenses resulting from its obligation under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate clinical trial expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of trials, or the services completed. During the course of a clinical trial, the Company adjusts its rate of clinical trial expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through December 31, 2013, there had been no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. The Company’s clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.
Research and Development
Major components of research and development costs include cash compensation, stock based compensation, pre-clinical studies, clinical trial and related clinical manufacturing, drug development, materials and supplies, legal, regulatory compliance, and fees paid to consultants and other entities that conduct certain research and development activities on the Company’s behalf. Research and development costs, including upfront fees and milestones paid to contract research organizations, are expensed as goods as received or services rendered. Costs incurred in connection with clinical trial activities for which the underlying nature of the activities themselves do not directly relate to active research and development, such as costs incurred for market research and focus groups linked to clinical strategy as well as costs to build the Company’s brand, are not included in research and development costs but are reflected as general and administrative costs.
Interest Expense, Net
Interest expense, net includes interest earned on short-term investments, interest incurred on loans payable, the amortization of deferred financing costs related to fees paid to attorneys and other non-lender entities in order to acquire debt, and the amortization of debt discount related to fees paid to the lender in order to acquire debt.
Income Taxes
Deferred tax assets and liabilities are determined based on differences between the financial and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are established when the Company determines that it is more likely than not that some portion of a deferred tax asset will not be realized. The Company has incurred operating losses from April 7, 2000 (inception) through December 31, 2013, and therefore has not recorded any current provision for income taxes.
Additionally, the Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefit recognized in the financial statements for a particular tax position is based on the largest benefit that is more likely than not to be realized upon settlement. Accordingly, the Company establishes reserves for uncertain tax positions.
Share-Based Compensation
The Company measures and recognizes compensation expense for all share-based payment awards made to employees and directors, including employee stock options, based on estimated fair values. The fair value of share-based awards is estimated on the grant date using the Black-Scholes valuation model. The value of the portion of the award that is ultimately expected to vest is recorded as expense over the requisite service periods.
The Company also accounts for equity instruments issued to non-employees using a fair value approach. The Company values equity instruments, stock options and warrants granted to lenders and consultants using the Black-Scholes valuation model. The measurement of non-employee share-based compensation is subject to periodic adjustments as the underlying equity instruments vest and is recognized as an expense over the term of the related financing or the period over which services are received.
Basic and Dilutive Net Loss Per Share of Common Stock
Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of converting redeemable convertible preferred stock, warrants to purchase redeemable convertible preferred stock and common stock, restricted stock and options. 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 redeemable convertible preferred stock and warrants to purchase redeemable convertible preferred stock, and options outstanding during the period calculated in accordance with the treasury stock method, but are excluded if their effect is anti-dilutive. Because the impact of these items is anti-dilutive during the periods of net loss, there was no difference between basic and diluted loss per share of common stock at December 31, 2013, 2012 and 2011.
The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of converting redeemable convertible preferred stock, warrants to purchase convertible preferred stock and options to purchase common stock, as the impact of such items are anti-dilutive during periods of net loss. Shares excluded from the calculations were 4,773,213,  11,259,579 and 11,034,134 for the years ended December 31, 2013, 2012 and 2011, respectively.
Segments
The Company operates in only one segment. The chief operating decision-maker, who is the Company’s Chief Executive Officer, and management use cash flows as the primary measure to manage the business and do not segment the business for internal reporting or decision making.
Impact of Recently Issued Accounting Standards
In July of 2013, the Financial Accounting Standards Board issued ASU 2013-11, “Income Taxes, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (a consensus of the FASB Emerging Issues Taskforce)” ("ASU 2013-11"). Beginning January 1, 2014, the effective date of this regulation, the Company will adopt the provisions of ASU 2013-11 related to presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. Adoption of ASU 2013-11 is not expected to have a material impact to the financial statements.

Investments

Investments	12 Months Ended
	Dec. 31, 2013
Investments [Abstract]	'
Investments	'
	2. Investments
	The Company had no short or long-term investments at December 31, 2013.
	The following table summarizes available-for-sale securities as of December 31, 2012:
		Amortized Cost		Gross Unrealized		Gross Unrealized			Estimated
				Gains		Losses			Fair Value
		(in thousands)
	Corporate bonds	$	8,353	$	—	$	(2	)	$	8,351
	Commercial paper		1,498		—		—			1,498
	Total	$	9,851	$	—	$	(2	)	$	9,849
	All of the Company’s investments as of December 31, 2012 had maturities of one year or less.

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2013
Property and Equipment [Abstract]	'
Property and Equipment	'
	3. Property and Equipment
	Property and equipment consist of the following:
		31-Dec-13			31-Dec-12
		(in thousands)
	Lab equipment	$	873		$	958
	Leasehold improvements		78			78
	Computer equipment		324			393
	Office furniture and equipment		222			212
			1,497			1,641
	Less accumulated depreciation		(1,159	)		(1,234	)
		$	338		$	407

Loan_Payable

Loan Payable	12 Months Ended
	Dec. 31, 2013
Loan Payable [Abstract]	'
Loan Payable	'
	4. Loan Payable
	On January 27, 2012, the Company entered into a Loan and Security Agreement (LSA) with Silicon Valley Bank (SVB) and MidCap Financial SBIC, LP (MidCap) allowing for borrowings up to $15.0 million, split between a first tranche of $3.0 million borrowed at the time of the agreement, and a second tranche of up to $12.0 million that would be available to be drawn by December 31, 2012 upon meeting one of three stated financial and/or operational goals.
	The first tranche was used to repay the remaining principal balance outstanding of $2.6 million under a previous loan. This repayment was deemed a modification of debt and therefore the remaining related deferred financing costs totaling $0.1 million remained in deferred financing costs and are being amortized over the term of the LSA through interest expense. The first tranche has an interest-only period of twelve months followed by a 30-month principal and interest amortization period with interest being charged at 8.25% per year for the full period of the LSA.
	The Company met one of the financial and/or operational goals mentioned above and, in September 2012, the remaining $12.0 million was borrowed in the second tranche. The second tranche has a six-month interest-only period followed by a 32 month principal and interest amortization period with interest being charged at the same rate as the first tranche. There are certain fees in accordance with the LSA which are being recorded as discounts or other long and short-term liabilities depending on the nature of the fees. The fees are being accreted through interest expense. Approximately $0.1 million and $0.1 million was included in interest expense for the years ended December 31, 2013 and 2012, respectively.
	Concurrently with entering into the LSA, the Company also granted SVB a warrant to purchase shares of Series F preferred stock at a price of $2.045 per share equal to 2% of the aggregate amount of the advances made to the Company pursuant to the LSA, divided by the exercise price. In relation to the first tranche, the warrant became exercisable to purchase an aggregate of 29,340 shares of Series F preferred stock, and in relation to the second tranche, the warrant became exercisable to purchase an additional 117,360 shares of Series F preferred stock. As discussed in Note 1, the warrant is classified as a liability and is required to be measured at fair value. Therefore, the warrant was recorded as a debt discount at its fair value at the time of grant and accreted over the life of the LSA using the effective interest method. Upon the completion of the Company’s IPO, this warrant was converted into a warrant to purchase 41,323 shares of common stock at an exercise price equal to $7.26. In May 2013, SVB exercised the warrant in full and it is no longer outstanding.
	The future payments under the LSA are as follows (in thousands):
	Years ending December 31,
	2014	$	6,322
	2015		4,508
			10,830
	Less: amount representing interest		(780	)
	Total payments under LSA	$	10,050

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies [Abstract]	'
Commitments and Contingencies	'
	5. Commitments and Contingencies
	Leases
	The Company leases its facilities and certain office equipment under long-term non-cancelable operating leases that expire at various dates through 2018.  The Company has the following minimum payments under noncancelable operating lease obligations that existed at December 31, 2013 (in thousands):
	Years ending December 31,
	2014	$	331
	2015		275
	2016		245
	2017		243
	2018		41
		$	1,135
	Rent expense under non-cancelable operating leases and other month-to-month equipment rental agreements, including common area maintenance fees, totaled approximately $0.5 million and $0.4 million for the years ended December 31, 2013 and 2012, respectively.
	Significance of Revenue Source
	The Company is the recipient of federal research contract funds from BARDA. Periodic audits are required under the grant and contract agreements and certain costs may be questioned as appropriate under the agreements. Management believes that such amounts in the current year, if any, are not significant. Accordingly, no provision for refundable amounts under the agreements has been made as of December 31, 2013 and 2012.

Redeemable_Convertible_Preferr

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2013
Redeemable Convertible Preferred Stock [Abstract]	'
Redeemable Convertible Preferred Stock	'
	6. Redeemable Convertible Preferred Stock
	In February 2011, the Company issued 22,004,895 shares of $0.001 par value Series F redeemable convertible preferred stock at $2.045 per share and warrants to purchase an aggregate of 5,501,215 shares of Series F redeemable convertible preferred stock at an exercise price of $2.045 per share for proceeds of $45.0 million, less issuance costs of $0.2 million. Upon the completion of the Company’s IPO, these warrants were converted into warrants to purchase an aggregate of 1,549,628 shares of common stock at an exercise price of $7.26 per share. The warrants are exercisable at any time and expire on February 4, 2018.
	In January 2012, the Company issued a warrant to SVB to purchase a number of shares of Series F redeemable convertible preferred stock at an exercise price of $2.045 per share equal to 2% of the aggregate amount of the advances made to the Company pursuant to the LSA, divided by the exercise price. Following the first and second tranches of the LSA, the warrant was exercisable to purchase an aggregate of 146,700 shares of Series F redeemable convertible preferred stock. Upon the completion of the Company’s IPO, this warrant was converted into a warrant to purchase 41,323 shares of common stock at an exercise price of $7.26 per share. In May 2013, SVB exercised the warrant in full and it is no longer outstanding.
	The following table summarizes the authorized, issued and outstanding shares of redeemable convertible preferred stock as of December 31, 2012:
		Authorized				Issued and
		Shares				Outstanding Shares
	Series A		800,000				800,000
	Series B		2,233,879				2,233,879
	Series B-1		2,054,333				2,033,333
	Series C		5,141,690				5,141,690
	Series D		11,354,526				11,295,846
	Series E		7,894,871				7,894,871
	Series F		40,200,000				22,004,895
	Total Shares		69,679,299				51,404,514
	Upon the completion of the Company’s IPO in April 2013, the Company’s outstanding shares of redeemable convertible preferred stock and dividends accrued on Series F redeemable convertible preferred stock were automatically converted into an aggregate of 15,556,091 shares of common stock.
	Warrants
	The following warrants for the purchase of preferred stock were issued, outstanding and exercisable at December 31, 2012:
	Class	Date		Shares				Price Per Share		Expiration
	Series B-1	5-Nov-03			21,000			$	1.500	Nov-13
	Series D	24-Nov-08			58,680			$	2.045	Nov-18
	Series F	7-Feb-11			5,501,215			$	2.045	Feb-18
	Series F	27-Jan-12			146,700			$	2.045	Jan-22
	As discussed in Note 1, the warrants exercisable for the Company’s Series F preferred stock were classified as a liability and were required to be measured at fair value. Therefore, such warrants were recorded at the full fair value with the Company’s Series F preferred stock being recorded at the residual value at the time of issuance. At each reporting date prior to the Company’s IPO, the warrants exercisable for the Company’s Series F preferred stock were recorded to fair value which was charged to other income.  For the years ended December 31, 2013 and 2012, the Company recorded expense of $6.4 million and $0.8 million, respectively, related to the valuation of the warrants. These amounts, coupled with the fair valuation of the warrants issued in relation to the Company’s LSA (see note 4), total to the fair value adjustments to warrant liability amount per the statements of operations and comprehensive loss.
	Upon the completion of the Company’s IPO, all outstanding warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase 1,613,395 shares of common stock and are no longer required to be measured at fair value. On April 16, 2013, a warrant was exercised to purchase 211,783 shares of the Company’s common stock. The Company received proceeds of $1.5 million in connection with such exercise. On May 24, 2013, a warrant was net exercised which resulted in the issuance of 37,600 shares of the Company’s common stock. On November 5, 2013, a warrant was net exercised which resulted in the issuance of 3,906 shares of the Company’s common stock.
	The following warrants for the purchase of common stock were issued, outstanding and exercisable at December 31, 2013:
	Class	Date		Shares				Price Per Share		Expiration
	Common	7-Feb-11			1,337,845			$	7.26	Feb-18

