Xencor (XNCR) 10-Q15 May 142014 Q1 Quarterly reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2014	Apr. 30, 2014
Document and Entity Information	'	'
Entity Registrant Name	'Xencor Inc	'
Entity Central Index Key	'0001326732	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	31,361,493
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets	'	'
Cash	$72,536	$77,975
Accounts receivable	511	59
Prepaid expenses and other current assets	159	60
Total current assets	73,206	78,094
Property and equipment	'	'
Computers, software and equipment	3,580	3,514
Furniture and fixtures	89	89
Leasehold improvements	3,081	3,081
Less accumulated depreciation and amortization	-6,410	-6,377
Property and equipment, net	340	307
Other assets	'	'
Patents, licenses, and other intangible assets, net	8,899	8,814
Other assets	50	100
Total other assets	8,949	8,914
Total assets	82,495	87,315
Current liabilities	'	'
Accounts payable	2,104	2,633
Accrued expenses	1,465	1,393
Current portion of deferred revenue	3,251	3,444
Current portion of capital lease obligations	7	9
Total current liabilities	6,827	7,479
Deferred revenue, less current portion	5,603	6,302
Capital lease obligations, less current portion	'	1
Total liabilities	12,430	13,782
Commitments and contingencies	'	'
Stockholders' equity	'	'
Common stock, $0.01 par value: 200,000,000 authorized shares at March 31, 2014 and December 31, 2013; 31,361,444 issued and outstanding at March 31, 2014 and 31,354,467 issued and outstanding shares at December 31, 2013	314	314
Additional paid-in capital	301,073	300,790
Accumulated deficit	-231,322	-227,571
Total stockholders' equity	70,065	73,533
Total liabilities and stockholders' equity	$82,495	$87,315

Condensed_Balance_Sheets_Paren

Condensed Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Condensed Balance Sheets	'	'
Common Stock, par value (in dollars per share)	$0.01	$0.01
Common Stock, shares authorized	200,000,000	200,000,000
Common Stock, shares issued	31,361,444	31,354,467
Common Stock, shares outstanding	31,361,444	31,354,467

Condensed_Statements_of_Operat

Condensed Statements of Operations (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenue	'	'
Collaborations, licenses and milestones	$2,184	$1,345
Operating expenses	'	'
Research and development	4,228	4,560
General and administrative	1,723	746
Total operating expenses	5,951	5,306
Loss from operations	-3,767	-3,961
Other income (expenses)	'	'
Interest income	18	1
Interest expense	-2	-661
Other (expense) income	'	9
Total other income (expense), net	16	-651
Net loss	($3,751)	($4,612)
Basic and diluted net loss per common share (in dollars per share)	($0.12)	($63.78)
Weighted average shares used to compute basic and diluted net loss per common share (in shares)	31,360,879	72,302

Condensed_Statements_of_Cash_F

Condensed Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities	'	'
Net loss	($3,751)	($4,612)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:	'	'
Depreciation and amortization	320	139
Stock-based compensation	278	5
Abandonment of capitalized intangible assets	10	168
Gain on disposal of assets	'	-9
Accrued interest on convertible promissory notes (See Note 3)	'	660
Changes in operating assets and liabilities:	'	'
Accounts receivable	-452	-172
Prepaid expenses and other current assets	-99	'
Other assets	50	'
Accounts payable	-529	1,610
Accrued expenses	72	-565
Deferred revenue	-892	4,422
Net cash (used in) provided by operating activities	-4,993	1,646
Cash flows from investing activities	'	'
Purchase of intangible assets	-382	-521
Purchase of property and equipment	-66	-36
Proceeds from sale of property and equipment	'	9
Net cash used in investing activities	-448	-548
Cash flows from financing activities	'	'
Proceeds from issuance of common stock upon exercise of stock awards	4	'
Payments on capital lease obligations	-2	-2
Net cash provided by (used in) financing activities	2	-2
Net increase (decrease) in cash	-5,439	1,096
Cash, beginning of period	77,975	2,312
Cash, end of period	72,536	3,408
Cash paid for:	'	'
Interest	$2	'

Description_of_Business

Description of Business	3 Months Ended
Description of Business	Mar. 31, 2014
Description of Business	'
Description of Business	'
	1. Description of Business

	Xencor, Inc. (we, us, our, or the Company) was incorporated in California in 1997 and reincorporated in Delaware in September 2004. We are a clinical-stage biopharmaceutical company focused on discovering and developing engineered monoclonal antibodies to treat severe and life-threatening diseases with unmet medical needs. We use our proprietary XmAb technology platform to create next-generation antibody product candidates designed to treat autoimmune and allergic diseases, cancer, and other conditions. Our engineered Fc domains, the XmAb technology, are applied to our pipeline of antibody-based drug candidates to increase immune inhibition, improve cytotoxicity, or extend half-life. We also enter into collaborations with pharmaceutical companies to allow them to use our XmAb technology in their drug development activities.