Stockholders_Equity_Deficit

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity (Deficit) [Abstract]	'
Stockholders' Equity (Deficit)	'
	7. Stockholders’ Equity (Deficit)
	Common Stock
	The Company’s common stock consists of 200.0 million and 89.7 million authorized shares at December 31, 2013 and December 31, 2012, respectively, and 26.7 million and 1.5 million shares issued and outstanding at December 31, 2013 and December 31, 2012, respectively.
	Shares Reserved for Future Issuance
	The following shares of common stock reserved for future issuances:
		31-Dec-13				31-Dec-12
	Conversion of preferred stock and preferred stock warrants		—				16,093,483
	Exercise of common stock warrants		1,337,845				—
	Stock options issued and outstanding		1,946,823				2,593,423
	Restricted Stock units outstanding		-				43,199
	Authorized for future purchases under the 2013 Employee Stock Purchase Plan		704,225				—
	Authorized for future grants under the 2013 Equity Incentive Plan		1,681,932				—
	Authorized for future grants under the 2012 Equity Incentive Plan		—				427,933
			5,670,825				19,158,038
	Stock Options
	In connection with the Company’s IPO, the Company adopted the 2013 Equity Incentive Plan (the 2013 Plan). The 2013 Plan provides for the grant of incentive stock options (ISOs), nonstatutory stock options (NSOs), stock appreciation rights, restricted stock awards, restricted stock unit (RSU) awards, performance-based stock awards, and other forms of equity compensation (collectively, stock awards), all of which may be granted to employees, including officers, non-employee directors and consultants of the Company and its affiliates. Additionally, the 2013 Plan provides for the grant of performance cash awards. ISOs may be granted only to employees. All other awards may be granted to employees, including officers, and to non-employee directors and consultants. Initially, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2013 Plan is the sum of (i) 1,408,450 shares, plus (ii) 244,717 shares, which was the number of shares reserved for issuance under the Company’s 2012 Equity Incentive Plan (the 2012 Plan) at the time the 2013 Plan became effective, plus (iii) any shares subject to outstanding stock options or other stock awards that would have otherwise returned to the 2012 Plan (such as upon the expiration or termination of a stock award prior to vesting). Additionally, the number of shares of common stock reserved for issuance under the 2013 Plan will automatically increase on January 1 of each year, beginning on January 1, 2014 and continuing through and including January 1, 2023, by 2.5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. The maximum number of shares that may be issued upon the exercise of ISOs under the 2013 Plan is 2,816,901 shares. Following the effectiveness of the 2013 Plan in April 2013, no further grants were made under the 2012 Plan.
	The 2013 Plan has an “early exercise” provision under which options to purchase common stock may be exercised prior to being fully vested; however, the shares issued for options exercised under the “early exercise” provision continue to vest under the same terms as the underlying exercised option. Upon termination of an employee prior to the vesting of such shares, the Company can either repurchase the unvested shares or let the repurchase right expire.
	The Company estimates the fair value of its share-based awards to employees, directors and consultants using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of highly complex and subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the Company’s limited operating history and historical and implied volatility data, the Company has based its estimates of expected volatility on a blend of Company specific historical data and a group of similar public traded companies. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, positions within the industry, and with historical share price information sufficient to meet the expected life of its stock options. For employee stock options the Company uses the “simplified” method for estimating expected life, whereby, the expected life equals the arithmetic average of the vesting term and the original contractual term of the option due to its lack of sufficient historical data. The expected term for share-based compensation granted to non-employees is the contractual life. The risk-free interest rates for the periods within the expected life of the option are based on the U.S. Treasury instrument with a life that is similar to the expected life of the option grant. The Company has never paid, and does not expect to pay, dividends in the foreseeable future. The following table illustrates the assumptions for the Black-Scholes model used in determining the fair value of the options granted.
		Employees
		Year Ended December 31,
		2013				2012				2011
	Dividend yield		0.00	%			0.00	%			0.00	%
	Weighted-average risk-free interest rate		1.49	%			0.86	%			2.85	%
	Volatility		76.40	%			80.55	%			82.00	%
	Expected term (in years)		6.1				6.0				7.0
	Weighted-average fair value per option	$	2.52			$	1.93			$	1.74
				Non-Employees
				Year Ended December 31,
		2013						2012				2011
	Dividend yield				0.00	%			0.00	%			0.00	%
	Weighted-average risk-free interest rate				1.30	%			0.78	%			0.40	%
	Volatility				79.69	%			81.77	%			77.80	%
	Expected term (in years)				6.2				5.8				2.7
	Weighted-average fair value per option		$		5.01			$	3.48			$	3.38
	The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised. For the years ended December 31, 2013, 2012 and 2011, the Company applied a forfeiture rate based on the Company’s historical forfeitures.
	In February 2013, the Company’s board of directors adopted the 2013 Employee Stock Purchase Plan (ESPP), which was subsequently ratified by stockholders and became effective in April 2013. The purpose of the ESPP is to retain the services of new employees and secure the services of new and existing employees while providing incentives for such individuals to exert maximum efforts toward the Company’s success and that of its affiliates. The ESPP initially authorized the issuance of 704,225 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of its designated affiliates. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2014 through January 1, 2023 by the least of (a) 1% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (b) 422,535 shares, or (c) a number determined by the Company’s board of directors that is less than (a) and (b). The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code of 1986. As of the date hereof, no shares of common stock have been purchased under the ESPP.
	A summary of activity related to the Company’s stock options is as follows:
		Number of Options				Weighted-Average				Weighted-Average
		Outstanding				Exercise Price				Remaining Contractual
										Life (in Years)
	Balance, January 1, 2012		2,631,415			$	2.24				7.69
	Granted		382,167				3.24				—
	Exercised		(16,530	)			0.82				—
	Expired or Canceled		(102,228	)			2.63				—
	Forfeited		(301,401	)			1.69				—
	Balance, December 31, 2012		2,593,423			$	2.45				7.36
	Granted		292,906				10.62				—
	Exercised		(801,049	)			2.43				—
	Expired or Canceled		(2,816	)			1.57				—
	Forfeited		(135,641	)			4.55				—
	Balance, December 31, 2013		1,946,823			$	3.54				7.03
	Exercisable at December 31, 2013		1,266,070			$	2.32				6.21
	Vested or expected to vest at December 31, 2013		1,952,222			$	3.5				7.02
	At December 31, 2013, the aggregate intrinsic value of options outstanding and exercisable was $16.2 million. The total intrinsic value of options exercised was $12.4 million, $18,000 and $16,000 for the years ended December 31, 2013, 2012 and 2011, respectively.
	In 2012, the Company modified option grants for four individuals. Three of the modifications extended the term to exercise the option resulting in $30,000 in additional compensation expense. One option was modified to continue vesting after the participant’s termination and to extend the time to exercise such option resulting in additional compensation expense of $0.3 million.
	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. The fair value of options vested and share-based compensation expense recognized are as follows:
		Year Ended December 31,
		2013				2012				2011
		(in thousands)
	Research and development:
	Employee	$	537			$	336			$	315
	Non-employee		67				80				—
	General and administrative:
Employee		458				921				651
Non-employee		82				59				—
	$	1,144			$	1,396			$	966
Cash received from option exercises under all share-based payment arrangements for 2013 and 2012, was $1.9 million and $14,000, respectively. There was no actual tax benefit realized for the tax deductions from option exercises of the share-based payment arrangements during 2013 or 2012.
As of December 31, 2013, there was approximately $2.5 million of total unrecognized compensation cost related to non-vested share-based compensation arrangements granted under the 2013 Plan. That compensation cost is expected to be recognized over a weighted-average period of approximately 2.54 years.
The Company continues to account for stock options issued to non-employees using a fair value approach. The compensation costs of these arrangements are subject to re-measurement over the vesting terms as earned. Compensation cost for performance-based awards is recognized when it is probable that the performance criteria will be met.
Restricted Stock Units
In 2013 and 2012, the Company issued RSUs to certain employees which vest based on specific performance criteria. By their terms, the RSUs became immediately vested upon the effective date of the registration statement for the Company’s common stock in connection with the IPO, subject to the continuous service with the Company at the vesting event. When vested, the RSU represented the right to be issued the number of shares of the Company’s common stock that is equal to the number of RSUs granted.
A summary of activity related to the Company’s RSUs is as follows:
	Number of Restricted
	Stock Units Outstanding
Balance, December 31, 2012		43,199
Granted		59,348
Share issuance		(102,547	)
Balance, December 31, 2013		—
In April 2013, $1.9 million in compensation expense had been recorded in connection with the RSUs as the performance criterion was met upon the completion of the Company’s IPO. In November 2013, the requisite number of shares of common stock were issued in relation to the RSUs.
Fair Value Estimate
Prior to the Company’s IPO, the Company was required to estimate the fair value of the common stock underlying stock-based awards when performing the fair value calculations with the Black-Scholes option-pricing model. The fair value of the common stock underlying stock-based awards was determined on each grant date by the Company’s board of directors, with input from management. All options to purchase shares of common stock are intended to be granted with an exercise price per share no less than the fair value per share of common stock underlying those options on the date of grant, based on the information known on the date of grant.
The Company was privately held with no active public market for its common stock. Therefore, management had for financial reporting purposes periodically determined the estimated per share fair value of the Company’s common stock and redeemable convertible preferred stock at various dates using contemporaneous valuations consistent with the American Institute of Certified Public Accountants Practice Aid, “Valuation of Privately-Held Company Equity Securities Issued as Compensation,” also known as the Practice Aid. These valuations were performed with the assistance of a third-party valuation specialist. The Company performed these contemporaneous valuations as of February 15, 2011, December 31, 2011, and September 30, 2012 and December 31, 2012. In conducting these contemporaneous valuations, management considered all objective and subjective factors that it believed to be relevant in each valuation conducted, including management’s best estimate of the Company’s business condition, prospects and operating performance at each valuation date. Within the contemporaneous valuations performed, a range of factors, assumptions and methodologies were used. The significant factors included external market conditions affecting the biotechnology industry, trends within the biotechnology industry, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of the preferred stock relative to common stock at the time of each grant, the results of operations, financial position, status of research and development efforts, stage of development and business strategy, the lack of an active public market for the common and preferred stock, and the likelihood of achieving a liquidity event such as an IPO or sale of the Company in light of prevailing market conditions.
The dates of the Company’s contemporaneous valuations had not always coincided with the dates of its stock-based compensation grants. In such instances, management’s estimates had been based on the most recent contemporaneous valuation of the Company’s shares of common stock and its assessment of additional objective and subjective factors management believed were relevant and which may have changed from the date of the most recent contemporaneous valuation through the date of the grant. In addition, the Company performed retrospective valuations as of certain key option grant dates using similar methodologies as were used in the contemporaneous valuations. As a result, the Company concluded certain options granted in 2012 had reassessed values different from the grant date. The reassessed values were used to determine stock compensation expense for the year ended December 31, 2012.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Taxes [Abstract]	'
Income Taxes	'
	8. Income Taxes
	No income tax expense or benefit has been recorded for the years ended December 31, 2013 or December 31, 2012. This is due to the establishment of a valuation allowance against the deferred tax assets generated during those periods. At December 31, 2013, the Company has concluded that it is more likely than not that the Company may not realize the benefit of its deferred tax assets due to its history of losses. Accordingly, the net deferred tax assets have been fully reserved.
	A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2013, 2012, and 2011:
		2013							2012						2011
		Amount			% of Pretax Earnings				Amount			% of Pretax Earnings			Amount			% of Pretax Earnings
		(in thousands)
	Income tax benefit at statutory rate	$	(12,392	)		34	%		$	(1,499	)		34	%	$	(8,700	)		34	%
	State income taxes		(852	)		2.3	%			(100	)		2.3	%		(1,164	)		4.6	%
	Research and development credits		(2,265	)		6.2	%			—			0	%		(1,171	)		4.6	%
	Permanent items		3,060			(8.4	)%			868			(19.7	)%		964			(3.8	)%
	Provision to return adjustments		320			(0.9	)%			2			0	%		12			0	%
	Effect of change in state tax rate		-1			0	%			609			(13.9	)%		630			(2.5	)%
	Increase in unrecognized tax benefits		566			(1.5	)%			—			0	%		314			(1.2	)%
	Valuation allowance		11,564			(31.7	)%			120			(2.7	)%		9,115			(35.7	)%
	Net benefit	$	—			0	%		$	—			0	%	$	—			0	%
	The components of deferred tax assets and liabilities at December 31, 2013 and 2012 are as follows:
		December 31,
		2013					2012
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$		40,721			$	31,431
	Research and development expenses			127				34
	Capitalized Section 174 expenses			69				80
	Research and development credits			2,640				941
	Accrued bonuses			405				54
	Other			497				445
	Total gross deferred tax assets			44,459				32,985
	Valuation allowance			(44,405	)			(32,841			)
				54				144
	Deferred tax liabilities:
	Other			(54	)			(144			)
	Total deferred tax liabilities			(54	)			(144			)
	Net deferred tax assets	$		—			$	—
	At December 31, 2013, the Company has net operating loss carryforwards for federal and state tax purposes of approximately $117.5 million and $106 million, respectively. At December 31, 2012, the Company has net operating loss carryforwards for federal and state purposes of approximately $83.6 million and $65.8 million, respectively. The federal losses begin to expire in 2020 and the state losses begin to expire in 2023. The Company’s federal and state net operating loss carryforwards include approximately $7.3 million of excess tax benefits related to deductions from the exercise of stock options. The tax benefit of these deductions has not been recognized in deferred tax assets. If utilized, the benefits from these deductions will be recorded as adjustments to additional paid-in capital. In addition, the Company has tax credit carryforwards for federal tax purposes of approximately $3.5 million as of December 31, 2013, which begin to expire in 2022. The future utilization of net operating loss and tax credit carryforwards may be limited due to changes in ownership. Management has recorded a valuation allowance for all of the deferred tax assets due to the uncertainty of future taxable income.
	The research and development credit, which had previously expired on December 31, 2011, was reinstated as part of the American Taxpayer Relief Act of 2012 enacted on January 2, 2013. This legislation retroactively reinstated and extended the credit from the previous expiration date through December 31, 2013. As a result, the Company adjusted its deferred tax assets in 2013 for the 2013 and 2012 research and development credits, which resulted in an increase to the deferred tax assets and a corresponding increase to the valuation allowance of $1.2 million and $1.1 million, respectively.
	In general, if the Company experiences a greater than 50% aggregate change in ownership of certain significant stockholders over a three-year period (a Section 382 ownership change), utilization of its pre-change net operating loss carryforwards is subject to an annual limitation under Section 382 of the Internal Revenue Code (and similar state laws). The annual limitation generally is determined by multiplying the value of the Company’s stock at the time of such ownership change (subject to certain adjustments) by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the net operating loss carryforwards before utilization and may be substantial. The ability of the Company to use its net operating loss carryforwards may be limited or lost if the Company experienced one or more Section 382 ownership changes in connection with past offerings of its stock or as a result of future changes in its stock ownership. Losses from a specific period may be subject to multiple limitations, and would generally be limited by the lowest of those limitations.
	The Company has determined that a Section 382 ownership change occurred in 2002, and as such, losses incurred prior to that date are subject to an annual limitation of at least $64,000. Additionally, the Company has determined that a Section 382 ownership change occurred in 2007, and as such, losses incurred prior to that date are subject to an annual limitation of at least $762,000. The Company evaluated Section 382 ownership changes subsequent to 2007 through 2013 and concluded that a Section 382 ownership change occurred in 2013 as a result of the initial public offering, the Company’s most recent private placement and other transactions that have occurred since 2007. As such, losses incurred prior to that date are subject to an annual limitation of at least $6.7 million.
	The Company had gross unrecognized tax benefits of approximately $0.3 million as of January 1, 2013. As the 2012 R&D tax credit was not yet enacted into current law, no R&D credit was reflected on the 2012 provision.  As a result, the Company recognized an increase in the unrecognized tax benefit associated with the federal R&D credit carryover in the current year related to the periods ending December 31, 2012 and 2013.  As of December 31, 2013, the total gross unrecognized tax benefits were approximately $0.9 million and of this total, none would reduce the Company’s effective tax rate if recognized. The Company does not anticipate a significant change in total unrecognized tax benefits or the Company’s effective tax rate due to the settlement of audits or the expiration of statutes of limitations within the next twelve months. Furthermore, the Company does not expect any cash settlement with the taxing authorities as a result of these unrecognized tax benefits as the Company has sufficient unutilized carryforward attributes to offset the tax impact of these adjustments.
	The Company has determined that there may be a future limitation on the Company’s ability to utilize its entire federal R&D credit carryover. Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the year ended December 31, 2013, as follows (in thousands):
	Balance at December 31, 2011	$	314
	Increases related to 2012		—
	Balance at December 31, 2012		314
	Increase related to 2013		297
	Increase related to prior periods		269
	Balance at December 31, 2013	$	880
	The Company has determined that it had no other material uncertain tax benefits for the year ended December 31, 2013. As of January 1, 2014, due to the carry forward of unutilized net operating losses and research and development credits, the Company is subject to U.S. Federal and state income tax examinations for the tax years 2000 through 2013. The Company recognizes accrued interest related to unrecognized tax benefits in interest expense and penalties in operating expense. No amounts were accrued for the payment of interest and penalties at January 1, 2014.