	Our operations are based in Monrovia, California and we operate in one segment.

	Unaudited Interim Financial Information

	The accompanying financial information as of March 31, 2014 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. December 31, 2013 balances were derived from the audited Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 filed with the Securities and Exchange Commission on March 31, 2104. The accompanying Condensed Balance Sheet does not include all the disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2013 included in the Company’s Annual Report on Form 10-K.

	Initial Public Offering

	We completed our initial public offering (IPO) in December 2013, pursuant to which we issued 14,639,500 shares of common stock which included shares we issued pursuant to our underwriters’ exercise of their over-allotment option, and received net proceeds of $72.5 million, after underwriting discounts, commissions and estimated offering expenses. In addition, in connection with the completion of our IPO, all then outstanding convertible preferred stock converted into common stock.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2014
Summary of Significant Accounting Policies	'
Summary of Significant Accounting Policies	'
	2. Summary of Significant Accounting Policies

	Use of Estimates

	The preparation of the financial statements in accordance with GAAP requires the Company to make estimates and judgments in certain circumstances that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures. In preparing these financial statements, management has made its best estimates and judgments of certain amounts included in the financial statements, giving due consideration to materiality. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, fair values of assets, convertible preferred stock and common stock, income taxes, pre-clinical study and clinical trial accruals and other contingencies. Management bases its estimates on historical experience or on various other assumptions that it believes to be reasonable under the circumstances. Actual results could materially differ from these estimates.

	Reverse Stock Split

	On November 1, 2013, the Company affected a 1 for 3.1 reverse stock split. All information in this report relating to the number of shares, price per share and per share amounts of stock prior to November 1, 2013 gives retroactive effect to the 1 for 3.1 reverse stock split of the Company’s stock.

	Research and Development Expenses

	Costs incurred in research and development activities are expensed as incurred, including expenses that may or may not be reimbursed under research and development collaboration agreements. Research and development costs include, but are not limited to, salaries, benefits, stock-based compensation, laboratory supplies and equipment, allocated overhead, fees for professional service providers and costs associated with product development efforts, including preclinical studies and clinical trials.

	The Company estimates preclinical study and clinical trial expenses based on the services performed, pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered.

	Fair Value of Financial Instruments

	Our financial instruments primarily consist of cash, trade accounts receivable, convertible promissory notes, accounts payable and accrued expenses. The fair value of cash and cash equivalents, trade accounts receivable, convertible promissory notes, accounts payable and accrued expenses closely approximate their carrying value due to their short maturities. The carrying amounts of convertible promissory notes approximate their fair value, as the interest rates, in consideration of the conversion feature, approximate the interest rates presently available to us.

	We determine the fair value of the principal amount of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:

	Level 1—Quoted prices in active markets for identical assets or liabilities;

	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and

	Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

	Level 1 assets consist of highly-liquid money market funds. There were no transfers between Level 1 and Level 2 assets during the periods presented.

	The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in millions):

			March 31, 2014						March 31, 2013
			Total						Total
			Fair Value			Level 1			Fair Value			Level 1

	Money Market Funds		$	—		$	—		$	3.3		$	3.3


	For disclosure purposes at March 31, 2014 and March 31, 2013 the fair value of the principal amount of our outstanding convertible promissory notes are classified within the hierarchy as follows (in millions):

			March 31, 2014						March 31, 2013
			Total						Total
			Fair Value			Level 3			Fair Value			Level 3

	Convertible Promissory Notes		$	—		$	—		$	15.1		$	15.1


	These convertible promissory notes were originally issued during 2009 and 2010. Considering 1) the lack of time value, 2) the absence of an established market for the convertible promissory notes, and, 3) our knowledge of the terms, rates, risk and returns provided by the convertible promissory notes as compared to financing available for privately-held biopharmaceutical companies, we determined that the carrying value of the convertible promissory notes approximates their fair value. There were no transfers between Level 3, Level 2 and, Level 1 during the periods presented.