Significant_Agreements

Significant Agreements	12 Months Ended
	Dec. 31, 2013
Significant Agreements [Abstract]	'
Significant Agreements	'
	9. 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 and CMX157. The license agreement was amended in September 2002 in order to expand the scope of the license and again in December 2010 in order to modify certain financial terms. The agreement was amended a third time in September 2011 to add additional patents related to certain metabolically stable lipid-conjugate compounds. A fourth amendment was executed in July 2012 to alter the rights and obligations of the parties in light of the Company’s current business plans. As partial consideration for the rights granted to the Company under the license agreement, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights. In connection with the development and commercialization of brincidofovir and CMX157, the Company could be required to pay UC up to an aggregate of $3.4 million in milestone payments, assuming the achievement of all applicable milestone events under the license agreement.
	Under the license agreement, the Company is permitted to research, develop, manufacture and commercialize products utilizing the UC Patent Rights for all human and veterinary uses, and to sublicense such rights. UC retained the right, on behalf of itself and other non-profit institutions, to use the UC Patent Rights for educational and research purposes and to publish information about the UC Patent Rights.
	In consideration for the rights granted under the license agreement, the Company has issued UC an aggregate of 64,788 shares of common stock. As additional consideration, the Company is required to pay certain cash milestone payments in connection with the development and commercialization of compounds that are covered by the UC Patent Rights, plus certain annual fees to maintain such patents until the Company commercializes a product utilizing UC Patent Rights. In addition, upon commercialization of any product utilizing the UC Patent Rights (which would include the commercialization of brincidofovir or CMX157), the Company will be required to pay low single digit royalties on net sales of such product.
	In the event the Company sublicenses a UC Patent Right the Company is obligated to pay to UC a fee, which amount will vary depending upon the size of any upfront payment 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 or CMX157, the fee payable to UC will not exceed 5% and 10% of the sublicense fee, respectively. In addition, the Company will also be required to pay to UC a low single digit sublicense royalty on net sales of products that use the sublicensed UC Patent Rights, but in no event will the Company be required to pay more than 50% of the royalties it receives in connection with the relevant sublicense. Any such royalty payment will be reduced by other payments the Company is required to make to third parties until a minimum royalty has been reached.
	As a result of meeting certain milestones and sublicense fees related to this license agreement, the Company recognized expenses of $0.9 million for the year ended December 31, 2012. The Company did not recognize expenses under this license agreement for the year ended December 31, 2013.
	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. The contract has been amended several times; most recently on December 10, 2013 to increase the option segment award to $5.3 million.
	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 of approximately one year each, 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 first option segment of the contract during which the Company may receive up to a total of $5.3 million in expense reimbursement and fees. The term of the first option segment is 12 months and is scheduled to end on May 30, 2014.
	Merck, Sharp & Dohme Corp.
	In July 2012, the Company entered into a collaboration and license agreement granting Merck exclusive worldwide rights to CMX157, the Company’s lipid acyclic nucleoside phosphonate currently being evaluated to treat HIV infection. Under the terms of the agreement, Merck received an exclusive worldwide license for any human use of CMX157 and has agreed to use commercially reasonable efforts to develop and commercialize CMX157 in the United States and at least three major European markets. Following execution of the agreement, the Company received a $17.5 million upfront payment from Merck.
	As additional consideration, the Company is eligible to receive up to a total of $151.0 million in milestone payments if certain development and regulatory milestones are achieved by Merck for products utilizing CMX157, as well as tiered royalties on net sales ranging from high single digits to low double digits, depending upon the volume of sales of each applicable product, if CMX157 is successfully commercialized. Milestone payments are triggered upon the completion of various stages of the regulatory approval process for each of the first two indications for CMX157, with the final milestones reached upon approval in the United States and three major European markets. Royalties for any given product will continue on a country-by-country basis through the later of the expiration of the Company’s patent rights applicable to such product or ten years from the first commercial sale of such product.
	The Company’s participation in the collaboration with Merck, including its involvement in the joint steering committee to monitor the development of CMX157, represents a right and an observation role only, rather than a substantive performance obligation. As such, the Company’s performance in this collaboration relates to the specific transfers in connection with the license which was completed during the same quarter the agreement was entered into. Therefore, the Company recognized the upfront payment during the year ended December 31, 2012.
	The contingent event-based payments that the Company may receive pursuant to the agreement do not meet the definition of a milestone as achievement of the triggering event for such payments is based on the performance of Merck and not the Company. Therefore, the milestone method will not be applied to those payments.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
Selected Quarterly Financial Data (Unaudited)	'
	10. Selected Quarterly Financial Data (Unaudited)
	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2013 and 2012 are as follows (in thousands, except per share data):
		2013 Quarter
		Fourth		Third		Second		First
	Total revenues	$	879	$	912	$	808	$	1,771
	Operating loss		-7,979		-6,436		-7,656		-6,548
	Net loss		-8,174		-6,706		-12,459		-9,107
	Net loss per common share, basic and diluted	$	-0.31	$	-0.26	$	-0.91	$	-22.58
	Weighted average shares outstanding, basic and diluted		26,416,787		25,866,109		23,067,201		1,534,016
		2012 Quarter
		Fourth		Third		Second		First
	Total revenues	$	3,581	$	20,856	$	6,205	$	3,078
	Operating (loss) income		-4,143		11,272		-4,422		-5,490
	Net (loss) income		-4,326		11,142		-4,324		-6,898
	Net (loss) income per common share, basic	$	-3.9	$	6.70	$	-3.44	$	-5.14
	Net (loss) income per common share, diluted	$	-3.9	$	0.11	$	-3.44	$	-5.14
	Weighted average shares outstanding, basic		1,532,633		1,529,442		1,518,753		1,517,465
	Weighted average shares outstanding, diluted		1,532,633		52,933,956		1,518,753		1,517,465
	Net income (loss) per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation. Diluted weighted average shares outstanding are identical to basic weighted average shares outstanding and diluted net loss per common share is identical to basic net loss per common share for all quarters of 2013 and for the first, second and fourth quarters of 2013 because common share equivalents are excluded from the calculations of diluted weighted average shares outstanding for those quarters, as their effect is antidilutive.

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	11. Subsequent Events
	The Company has evaluated subsequent events through the issuance date of these financial statements to ensure that this filing includes appropriate disclosure of events both recognized in the financial statements as of December 31, 2013, and events which occurred subsequently but were not recognized in the financial statements.
	In February 2014, the Company entered into an extension of a current facility lease for the period beginning March 2014 and ending June 2014. Future minimum payments under this extension total $0.1 million.

The_Business_and_Summary_of_Si1

The Business and Summary of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2013
The Business and Summary of Significant Accounting Policies [Abstract]	'
Description of Business	'
	Description of Business
	Chimerix is a biopharmaceutical company dedicated to discovering, developing and commercializing novel, oral antivirals to address unmet medical needs.  The Company was founded in 2000 based on the promise of its proprietary lipid technology to unlock the potential of some of the most potent antivirals by enhancing their antiviral activity and safety profiles in convenient, orally administered dosing regiments.  Based on the Company’s lipid technology, its lead compound, brincidofovir (CMX001) is in Phase 3 clinical development, its second compound, CMX157, was licensed to Merck after completing a Phase 1 study and the Company has an active discovery program focusing on viral targets for which no therapies are currently available.
	On March 25, 2013, the Company’s board of directors approved and implemented a 3.55-for-1 reverse stock split of the Company’s outstanding common stock. The reverse stock split resulted in an adjustment to the preferred stock conversion price to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented.
	On April 10, 2013, the Company completed the initial public offering (IPO) of its common stock pursuant to a registration statement on Form S-1. In the IPO, the Company sold an aggregate of 7,320,000 shares of common stock under the registration statement at a public offering price of $14.00 per share. Net proceeds were approximately $93.3 million, after deducting underwriting discounts and commissions of $7.1 million and offering expenses of $2.1 million. Upon the completion of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock and dividends accrued on Series F redeemable convertible preferred stock were converted into 15,556,091 shares of common stock and all outstanding warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase 1,613,395 shares of common stock. On April 16, 2013, the underwriters exercised the full over-allotment option pursuant to which the Company sold an additional 1,098,000 shares at $14.00 per share. Net proceeds from the over-allotment shares were approximately $14.3 million after deducting underwriting discounts and commissions of $1.1 million.
	On October 23, 2013, the Company completed an underwritten secondary public offering of 2,476,995 shares of common stock held by certain of the Company’s existing stockholders. The Company did not issue any shares of common stock and received no proceeds in connection with such offering. The principal purposes of the offering were to facilitate an orderly distribution of shares and to increase the Company’s public float.
	The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The preparation of the Company’s financial statements requires estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the financial statements and accompanying notes. Although these estimates are based on knowledge of current events and actions the Company may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	The Company considers any highly liquid instrument with an original maturity of three months or less at acquisition to be a cash equivalent. Cash equivalents consist of money market accounts.
Investments	'
	Investments
	Investments consist primarily of corporate bonds and commercial paper. The Company invests in high-credit quality investments in accordance with its investment policy which minimizes the probability of loss.
	Available-for-sale securities are carried at fair value as determined by quoted market prices, with the unrealized gains and losses, net of tax, reported as a separate component of stockholders deficit. Realized gains and losses are determined using the specific identification method and transactions are recorded on a settlement date basis in interest income or expense, net. Investments with original maturities beyond three months at the date of purchase and which mature on, or less than twelve months from, the balance sheet date are classified as long-term. The Company periodically reviews available-for-sale securities for other-than-temporary declines in fair value below the cost basis and whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Any such declines in value judged to be other-than-temporary on available-for-sale securities are reported in interest income or expense, net. There were no such declines in value for the years ended December 31, 2013 and 2012.
Concentration of Credit Risk	'
	Concentration of Credit Risk
	Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash, cash equivalents, short-term investments and accounts receivable. The Company is exposed to credit risk, subject to federal deposit insurance, in the event of default by the financial institutions holding its cash and cash equivalents to the extent of amounts recorded on the balance sheets. Accounts receivable represent amounts due from an agency of the federal government.
Accounts Receivable	'
	Accounts Receivable
	Accounts receivable at December 31, 2013 and December 31, 2012 consisted of amounts billed and unbilled under the Company’s contract with the Biomedical Advanced Research and Development Authority (BARDA). Receivables under the BARDA contract are recorded as qualifying research activities as conducted and invoices from the Company’s vendors are received. The Company carries its accounts receivable at cost less an allowance for doubtful accounts. On a periodic basis, the Company evaluates its accounts receivable and establishes an allowance based on its history of collections and write-offs and the current status of all receivables. The Company does not accrue interest on trade receivables. If accounts become uncollectible, they will be written off through a charge to the allowance for doubtful accounts. The Company has not recorded a charge to allowance for doubtful accounts as management believes all receivables are fully collectible.
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	The carrying amounts of certain financial instruments, including accounts receivable, notes receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of such instruments. The carrying amount of borrowings under loans payable approximates its fair value based on the determination that the stated rate on such loans payable is consistent with current interest rates for similar borrowing arrangements available to the Company.
	For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements, in accordance with the fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates and are often calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, fair value measurements cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any calculation technique and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the calculated current or future fair values. The Company utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures.
	The Company groups assets and liabilities at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. An adjustment to the pricing method used within either Level 1 or Level 2 inputs could generate a fair value measurement that effectively falls in a lower level in the hierarchy. These levels are:
		·	Level 1 — Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access.
		·	Level 2 — Valuations based on quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and models for which all significant inputs are observable, either directly or indirectly.
		·	Level 3 — Valuations based on inputs that are unobservable and significant to the overall fair value measurement.
	The determination of where an asset or liability falls in the hierarchy requires significant judgment. The Company evaluates hierarchy disclosures and, based on various factors, it is possible that an asset or liability may be classified differently from period to period. However, the Company expects that changes in classification between levels will be rare.
	The Company has cash equivalents, consisting of money market accounts and commercial paper, whose value is based on using quoted market prices. Accordingly, these securities are classified as Level 1.
	At December 31, 2012, the Company had short-term investments, comprised of corporate bonds and commercial paper, for which quoted prices are not available that were valued using independent pricing models or other model-based valuation techniques such as the present value of future cash flows, adjusted for the security’s credit rating, prepayment assumptions and other factors such as credit loss assumptions. Accordingly, these securities are classified as Level 2.
	The warrants issued for Series F redeemable convertible preferred stock included in the Company’s 2012 financial statements are categorized as Level 3 as there are significant unobservable inputs. The valuation of the warrants at December 31, 2012 reflected a two stage process. Using a contingent claims model in combination with the Company’s Series F financing, which occurred in February 2011, the fair value of total equity and all components of the Company’s capital structure, including the warrants, was determined as of the time of the financing event. Using this value as a starting point, a series of equity values and associated probabilities were calculated using simulation methodologies that incorporate both Monte Carlo and risk neutral frameworks. Based on assessments of expected returns and volatilities consistent with market practice, a distribution of equity values was produced which covered the range of values that an informed market participant might expect. These outcomes were organized into ranges and a probability calculated based on the percent of the total falling into each range. This process created a range of equity values. Using a contingent claims framework, each equity value was allocated to the various components of the capital structure including the warrants. Each warrant value was weighted by its respective probability to determine the final fair value of the warrants as of December 31, 2012. The key unobservable inputs used in the determination of the fair value were (i) volatility – 79%, (ii) range of implied fair value of the Series F redeemable convertible preferred stock – $2.19 to $2.85, (iii) time to liquidity – 8 months to 5 years, and (iv) range of probabilities of liquidity event outcomes – 2% to 31%. The warrants were valued again at April 10, 2013, just prior to the Company’s IPO, using a Black-Scholes valuation model. The key unobservable inputs used in determination of the fair value at that time were (i) volatility – 79%, (ii) fair value of the Series F redeemable convertible preferred stock – $3.94, (iii) expected life – 2.5 years, (iv) risk-free interest rate – 0.24%, and (v) dividend yield – 0%. As the warrants for Series F redeemable convertible preferred stock converted to warrants for common stock upon the IPO, no future valuations are necessary.
	There was no material re-measurement to fair value of financial assets and liabilities that are not measured at fair value on a recurring basis.
	Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:
						Fair Value Measurements at
						31-Dec-13
			December 31,			Quoted Prices in		Significant Other		Significant
			2013			Active Markets		Observable Inputs		Unobservable Inputs
						for Identical Assets		(Level 2)		(Level 3)
						(Level 1)
			(in thousands)
	Cash equivalents		$	107,349		$	107,349	$	—	$	—
						Fair Value Measurements at
						31-Dec-12
			December 31,			Quoted Prices in		Significant Other		Significant
			2012			Active Markets		Observable Inputs		Unobservable Inputs
						for Identical Assets		(Level 2)		(Level 3)
						(Level 1)
			(in thousands)
	Cash equivalents		$	17,687		$	16,381	$	1,306	$	—
	Short-term investments			9,849			—		9,849		—
	Redeemable convertible preferred stock warrant liability			7,512			—		—		7,512
	Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):
			Fair Value
			Measurements
			(Level 3)
			(in thousands)
	Redeemable Convertible Preferred Stock Warrant Liability
	Balance at January 1, 2012		$	6,491
	Issuance			174
	Fair value increase recorded in other expense			847
	Fair value at December 31, 2012			7,512
	Fair value increase recorded in other expense			6,590
	Reclassification of warrant liability to additional paid-in capital			(14,102	)
	Fair value at December 31, 2013		$	—
Property and Equipment	'
	Property and Equipment
	Property and equipment are stated at cost, less accumulated depreciation. Depreciation is determined on a straight-line basis over the estimated useful lives of the assets, which generally range from three to five years. Leasehold improvements are amortized over the shorter of the useful life of the asset or the term of the related lease. Maintenance and repairs are charged against expense as incurred.
Impairment of Long-Lived Assets	'
	Impairment of Long-Lived Assets
	The Company evaluates long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If the estimated future cash flows (undiscounted and without interest charges) from the use of an asset are less than the carrying value, a write-down would be recorded to reduce the related asset to its estimated fair value. To date, no such write-downs have occurred.
Deferred Public Offering Costs	'
	Deferred Public Offering Costs
	Deferred public offering costs totaling $0.3 million at December 31, 2012 are included in prepaid and other current assets. These costs represent legal and accounting costs related to the Company’s efforts to raise capital through an IPO. At the completion of the IPO in April 2013, these costs were reclassified to additional paid-in capital as a reduction of the IPO proceeds.
Deferred Rent	'
	Deferred Rent
	The Company recognizes rent expense on a straight-line basis over the non-cancelable term of its operating lease and records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. The Company also records landlord-funded lease incentives, such as reimbursable leasehold improvements, as a deferred rent liability, which is amortized as a reduction of rent expense over the non-cancelable term of its operating lease.
Redeemable Convertible Preferred Stock Warrant Liability	'
	Redeemable Convertible Preferred Stock Warrant Liability
	Freestanding warrants for shares that are either putable or redeemable are classified as liabilities on the balance sheet at fair value. As further discussed in Note 6, the preferred stock underlying certain warrants was redeemable in certain circumstances, and as such the freestanding warrants that are related to the purchase of the Company’s Series F preferred stock were liabilities that should be recorded at the estimated fair value. At the end of each reporting period, changes in the estimated fair value during the period are recorded in other income.
Redeemable Convertible Preferred Stock	'
	Redeemable Convertible Preferred Stock
	The Company classified its redeemable convertible preferred stock, for which the Company did not control the redemption, outside of permanent equity. The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any offering costs, and the carrying value was adjusted to the redemption value at the end of each reporting period. These adjustments were effected through charges against additional paid-in capital and accumulated deficit.
Revenue Recognition	'
	Revenue Recognition
	The Company’s revenues generally consist of (i) contract and grant revenues – revenues generated under federal contracts and other awarded grants, and (ii) collaboration and licensing revenues – revenues related to non-refundable upfront fees, royalties and milestone payments earned under license agreements. Revenues are recognized when the following criteria are met: (1) persuasive evidence that an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured.
	For arrangements that involve the delivery of more than one element, each product, service and/or right to use assets is evaluated to determine whether it qualifies as a separate unit of accounting. This determination is based on whether the deliverable has “stand-alone value” to the customer. The consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the relative selling prices of each deliverable. The consideration allocated to each unit of accounting is recognized as the related goods and services are delivered, limited to the consideration that is not contingent upon future deliverables. If the arrangement constitutes a single unit of accounting, the revenue recognition policy must be determined for the entire arrangement and the consideration received is recognized over the period of inception through the date the last deliverable within the single unit of accounting is expected to be delivered. Revisions to the estimated period of recognition are reflected in revenue prospectively.
	Non-refundable upfront fees are recorded as deferred revenue and recognized into revenue as license fees from collaborations on a straight-line basis over the estimated period of the Company’s substantive performance obligations. If the Company does not have substantive performance obligations, the Company recognizes non-refundable upfront fees into revenue through the date the deliverable is satisfied. Analyzing the arrangement to identify deliverables requires the use of judgment and each deliverable may be an obligation to deliver services, a right or license to use an asset, or another performance obligation.
	Milestone payments are recognized when earned, provided that (i) the milestone event is substantive; (ii) there is no ongoing performance obligation related to the achievement of the milestone earned; and (iii) it would result in additional payments. Milestone payments are considered substantive if all of the following conditions are met: the milestone payment is non-refundable; achievement of the milestone was not reasonably assured at the inception of the arrangement; substantive effort is involved to achieve the milestone; and the amount of the milestone appears reasonable in relation to the effort expended, the other milestones in the arrangement; and the related risk associated with the achievement of the milestone. Contingent based event payments the Company may receive under a license or collaboration agreement will be recognized when received.
	For the years ended December 31, 2013, 2012 and 2011, contract and grant revenue consisted only of revenue from the BARDA contract as there was no grant revenue. The Company recognizes contract and grant revenue as qualifying research activities are conducted based on invoices received from the Company’s vendors. Changes in fringe and indirect rates are recognized as a change in estimate in the period such rate changes are approved by BARDA.
Clinical Trial Accruals	'
	Clinical Trial Accruals
	As part of the process of preparing financial statements, the Company is required to estimate its expenses resulting from its obligation under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate clinical trial expenses in its financial statements by matching those expenses with the period in which services and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with applicable personnel and outside service providers as to the progress or state of communication of trials, or the services completed. During the course of a clinical trial, the Company adjusts its rate of clinical trial expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low for any particular period. Through December 31, 2013, there had been no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. The Company’s clinical trial accrual is dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors.
Research and Development	'
	Research and Development
	Major components of research and development costs include cash compensation, stock based compensation, pre-clinical studies, clinical trial and related clinical manufacturing, drug development, materials and supplies, legal, regulatory compliance, and fees paid to consultants and other entities that conduct certain research and development activities on the Company’s behalf. Research and development costs, including upfront fees and milestones paid to contract research organizations, are expensed as goods as received or services rendered. Costs incurred in connection with clinical trial activities for which the underlying nature of the activities themselves do not directly relate to active research and development, such as costs incurred for market research and focus groups linked to clinical strategy as well as costs to build the Company’s brand, are not included in research and development costs but are reflected as general and administrative costs.
Interest Expense, Net	'
	Interest Expense, Net
	Interest expense, net includes interest earned on short-term investments, interest incurred on loans payable, the amortization of deferred financing costs related to fees paid to attorneys and other non-lender entities in order to acquire debt, and the amortization of debt discount related to fees paid to the lender in order to acquire debt.
Income Taxes	'
	Income Taxes
	Deferred tax assets and liabilities are determined based on differences between the financial and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are established when the Company determines that it is more likely than not that some portion of a deferred tax asset will not be realized. The Company has incurred operating losses from April 7, 2000 (inception) through December 31, 2013, and therefore has not recorded any current provision for income taxes.
	Additionally, the Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities based on the technical merits of the position. The tax benefit recognized in the financial statements for a particular tax position is based on the largest benefit that is more likely than not to be realized upon settlement. Accordingly, the Company establishes reserves for uncertain tax positions.
Share-Based Compensation	'
	Share-Based Compensation
	The Company measures and recognizes compensation expense for all share-based payment awards made to employees and directors, including employee stock options, based on estimated fair values. The fair value of share-based awards is estimated on the grant date using the Black-Scholes valuation model. The value of the portion of the award that is ultimately expected to vest is recorded as expense over the requisite service periods.
	The Company also accounts for equity instruments issued to non-employees using a fair value approach. The Company values equity instruments, stock options and warrants granted to lenders and consultants using the Black-Scholes valuation model. The measurement of non-employee share-based compensation is subject to periodic adjustments as the underlying equity instruments vest and is recognized as an expense over the term of the related financing or the period over which services are received.
Basic and Dilutive Net Loss Per Share of Common Stock	'
	Basic and Dilutive Net Loss Per Share of Common Stock
	Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, excluding the dilutive effects of converting redeemable convertible preferred stock, warrants to purchase redeemable convertible preferred stock and common stock, restricted stock and options. 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 redeemable convertible preferred stock and warrants to purchase redeemable convertible preferred stock, and options outstanding during the period calculated in accordance with the treasury stock method, but are excluded if their effect is anti-dilutive. Because the impact of these items is anti-dilutive during the periods of net loss, there was no difference between basic and diluted loss per share of common stock at December 31, 2013, 2012 and 2011.
	The calculation of weighted-average diluted shares outstanding excludes the dilutive effect of converting redeemable convertible preferred stock, warrants to purchase convertible preferred stock and options to purchase common stock, as the impact of such items are anti-dilutive during periods of net loss. Shares excluded from the calculations were 4,773,213,  11,259,579 and 11,034,134 for the years ended December 31, 2013, 2012 and 2011, respectively.
Segments	'
	Segments
	The Company operates in only one segment. The chief operating decision-maker, who is the Company’s Chief Executive Officer, and management use cash flows as the primary measure to manage the business and do not segment the business for internal reporting or decision making.