	Net Loss Per Share of Common Stock

	We compute net loss per common share by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Potentially dilutive securities consisting of stock options, convertible preferred stock and convertible promissory notes are not included in the diluted net loss per common share calculation for all periods presented, because the inclusion of such shares would have had an antidilutive effect.

			Three Months Ended March 31,
			2014			2013
			(in thousands, except
			per share amounts)
	Basic and diluted numerator:
	Net loss attributable to common stockholders		$	(3,751	)	$	(4,612	)
	Denominator:
	Weighted-average common shares outstanding- basic and diluted		31,360,879			72,302
	Basic and diluted net loss per common share		$	(0.12	)	$	(63.78	)

For the three months ended March 31, 2014 and March 31, 2013, we excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive.

		As of
		March 31,
		2014		2013
		(in thousands)
Convertible preferred stock		—		12,189
Convertible promissory notes		—		2,845
Employee stock purchase plan shares		45		—
Options to purchase common stock		1,213		1,277
		1,258		16,311

Revenue Recognition

We have, to date, earned revenue from research collaborations, which may include research and development services, licenses of our internally-developed technologies, or a combination of both. We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer or access of technology has been completed or services have been rendered; our price to the customer is fixed or determinable and collectability is reasonably assured.

The terms of our licensing and research and development agreements include non-refundable upfront fees, licensing fees, contingent payment and contractual obligations for the achievement of pre-defined preclinical, clinical, regulatory and sales based events. The agreements also include royalties on sales of any commercialized products.

Multiple-Element Revenue Arrangements. Certain of our collaboration and license agreements represent multiple-element revenue arrangements. To account for such transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separate units for accounting purposes. We consider delivered items to be separate units of accounting if the delivered items have stand-alone value to the customer. If the delivered items are separate units we allocate the consideration received or due under the arrangement to the various elements based on each elements’ relative selling price.

Milestone Revenue. Our collaboration and license agreements generally include contingent contractual payments related to achievement of specific research, development and regulatory milestones and sales-based milestones that are based solely upon the performance of the licensor or collaborator. Research, development and regulatory contingent contractual payments and milestone payments are typically payable under our collaborations when our collaborator selects a compound, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based contingent contractual payments are typically payable when annual sales of a covered product reach specific levels.

We recognize any payment that is contingent upon the achievement of a substantive milestone entirely in the period in which the milestone is achieved. A milestone is defined as an event that can only be achieved based in whole or in part either on our performance, or the performance of our collaborators, or the occurrence of a specific outcome resulting from our past performance for which there is a substantive uncertainty at the date the arrangement is entered into that the event will be achieved.

Long-Lived Assets

Management reviews long-lived and certain identifiable intangibles for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Fair value for our long-lived assets is determined using the expected cash flows discounted at a rate commensurate with the risks involved.

Stock-Based Compensation

We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options and stock issued under our 2013 Employee Stock Purchase Plan (ESPP). Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value—based measurement of the award using the Black-Scholes method, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. We recorded stock-based compensation expense for stock-based awards to employees and directors of approximately $278,000 and $5,000 for the three months ended March 31, 2014 and 2013, respectively.

The expected term for purchases under the ESPP was based on the purchase periods included in the offering. The expected volatility is determined using historical volatilities of similar peer companies based on stock prices over a look-back period corresponding to the expected term. The risk-free interest rate was determined using the yield available for zero-coupon U.S. government issues with a remaining term equal to the expected term. The forfeiture rate was determined to be zero as there is insufficient historical pre-vesting forfeiture rate information since the inception of the plan. The Company has never paid a dividend, and as such, the dividend yield is zero. See Note 4 for further information on the ESPP.

Options granted to individual service providers that are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing method and are subject to periodic re-measurement over the period during which the services are rendered.

Concentrations of Risk

Cash is maintained at financial institutions and, at times, balances may exceed federally insured limits. Amounts on deposit in excess of federally insured limits at March 31, 2014 approximated $72.0 million.

A significant portion of our revenue was earned from four partners for the three months ended March 31, 2014 and from three partners for the three months ended March 31, 2013. The following table represents the amounts (in millions) and the percentage of all significant revenue earned in the periods indicated:

		Three Months Ended March 31,
		2014					2013
		Amounts			Percentages		Amounts			Percentages
Alexion		$	0.3		11.4	%	$	0.1		12.4	%
Amgen		0.6			25.6	%	0.6			41.5	%
CSL		0.7			32.5	%	0.6			43.7	%
Merck		0.5			22.9	%	—			—
Other		0.1			7.6	%	0.03			2.4	%


As of March 31, 2014, $0.5 million in accounts receivable was due from one partner; as of March 31, 2013, $0.5 million in accounts receivable was due from another partner.

Patents, Licenses, and Other Intangible Assets

The cost of acquiring licenses is capitalized and amortized on the straight-line basis over the shorter of the term of the license or its estimated economic life, ranging from five to 25 years. Third-party costs incurred for acquiring patents are capitalized. Capitalized costs are accumulated until the earlier of the period that a patent is issued or we abandon the patent claims. Cumulative capitalized patent costs are amortized on a straight-line basis from the date of issuance over the shorter of the patent term or the estimated useful economic life of the patent, ranging from 13 to 20 years. The carrying value of intangible assets is evaluated when indicators of impairment are identified. We review the license arrangements and the amortization period on a regular basis and adjust the carrying value or the amortization period of the licensed rights if there is evidence of a change in the carrying value or useful life of the asset.

Convertible_Promissory_Notes_a

Convertible Promissory Notes and Conversion of Convertible Preferred Stock	3 Months Ended
	Mar. 31, 2014
Convertible Promissory Notes and Conversion of Convertible Preferred Stock	'
Convertible Promissory Notes and Conversion of Convertible Preferred Stock	'
	3. Convertible Promissory Notes and Conversion of Convertible Preferred Stock

	As of March 31, 2013, the Company had $21.6 million in outstanding convertible promissory notes which included $15.1 million in principal and $6.5 million in accrued interest. The notes carried an accrued interest rate of 12.5% and included contingent redemption features which provided that the notes would convert into preferred stock upon certain liquidation or change of control events. During June 2013, the convertible promissory notes were exchanged for convertible preferred stock. In connection with the completion of the Company’s IPO in December 2013, all outstanding shares of convertible preferred stock converted into 16,620,274 shares of common stock.

Equity_Incentive_Plans

Equity Incentive Plans	3 Months Ended
Equity Incentive Plans	Mar. 31, 2014
Equity Incentive Plans	'
Equity Incentive Plans	'
	4. Equity Incentive Plans

	Our Board of Directors and the requisite stockholders previously approved the Amended and Restated 2000 Stock Incentive Plan, or the 2000 Plan, and the 2010 Equity Incentive Plan, or the 2010 Plan, and collectively with the 2000 Plan the Prior Plans. The 2000 Plan terminated August 2010. In November 2013, our Board of Directors and stockholders approved the 2013 Equity Incentive Plan, or the 2013 Plan. The 2013 Plan became effective as of December 3, 2013 the date of the Company’s IPO. As of December 2, 2013, we suspended the 2010 Plan and no additional awards may be granted under the 2010 Plan. Any shares of common stock covered by awards granted under the Prior Plans that terminate after December 2, 2013 by expiration, forfeiture, cancellation or other means without the issuance of such shares will be added to the 2013 Plan reserve.

	As of March 31, 2014, the total number of shares of common stock available for issuance under the 2013 Plan was 5,418,943, which includes 2,662,065 of common stock that were available for issuance under the Prior Plans as of the effective date of the 2013 Plan. Unless otherwise determined by the Board, beginning January 1, 2014, and continuing until the expiration of the 2013 Plan, the total number of shares of common stock available for issuance under the 2013 Plan will automatically increase annually on January 1 by 4% of the total number of issued and outstanding shares of common stock as of December 31 of the immediate preceding year. On January 1, 2014, the total number of shares of common stock available for issuance under the 2013 Plan was automatically increased by 1,254,179 shares, which number is included in the number of shares available for issuance above. As of March 31, 2014 715,500 options had been issued under the 2013 Plan.