The_Business_and_Summary_of_Si2

The Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
The Business and Summary of Significant Accounting Policies [Abstract]	'
Assets and Liabilities Measured at Fair Value on a Recurring Basis	'
	Below is a table that presents information about certain assets and liabilities measured at fair value on a recurring basis:
					Fair Value Measurements at
					31-Dec-13
		December 31,			Quoted Prices in		Significant Other		Significant
		2013			Active Markets		Observable Inputs		Unobservable Inputs
					for Identical Assets		(Level 2)		(Level 3)
					(Level 1)
		(in thousands)
	Cash equivalents	$	107,349		$	107,349	$	—	$	—
					Fair Value Measurements at
					31-Dec-12
		December 31,			Quoted Prices in		Significant Other		Significant
		2012			Active Markets		Observable Inputs		Unobservable Inputs
					for Identical Assets		(Level 2)		(Level 3)
					(Level 1)
		(in thousands)
	Cash equivalents	$	17,687		$	16,381	$	1,306	$	—
	Short-term investments		9,849			—		9,849		—
	Redeemable convertible preferred stock warrant liability		7,512			—		—		7,512
Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis	'
	Below is a table that presents a reconciliation of the beginning and ending balances of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3):
		Fair Value
		Measurements
		(Level 3)
		(in thousands)
	Redeemable Convertible Preferred Stock Warrant Liability
	Balance at January 1, 2012	$	6,491
	Issuance		174
	Fair value increase recorded in other expense		847
	Fair value at December 31, 2012		7,512
	Fair value increase recorded in other expense		6,590
	Reclassification of warrant liability to additional paid-in capital		(14,102	)
	Fair value at December 31, 2013	$	—
Schedule of Prepaid and Other Current Assets	'
	Prepaid and other current assets consist of the following:
		31-Dec-13			31-Dec-12
		(in thousands)
	Prepaid development expenses	$	2,433		$	486
	Deferred public offering costs		—			273
	Other prepaid and other current assets		332			224
		$	2,765		$	983
Schedule of Accrued Liabilities	'
	Accrued liabilities consist of the following:
		31-Dec-13			31-Dec-12
		(in thousands)
	Accrued compensation	$	1,779		$	560
	Accrued development expenses		350			98
	Other accrued liabilities		291			248
		$	2,420		$	906

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Investments [Abstract]	'
Summary of Available-for-Sale Securities	'
	The following table summarizes available-for-sale securities as of December 31, 2012:
		Amortized Cost		Gross Unrealized		Gross Unrealized			Estimated
				Gains		Losses			Fair Value
		(in thousands)
	Corporate bonds	$	8,353	$	—	$	(2	)	$	8,351
	Commercial paper		1,498		—		—			1,498
	Total	$	9,851	$	—	$	(2	)	$	9,849

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2013
Property and Equipment [Abstract]	'
Property and Equipment	'
	Property and equipment consist of the following:
		31-Dec-13			31-Dec-12
		(in thousands)
	Lab equipment	$	873		$	958
	Leasehold improvements		78			78
	Computer equipment		324			393
	Office furniture and equipment		222			212
			1,497			1,641
	Less accumulated depreciation		(1,159	)		(1,234	)
		$	338		$	407

Loan_Payable_Tables

Loan Payable (Tables)	12 Months Ended
	Dec. 31, 2013
Loan Payable [Abstract]	'
Schedule of Future Payments under LSA	'
	The future payments under the LSA are as follows (in thousands):
	Years ending December 31,
	2014	$	6,322
	2015		4,508
			10,830
	Less: amount representing interest		(780	)
	Total payments under LSA	$	10,050

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies [Abstract]	'
Schedule of Future Minimum Rental Payments for Operating Leases	'
	The Company has the following minimum payments under noncancelable operating lease obligations that existed at December 31, 2013 (in thousands):
	Years ending December 31,
	2014	$	331
	2015		275
	2016		245
	2017		243
	2018		41
		$	1,135

Redeemable_Convertible_Preferr1

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2013
Summary of Authorized, Issued and Outstanding Shares of Redeemable Convertible Preferred Stock	'
	The following table summarizes the authorized, issued and outstanding shares of redeemable convertible preferred stock as of December 31, 2012:
		Authorized				Issued and
		Shares				Outstanding Shares
	Series A		800,000				800,000
	Series B		2,233,879				2,233,879
	Series B-1		2,054,333				2,033,333
	Series C		5,141,690				5,141,690
	Series D		11,354,526				11,295,846
	Series E		7,894,871				7,894,871
	Series F		40,200,000				22,004,895
	Total Shares		69,679,299				51,404,514
Common Stock [Member]	'
Schedule of Warrants Issued, Outstanding and Exercisable	'
	The following warrants for the purchase of common stock were issued, outstanding and exercisable at December 31, 2013:
	Class	Date		Shares				Price Per Share		Expiration
	Common	7-Feb-11			1,337,845			$	7.26	Feb-18
Redeemable Convertible Preferred Stock [Member]	'
Schedule of Warrants Issued, Outstanding and Exercisable	'
	The following warrants for the purchase of preferred stock were issued, outstanding and exercisable at December 31, 2012:
	Class	Date		Shares				Price Per Share		Expiration
	Series B-1	5-Nov-03			21,000			$	1.500	Nov-13
	Series D	24-Nov-08			58,680			$	2.045	Nov-18
	Series F	7-Feb-11			5,501,215			$	2.045	Feb-18
	Series F	27-Jan-12			146,700			$	2.045	Jan-22

Stockholders_Equity_Deficit_Ta

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2013
Schedule of Shares Reserved for Future Issuance	'
	The following shares of common stock reserved for future issuances:
		31-Dec-13				31-Dec-12
	Conversion of preferred stock and preferred stock warrants		—				16,093,483
	Exercise of common stock warrants		1,337,845				—
	Stock options issued and outstanding		1,946,823				2,593,423
	Restricted Stock units outstanding		-				43,199
	Authorized for future purchases under the 2013 Employee Stock Purchase Plan		704,225				—
	Authorized for future grants under the 2013 Equity Incentive Plan		1,681,932				—
	Authorized for future grants under the 2012 Equity Incentive Plan		—				427,933
			5,670,825				19,158,038
Summary of Activity Related to Stock Options	'
	A summary of activity related to the Company’s stock options is as follows:
		Number of Options				Weighted-Average				Weighted-Average
		Outstanding				Exercise Price				Remaining Contractual
										Life (in Years)
	Balance, January 1, 2012		2,631,415			$	2.24				7.69
	Granted		382,167				3.24				—
	Exercised		(16,530	)			0.82				—
	Expired or Canceled		(102,228	)			2.63				—
	Forfeited		(301,401	)			1.69				—
	Balance, December 31, 2012		2,593,423			$	2.45				7.36
	Granted		292,906				10.62				—
	Exercised		(801,049	)			2.43				—
	Expired or Canceled		(2,816	)			1.57				—
	Forfeited		(135,641	)			4.55				—
	Balance, December 31, 2013		1,946,823			$	3.54				7.03
	Exercisable at December 31, 2013		1,266,070			$	2.32				6.21
	Vested or expected to vest at December 31, 2013		1,952,222			$	3.5				7.02
Fair Value of Option Vested and Share-Based Compensation Expense	'
	The fair value of options vested and share-based compensation expense recognized are as follows:
		Year Ended December 31,
		2013				2012				2011
		(in thousands)
	Research and development:
	Employee	$	537			$	336			$	315
	Non-employee		67				80				—
	General and administrative:
	Employee		458				921				651
	Non-employee		82				59				—
		$	1,144			$	1,396			$	966
Summary of Activity Related to Restricted Stock Units	'
	A summary of activity related to the Company’s RSUs is as follows:
		Number of Restricted
		Stock Units Outstanding
	Balance, December 31, 2012		43,199
	Granted		59,348
	Share issuance		(102,547	)
	Balance, December 31, 2013		—
Employee [Member]	'
Schedule of Fair Value Assumptions	'
		Employees
		Year Ended December 31,
		2013				2012				2011
	Dividend yield		0.00	%			0.00	%			0.00	%
	Weighted-average risk-free interest rate		1.49	%			0.86	%			2.85	%
	Volatility		76.40	%			80.55	%			82.00	%
	Expected term (in years)		6.1				6.0				7.0
	Weighted-average fair value per option	$	2.52			$	1.93			$	1.74
Non-Employee [Member]	'
Schedule of Fair Value Assumptions	'
				Non-Employees
				Year Ended December 31,
		2013						2012				2011
	Dividend yield				0.00	%			0.00	%			0.00	%
	Weighted-average risk-free interest rate				1.30	%			0.78	%			0.40	%
	Volatility				79.69	%			81.77	%			77.80	%
	Expected term (in years)				6.2				5.8				2.7
	Weighted-average fair value per option		$		5.01			$	3.48			$	3.38

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Taxes [Abstract]	'
Components of Deferred Tax Assets and Liabilities	'
	The components of deferred tax assets and liabilities at December 31, 2013 and 2012 are as follows:
		December 31,
		2013					2012
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$		40,721			$	31,431
	Research and development expenses			127				34
	Capitalized Section 174 expenses			69				80
	Research and development credits			2,640				941
	Accrued bonuses			405				54
	Other			497				445
	Total gross deferred tax assets			44,459				32,985
	Valuation allowance			(44,405	)			(32,841			)
				54				144
	Deferred tax liabilities:
	Other			(54	)			(144			)
	Total deferred tax liabilities			(54	)			(144			)
	Net deferred tax assets	$		—			$	—
Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate	'
	A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2013, 2012, and 2011:
		2013							2012						2011
		Amount			% of Pretax Earnings				Amount			% of Pretax Earnings			Amount			% of Pretax Earnings
		(in thousands)
	Income tax benefit at statutory rate	$	(12,392	)		34	%		$	(1,499	)		34	%	$	(8,700	)		34	%
	State income taxes		(852	)		2.3	%			(100	)		2.3	%		(1,164	)		4.6	%
	Research and development credits		(2,265	)		6.2	%			—			0	%		(1,171	)		4.6	%
	Permanent items		3,060			(8.4	)%			868			(19.7	)%		964			(3.8	)%
	Provision to return adjustments		320			(0.9	)%			2			0	%		12			0	%
	Effect of change in state tax rate		-1			0	%			609			(13.9	)%		630			(2.5	)%
	Increase in unrecognized tax benefits		566			(1.5	)%			—			0	%		314			(1.2	)%
	Valuation allowance		11,564			(31.7	)%			120			(2.7	)%		9,115			(35.7	)%
	Net benefit	$	—			0	%		$	—			0	%	$	—			0	%
Summary of Uncertain Tax Benefit	'
	Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the year ended December 31, 2013, as follows (in thousands):
	Balance at December 31, 2011	$	314
	Increases related to 2012		—
	Balance at December 31, 2012		314
	Increase related to 2013		297
	Increase related to prior periods		269
	Balance at December 31, 2013	$	880

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
Schedule of Quarterly Financial Information	'
	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2013 and 2012 are as follows (in thousands, except per share data):
		2013 Quarter
		Fourth		Third		Second		First
	Total revenues	$	879	$	912	$	808	$	1,771
	Operating loss		-7,979		-6,436		-7,656		-6,548
	Net loss		-8,174		-6,706		-12,459		-9,107
	Net loss per common share, basic and diluted	$	-0.31	$	-0.26	$	-0.91	$	-22.58
	Weighted average shares outstanding, basic and diluted		26,416,787		25,866,109		23,067,201		1,534,016
		2012 Quarter
		Fourth		Third		Second		First
	Total revenues	$	3,581	$	20,856	$	6,205	$	3,078
	Operating (loss) income		-4,143		11,272		-4,422		-5,490
	Net (loss) income		-4,326		11,142		-4,324		-6,898
	Net (loss) income per common share, basic	$	-3.9	$	6.70	$	-3.44	$	-5.14
	Net (loss) income per common share, diluted	$	-3.9	$	0.11	$	-3.44	$	-5.14
	Weighted average shares outstanding, basic		1,532,633		1,529,442		1,518,753		1,517,465
	Weighted average shares outstanding, diluted		1,532,633		52,933,956		1,518,753		1,517,465

The_Business_and_Summary_of_Si3

The Business and Summary of Significant Accounting Policies (Narrative) (Details) (USD $)

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

12 Months Ended

Mar. 25, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Apr. 10, 2013

Apr. 16, 2013

Apr. 10, 2010

Oct. 23, 2013

Apr. 10, 2013

Apr. 10, 2013

Apr. 10, 2013

Dec. 31, 2012

Apr. 10, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

item

segment

Over Allotment Options [Member]

IPO [Member]

Secondary Offering [Member]

Series F [Member]

Series F [Member]

Warrant [Member]

Warrant [Member]

Warrant [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

IPO [Member]

IPO [Member]

Series F [Member]

Warrant [Member]

Series F [Member]

Warrant [Member]

Description of Business

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Stock split, reverse description

'the Company's board of directors approved and implemented a 3.55-for-1 reverse stock split of the Company's outstanding common stock

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Reverse stock split, conversion ratio

3.55

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Stock issued during the period, shares

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1,098,000

7,320,000

2,476,995

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Issuance of common stock, per share price

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$14

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$14

$14

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Issuance of common stock, value

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$14,300,000

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Proceeds from initial public offering

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107,634,000

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93,300,000

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Public offering underwriting discounts and commissions

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1,100,000

7,100,000

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Offering expenses

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10,217,696

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2,100,000

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Conversion of stock, shares converted

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15,556,091

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'

'

Warrants to purchase common stock

'

'

'

'

41,323

'

'

'

'

'

'

'

1,613,395

'

'

'

'

'

'

Investments Related to Corporate Bonds and Commercial Paper

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available for sale securities losses, other-than-temporary

'

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value of Financial Instruments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Volatility

'

79.69%

81.77%

77.80%

'

'

'

'

'

'

79.00%

79.00%

'

'

'

'

'

'

'

Fair value

'

'

'

'

'

'

'

'

$3.94

'

'

'

'

'

$2.85

'

'

$2.19

'

Expected term

'

'6 years 2 months 12 days

'5 years 9 months 18 days

'2 years 8 months 12 days

'

'

'

'

'

'

'2 years 6 months

'

'

'

'

'5 years

'

'

'8 months

Risk free interest rate

'

1.30%

0.78%

0.40%

'

'

'

'

'

'

0.24%

'

'

'

'

'

'

'

'

Dividend yield

'

0.00%

0.00%

0.00%

'

'

'

'

'

'

0.00%

'

'

'

'

'

'

'

'

Expected liquidity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

31.00%

'

'

2.00%

Property and Equipment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Property and equipment, useful life

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 years

'

'

'3 years

'

'

Property and equipment, useful life, leasehold improvements

'

'amortized over the shorter of the useful life of the asset or the term of the related lease

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Impairment of long-lived assets

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred Public Offering Costs

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred public offering costs

'

'

$273,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Per share information:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Anti-dilutive securities excluded from the calculation loss per share

'

4,773,213

11,259,579

11,034,134

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Segments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of operating segments

'

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

The_Business_and_Summary_of_Si4

The Business and Summary of Significant Accounting Policies (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Liabilities, fair value	'	$7,512	$6,491
Cash Equivalents [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Assets, fair value	107,349	17,687	'
Cash Equivalents [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Assets, fair value	107,349	16,381	'
Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Assets, fair value	'	1,306	'
Short-term Investments [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Assets, fair value	'	9,849	'
Short-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Assets, fair value	'	9,849	'
Redeemable Convertible Preferred Stock [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Liabilities, fair value	'	7,512	'
Redeemable Convertible Preferred Stock [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'	'
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]	'	'	'
Liabilities, fair value	'	$7,512	'

The_Business_and_Summary_of_Si5

The Business and Summary of Significant Accounting Policies (Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis) (Details) (Significant Unobservable Inputs (Level 3) [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Significant Unobservable Inputs (Level 3) [Member]	'	'
Beginning of period	$7,512	$6,491
Issuance	'	174
Fair value increase recorded in other expense	6,590	847
Reclassification of warrant liability to additional paid-in capital	-14,102	'
Ending period	'	$7,512

The_Business_and_Summary_of_Si6

The Business and Summary of Significant Accounting Policies (Schedule of Prepaid and Other Current Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
The Business and Summary of Significant Accounting Policies [Abstract]	'	'
Prepaid development expenses	$2,433	$486
Deferred public offering costs	'	273
Other prepaid and other current assets	332	224
Prepaid and other current assets, total	$2,765	$983

The_Business_and_Summary_of_Si7

The Business and Summary of Significant Accounting Policies (Schedule of Accrued Liabilities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
The Business and Summary of Significant Accounting Policies [Abstract]	'	'
Accrued compensation	$1,779	$560
Accrued development expenses	350	98
Other accrued liabilities	291	248
Accrued liabilities, current, total	$2,420	$906

Investments_Details

Investments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]	'	'
Amortized cost	'	$9,851,000
Gross unrealized losses	'	-2,000
Estimated fair value	'	9,849,000
Investments maturity period, maximum	'	'1 year
Short-term investments	0	'
Long-term investments	0	'
Corporate Bonds [Member]	'	'
Schedule of Investments [Line Items]	'	'
Amortized cost	'	8,353,000
Gross unrealized losses	'	-2,000
Estimated fair value	'	8,351,000
Commercial Paper [Member]	'	'
Schedule of Investments [Line Items]	'	'
Amortized cost	'	1,498,000
Estimated fair value	'	$1,498,000

Property_and_Equipment_Details

Property and Equipment (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$1,497	$1,641
Less accumulated depreciation	-1,159	-1,234
Property and equipment, net	338	407
Lab Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	873	958
Leasehold Improvements [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	78	78
Computer Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	324	393
Office Furniture and Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$222	$212

Loan_Payable_Narrative_Details

Loan Payable (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Apr. 10, 2013

Jan. 27, 2012

Dec. 31, 2013

Jan. 27, 2012

Dec. 31, 2013

Jan. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Feb. 07, 2011

Dec. 31, 2013

Dec. 31, 2013

Second Tranche [Member]

Second Tranche [Member]

First Tranche [Member]

First Tranche [Member]

Loan And Security Agreement [Member]

Loan And Security Agreement [Member]

Series F [Member]

Series F [Member]

Series F [Member]

Second Tranche [Member]

First Tranche [Member]

Line of Credit Facility [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loan and security agreement, maximum capacity

'

'

'

'

$15,000,000

'

'

'

'

'

'

'

'

'

Loan and security agreement, outstanding

'

'

'

'

'

'

'

'

3,000,000

'

'

'

'

'

Loan and security agreement, remaining capacity

'

'

'

'

'

'

12,000,000

'

'

'

'

'

'

'

Loan payment

'

'

'

'

'

'

'

2,600,000

'

'

'

'

'

'

Deferred financing costs

'

'

'

'

'

'

'

100,000

'

'

'

'

'

'

Interest only period

'

'

'

'

'

'6 months

'

'12 months

'

'

'

'

'

'

Principal and interest amortization period

'

'

'

'

'

'32 months

'

'30 months

'

'

'

'

'

'

Loan and security agreement, interest rate

'

'

'

'

'

'

'

8.25%

'

'

'

'

'

'

Interest expense

$1,232,000

$776,000

$212,000

'

'

'

'

'

'

$100,000

$100,000

'

'

'

Warrant strike price

2.045

'

'

7.26

'

'

'

'

'

'

'

2.045

'

'

Aggregate amount of advances, percentage

2.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

Warrants to purchase common stock

'

'

'

41,323

'

'

'

'

'

'

'

'

117,360

29,340

Loan_Payable_Schedule_of_Futur

Loan Payable (Schedule of Future Payments under LSA) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Repayments of debt	$10,050
Principal and Interest Portion [Member]	'
Repayments of debt	10,830
Interest Portion [Member]	'
Repayments of debt	-780
2014 [Member]	'
Repayments of debt	6,322
2015 [Member]	'
Repayments of debt	$4,508

Commitments_and_Contingencies_1

Commitments and Contingencies (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies [Abstract]	'	'
Operating leases, rent expense	$0.50	$0.40

Commitments_and_Contingencies_2

Commitments and Contingencies (Schedule of Future Minimum Rental Payments for Operating Leases) (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Commitments and Contingencies [Abstract]	'
2014	$331
2015	275
2016	245
2017	243
2018	41
Operating leases, future minimum payments due, total	$1,135

Redeemable_Convertible_Preferr2

Redeemable Convertible Preferred Stock (Narrative) (Details) (USD $)

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

Apr. 10, 2013

Feb. 07, 2011

Dec. 31, 2013

Feb. 07, 2011

Dec. 31, 2012

Dec. 31, 2013

Jan. 27, 2012

Apr. 10, 2013

Dec. 31, 2013

Dec. 31, 2012

Jan. 27, 2012

Apr. 16, 2013

Apr. 10, 2013

Nov. 05, 2013

24-May-13

Dec. 31, 2013

Series F [Member]

Series F [Member]

Series F [Member]

Series F [Member]

Series F [Member]

Warrant [Member]

Warrant [Member]

Warrant [Member]

Warrant [Member]

Warrant [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Silicon Valley Bank [Member]

IPO Completion [Member]

Silicon Valley Bank [Member]

IPO [Member]

IPO Completion [Member]

Redeemable convertible preferred stock issued

'

'

51,404,514

22,004,895

'

22,004,895

'

'

'

'

'

'

'

'

'

'

Redeemable convertible preferred stock issued, par value per share

'

'

'

$0.00

'

'

'

'

'

'

'

'

'

'

'

'

Redeemable convertible preferred stock issued, redemption price per share

'

'

'

$2.04

$2.04

'

$2.04

'

'

'

'

'

'

'

'

'

Redeemable convertible preferred stock, warrants issued

'

5,501,215

'

'

'

'

146,700

1,549,628

'

'

41,323

'

1,613,395

'

'

'

Redeemable convertible preferred stock, warrants issued, issuance costs

'

'

'

$200,000

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from issuance of redeemable preferred stock

'

'

'

45,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Warrants expiration date

'

'

'

'

1-Feb-18

'

'

4-Feb-18

'

'

'

'

'

'

'

1-Feb-18

Percentage of the aggregate amount of advances made

'

'

'

'

'

'

2.00%

'

'

'

'

'

'

'

'

'

Aggregate number of common shares converted from redeemable convertible preferred stock

15,556,091

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other expense as a result of fair valuation of warrants

'

'

'

'

'

'

'

'

6,400,000

800,000

'

'

'

'

'

'

Class of warrant or rights exercised

'

'

'

'

'

'

'

'

'

'

'

211,783

'

3,906

37,600

'

Proceeds from exercise of warrants

'

'

$1,537,000

'

'

'

'

'

'

'

'

$1,500,000

'

'

'

'

Warrants exercise price

7.26

'

2.045

2.045

'

'

'

7.26

'

'

7.26

'

'

'

'

7.26

Redeemable_Convertible_Preferr3

Redeemable Convertible Preferred Stock (Summary of Authorized, Issued and Outstanding Shares of Redeemable Convertible Preferred Stock) (Details)	Dec. 31, 2013	Feb. 07, 2011
Authorized shares	69,679,299	'
Issued and outstanding shares	51,404,514	'
Series A [Member]	'	'
Authorized shares	800,000	'
Issued and outstanding shares	800,000	'
Series B [Member]	'	'
Authorized shares	2,233,879	'
Issued and outstanding shares	2,233,879	'
Series B-1 [Member]	'	'
Authorized shares	2,054,333	'
Issued and outstanding shares	2,033,333	'
Series C [Member]	'	'
Authorized shares	5,141,690	'
Issued and outstanding shares	5,141,690	'
Series D [Member]	'	'
Authorized shares	11,354,526	'
Issued and outstanding shares	11,295,846	'
Series E [Member]	'	'
Authorized shares	7,894,871	'
Issued and outstanding shares	7,894,871	'
Series F [Member]	'	'
Authorized shares	40,200,000	'
Issued and outstanding shares	22,004,895	22,004,895

Redeemable_Convertible_Preferr4

Redeemable Convertible Preferred Stock (Schedule of Warrants Issued, Outstanding and Exercisable) (Details) (USD $)	Dec. 31, 2013	Apr. 10, 2013	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Feb. 07, 2011	Dec. 31, 2012	Dec. 31, 2013
			Series B-1 [Member]	Series D [Member]	Series F [Member]	Series F [Member]	Series F 2nd Occurrence [Member]	Common Stock [Member]
Warrants date exercisable	'	'	5-Nov-03	24-Nov-08	7-Feb-11	'	27-Jan-12	7-Feb-11
Warrants issued, outstanding and exercisable	'	'	21,000	58,680	5,501,215	'	146,700	1,337,845
Redeemable convertible preferred stock issued, redemption price per share	'	'	$1.50	$2.04	$2.04	$2.04	$2.04	'
Warrants exercise price	2.045	7.26	'	'	'	2.045	'	7.26
Warrants expiration date	'	'	1-Nov-13	1-Nov-18	1-Feb-18	'	1-Jan-22	1-Feb-18

Stockholders_Equity_Deficit_Na

Stockholders' Equity (Deficit) (Narrative) (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Apr. 30, 2013

Apr. 10, 2013

Dec. 31, 2012

Dec. 31, 2013

Apr. 10, 2013

Feb. 28, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Restricted Stock Units (RSUs) [Member]

The 2012 Plan [Member]

The 2012 Plan [Member]

The 2013 Plan [Member]

The 2013 Plan [Member]

The 2013 ESPP [Member]

The 2013 ESPP [Member]

Modified Grants [Member]

Modified Grants [Member]

Maximum [Member]

Three Individuals [Member]

One Individual [Member]

The 2013 Plan [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, shares authorized

200,000,000

89,700,000

'

'

'

'

'

'

'

'

'

'

'

Common stock, shares issued

26,664,972

1,533,996

'

'

'

'

'

'

'

'

'

'

'

Common stock, shares outstanding

26,664,972

1,533,996

'

'

'

'

'

'

'

'

'

'

'

Number of shares outstanding under the plan

1,946,823

2,593,423

2,631,415

'

'

'

'

'

'

'

'

'

'

Number of shares authorized to be granted

'

'

'

'

244,717

427,933

1,681,932

1,408,450

704,225

704,225

'

'

2,816,901

Number of shares authorized, increase amount

'

'

'

'

'

'

'

'

422,535

'

'

'

'

Percentage of total number of shares of capital stock outstanding

'

'

'

'

'

'

2.50%

'

1.00%

'

'

'

'

Aggregate intrinsic value of options outstanding

$16,200,000

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options exercisable

16,200,000

'

'

'

'

'

'

'

'

'

'

'

'

Intrinsic value of options exercised

12,400,000

18,000

16,000

'

'

'

'

'

'

'

'

'

'

Increase in compensation expense

'

'

'

'

'

'

'

'

'

'

30,000

300,000

'

Exercise of stock options

1,946,000

14,000

30,000

'

'

'

'

'

'

'

'

'

'

Tax benefit from stock options exercised

0

0

'

'

'

'

'

'

'

'

'

'

'

Unrecognized compensation costs

'

'

'

'

'

'

2,500,000

'

'

'

'

'

'

Unrecognized compensation costs, period of recognition

'

'

'

'

'

'

'2 years 6 months 15 days

'

'

'

'

'

'

Compensation expense, allocated

'

'

'

$1,900,000

'

'

'

'

'

'

'

'

'

Stockholders_Equity_Deficit_Sc

Stockholders' Equity (Deficit) (Schedule of Shares Reserved for Future Issuance) (Details)	Dec. 31, 2013	Dec. 31, 2012	Apr. 10, 2013	Dec. 31, 2012	Dec. 31, 2013	Apr. 10, 2013	Dec. 31, 2013	Feb. 28, 2013
			The 2012 Plan [Member]	The 2012 Plan [Member]	The 2013 Plan [Member]	The 2013 Plan [Member]	The 2013 ESPP [Member]	The 2013 ESPP [Member]
Conversion of preferred stock and preferred stock warrants	'	16,093,483	'	'	'	'	'	'
Exercise of common stock warrants	1,337,845	'	'	'	'	'	'	'
Stock options issued and outstanding	1,946,823	2,593,423	'	'	'	'	'	'
Restricted Stock units outstanding	'	43,199	'	'	'	'	'	'
Authorized for future grants under the plan	'	'	244,717	427,933	1,681,932	1,408,450	704,225	704,225
Shares of common stock reserved for future issuance	5,670,825	19,158,038	'	'	'	'	'	'

Stockholders_Equity_Deficit_As

Stockholders' Equity (Deficit) (Assumption Used to Determine the Fair Value of Options Granted) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]	'	'	'
Dividend yield	0.00%	0.00%	0.00%
Expected term	'6 years 2 months 12 days	'5 years 9 months 18 days	'2 years 8 months 12 days
Volatility	79.69%	81.77%	77.80%
Weighted-average risk-free interest rate	1.30%	0.78%	0.40%
Weighted-average fair value per option	$5.01	$3.48	$3.38
Employee Stock Option [Member]	'	'	'
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]	'	'	'
Dividend yield	0.00%	0.00%	0.00%
Expected term	'6 years 1 month 6 days	'6 years	'7 years
Volatility	76.40%	80.55%	82.00%
Weighted-average risk-free interest rate	1.49%	0.86%	2.85%
Weighted-average fair value per option	$2.52	$1.93	$1.74

Stockholders_Equity_Deficit_Su

Stockholders' Equity (Deficit) (Summary of Activity Related to Stock Options) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stockholders' Equity (Deficit) [Abstract]	'	'	'
Number of options outstanding, Beginning balance	2,593,423	2,631,415	'
Number of options outstanding, Granted	292,906	382,167	'
Number of options outstanding, Exercised	-801,049	-16,530	'
Number of options outstanding, Expired or Canceled	-2,816	-102,228	'
Number of options outstanding, Forfeited	-135,641	-301,401	'
Number of options outstanding, Ending balance	1,946,823	2,593,423	2,631,415
Number of options outstanding, Exercisable	1,266,070	'	'
Number of options outstanding, Vested and expected to vest	1,952,222	'	'
Weighted-average exercise price, beginning balance	$2.45	$2.24	'
Weighted-average exercise price, Granted	$10.62	$3.24	'
Weighted-average exercise price, Exercised	$2.43	$0.82	'
Weighted-average exercise price, Expired or Canceled	$1.57	$2.63	'
Weighted-average exercise price, Forfeited	$4.55	$1.69	'
Weighted-average exercise price, Ending balance	$3.54	$2.45	$2.24
Weighted-average exercise price, Exercisable	$2.32	'	'
Weighted-average exercise price, Vested or expected to vest	$3.50	'	'
Weighted-average remaining contractual life (in years), beginning	'7 years 11 days	'7 years 4 months 10 days	'7 years 8 months 9 days
Weighted-average remaining contractual life (in years), ending	'7 years 11 days	'7 years 4 months 10 days	'7 years 8 months 9 days
Weighted-average remaining contractual life (in years), Exercisable	'6 years 2 months 16 days	'	'
Weighted-average remaining contractual life (in years), Vested or expected to vest	'7 years 7 days	'	'

Stockholders_Equity_Deficit_Su1

Stockholders' Equity (Deficit) (Summary of Activity Related to Restricted Stock Units) (Details)	Dec. 31, 2012	Dec. 31, 2013
		Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]	'	'
Balance, December 31, 2012	43,199	43,199
Granted	'	59,348
Shares issuance	'	-102,547
Balance, September 30, 2013	43,199	'

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2007

Dec. 31, 2002

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Jan. 01, 2014

Domestic Tax Authority [Member]

Domestic Tax Authority [Member]

State and Local Jurisdiction [Member]

State and Local Jurisdiction [Member]

Minimum [Member]

Maximum [Member]

Subsequent Event [Member]

Loss limitation ownership change benchmark amount

$6,700,000

'

$762,000

$64,000

'

'

'

'

'

'

'

'

Operating loss carryforwards

'

'

'

'

'

117,500,000

83,600,000

106,000,000

65,800,000

'

'

'

Operating loss carryforwards, expiration dates

'

'

'

'

'

'2020

'

'2023

'

'

'

'

Excess tax benefits from exercise of stock options in net operating loss carryforwards

7,300,000

'

'

'

'

'

'

'

'

'

'

'

Tax credit carryforward, deferred tax asset

'

'

'

'

'

3,500,000

'

'

'

'

'

'

Tax credit carryforward, expiration date

'

'

'

'

'

31-Dec-22

'

'

'

'

'

'

Increase to valuation allowance, deferred tax assets

1,200,000

1,100,000

'

'

'

'

'

'

'

'

'

'

Income tax examination, year under examination

'

'

'

'

'

'

'

'

'

'2000

'2013

'

Income tax examination, penalties and interest accrued

'

'

'

'

'

'

'

'

'

'

'

0

Unrecognized tax benefits, gross

$880,000

$314,000

'

'

$314,000

'

'

'

'

'

'

'

Income_Taxes_Components_of_Def

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Deferred tax assets:	'	'
Net operating loss carryforwards	$40,721	$31,431
Research and development expenses	127	34
Capitalized Section 174 expenses	69	80
Research and development credits	2,640	941
Accrued bonuses	405	54
Other	497	445
Total gross deferred tax assets	44,459	32,985
Valuation allowance	-44,405	-32,841
Deferred tax assets, net of valuation allowance, total	54	144
Deferred Tax Liabilities, Gross [Abstract]	'	'
Other	-54	-144
Total deferred tax liabilities	-54	-144
Net deferred tax assets	'	'

Income_Taxes_Components_of_the

Income Taxes (Components of the Net Income Tax Benefit) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]	'	'	'
Valuation allowance	($11,564)	($120)	($9,115)

Income_Taxes_Reconciliation_of

Income Taxes (Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate) (Alternate) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]	'	'	'
Income tax benefit at statutory rate	($12,392)	($1,499)	($8,700)
Income tax benefit at statutory rate, tax rate	34.00%	34.00%	34.00%
State income taxes	-852	-100	-1,164
State income taxes, tax rate	2.30%	2.30%	4.60%
Research and development credits	-2,265	'	-1,171
Research and development credits, tax rate	6.20%	0.00%	4.60%
Permanent items	3,060	868	964
Permanent items, tax rate	-8.40%	-19.70%	-3.80%
Provision to return adjustments	320	2	12
Provision to return adjustments, tax rate	-0.90%	0.00%	0.00%
Effect of change in state tax rate	-1	609	630
Effect of change in state tax rate, tax rate	0.00%	-13.90%	-2.50%
Increase in unrecognized tax benefits	566	'	314
Increase in unrecognized tax benefits, tax rate	-1.50%	0.00%	-1.20%
Valuation allowance	$11,564	$120	$9,115
Valuation allowance, tax rate	-31.70%	-2.70%	-35.70%
Net income tax benefit, tax rate	0.00%	0.00%	0.00%

Income_Taxes_Summary_of_Uncert

Income Taxes (Summary of Uncertain Tax Benefit) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Abstract]	'	'
Beginning balance	$314	$314
Increase related to 2013	297	'
Increase related to prior periods	269	'
Ending balance	$880	$314

Significant_Agreements_Details

Significant Agreements (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Jul. 31, 2012

31-May-02

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

31-May-02

Jul. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

CMX001 [Member]

CMX157 [Member]

Merck, Sharp and Dohme Corp. [Member]

Regents Of University Of California [Member]

Regents Of University Of California [Member]

Regents Of University Of California [Member]

Research and Development Arrangement [Member]

Research and Development Arrangement [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

CMX157 [Member]

Merck, Sharp and Dohme Corp. [Member]

Research and Development Arrangement [Member]

Research and Development Arrangement [Member]

contract

Scenario, Plan [Member]

Long-term Purchase Commitment [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Milestone payments

'

'

'

'

'

'

'

'

'

'

'

$3,400,000

$151,000,000

'

'

Number of options outstanding, Granted

292,906

382,167

'

'

'

'

64,788

'

'

'

'

'

'

'

'

Sublicense fee percentage

'

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

Sublicense fee payable, maximum percentage

'

'

'

5.00%

10.00%

'

'

'

'

'

'

'

'

'

'

Royalties percentage

'

'

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

Contract revenue

4,370,000

16,275,000

12,046,000

'

'

'

'

'

'

5,300,000

'

'

'

'

5,300,000

Other expenses

'

'

'

'

'

'

'

0

900,000

'

'

'

'

'

'

Reimbursement revenue

'

'

'

'

'

'

'

'

'

'

'

'

'

'

75,800,000

Number of extension periods

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

Length of first option segment period

'

'

'

'

'

'

'

'12 months

'

'

'

'

'

'

'

Other segments, period

'

'

'

'

'

'

'

'

'

'

'1 year

'

'

'

'

Upfront payment, receivable

'

'

'

'

'

$17,500,000

'

'

'

'

'

'

'

'

'

Product royalty period

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statements Of Operations And Comprehensive Loss [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Total revenues	$879	$912	$808	$1,771	$3,581	$20,856	$6,205	$3,078	$4,370	$33,720	$12,101
Operating (loss) income	-7,979	-6,436	-7,656	-6,548	-4,143	11,272	-4,422	-5,490	-28,619	-2,783	-24,992
Net (loss) income	($8,174)	($6,706)	($12,459)	($9,107)	($4,326)	$11,142	($4,324)	($6,898)	($36,445)	($4,406)	($25,589)
Net loss per common share, basic and diluted	($0.31)	($0.26)	($0.91)	($22.58)	'	'	'	'	($3.65)	($5.75)	($23.49)
Weighted-average shares outstanding, basic and diluted	26,416,787	25,866,109	23,067,201	1,534,016	'	'	'	'	19,307,422	1,524,628	1,496,262
Net (loss) income per common share, basic	'	'	'	'	($3.90)	$6.70	($3.44)	($5.14)	'	'	'
Net (loss) income per common share, diluted	'	'	'	'	($3.90)	$0.11	($3.44)	($5.14)	'	'	'
Weighted-average shares outstanding, basic	'	'	'	'	1,532,633	1,529,442	1,518,753	1,517,465	'	'	'
Weighted-average shares outstanding, diluted	'	'	'	'	1,532,633	52,933,956	1,518,753	1,517,465	'	'	'

Subsequent_Events_Details

Subsequent Events (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Operating leases, future minimum payments due, total	$1,135
Subsequent Event [Member] | Current Extension on Facility [Member]	'
Operating leases, future minimum payments due, total	$100