	In November 2013, our Board of Directors and stockholders approved the 2013 Employee Stock Purchase Plan, or the ESPP, which became effective as of December 5, 2013. Under the ESPP our employees may elect to have between 1-15% of their compensation withheld to purchase Company stock at a discount. The ESPP has an initial two year term that includes four six month purchase periods and employee withholding amounts may be used to purchase Company stock during each six month purchase period. The total number of shares that can be purchased with the withholding amounts are based on the lower of 85% of the Company’s stock price at the initial offering date or, 85% of the Company’s stock price at each purchase date. We have reserved a total of 581,286 shares of common stock for issuance under the ESPP. Unless otherwise determined by our Board, beginning on January 1, 2014, and continuing until the expiration of the ESPP, the total number shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 621,814 shares of common stock. On January 1, 2014, the total number of shares of common stock available for issuance under the ESPP was automatically increased by 313,545 shares, which number is included in the number of shares reserved for issuance above. As of March 31, 2014, we have not issued any shares of common stock under the ESPP.

	The following table summarizes option activity under our 2013 Plan and related information:

				Weighted
				Average
		Number of		Exercise
		Shares subject		Price
		to outstanding		(Per
		options		Share)
	Balances at December 31, 2013	1,794,214		$	1.66
	Options granted	700,500		$	11.2
	Options forfeited	—		—
	Options exercised	(6,977	)	$	0.59
	Balance at March 31, 2014	2,487,737		$	4.34

	As of March 31, 2014, options to purchase 1,212,950 shares of common stock were outstanding that are vested and therefore exercisable with a weighted-average exercise price of $0.59 per share and a weighted-average remaining contractual life of 3.7 years. The aggregate intrinsic value of options outstanding was $18.4 million. The aggregate intrinsic value of outstanding options that are exercisable was $13.5 million and the intrinsic value of options exercised during the three months ended March 31, 2014 was $78,000. We calculate the intrinsic value as the difference between the exercise price of the options and the closing price of common stock of $11.73 per share as of March 31, 2014.

	Total employee, director and non-employee stock-based compensation expense recognized was as follows (in thousands):

		Three Months Ended
		March 31,
		2014			2013
	General and administrative	$	128		$	3
	Research and development	150			2
		$	278		$	5

	Weighted average fair value of options granted during the period ended March 31, 2014 was $7.44 per share; there were no options granted during the period ended March 31, 2013. We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following weighted average assumptions for the three months ended March 31, 2014 and 2013:

		Options				ESPP
		Three Months Ended March 31,				Three Months Ended March 31,
		2014		2013		2014		2013
	Expected term (years)	6		6		0.5-2.0		—
	Expected volatility	75.2	%	75.2-86.7	%	70.6	%	—
	Risk-free interest rate	2.0 1	%	2.19	%	0.07-0.46	%	—
	Expected dividend yield	0	%	0	%	0	%	—

	At March 31, 2014, the Company had $4.8 million of total unrecognized compensation expense, net of estimated forfeitures, related to outstanding stock options that will be recognized over the next 3.5 years.

Collaboration_Research_and_Lic

Collaboration Research and Licensing Agreements	3 Months Ended
Collaboration Research and Licensing Agreements	Mar. 31, 2014
Collaboration Research and Licensing Agreements	'
Collaboration Research and Licensing Agreements	'
	5. Collaboration Research and Licensing Agreements

	Following are a summary description of the arrangements that generated revenue in the three month periods ended March 31, 2014 and March 31, 2013.

	Amgen, Inc.

	In December 2010, we entered into a Collaboration and Option Agreement with Amgen, Inc. (Amgen), pursuant to which we agreed to collaborate with Amgen to research, develop and commercialize XmAb5871. Under the agreement, we granted to Amgen an option to acquire an exclusive license to research, develop, manufacture and commercialize XmAb5871. The term of the option began at the effective date of the Agreement and expires 90 days after delivery of the data from a Phase 2 proof-of-concept (POC) clinical trial. During the option period and prior to Amgen exercising its option under the agreement, we retain ownership of the compound and are responsible for all clinical development of the compound through completion of the Phase 2 POC clinical trial and delivery of the clinical study data for the POC clinical trial. We received a nonrefundable upfront payment of $11.0 million upon execution of the agreement. We are eligible to receive milestone payments through the option period and following the exercise of the option by Amgen, additional milestone payments and royalties. We determined that substantially all of the future milestones and related payments were substantive and contingent and we did not allocate any of the upfront consideration to the milestones.

	We determined that the arrangement is one with multiple deliverables and we identified the multiple elements at the inception of the agreement. We determined that the deliverables under the arrangement were the research and development services and the option to acquire the rights to XmAb5871. Since the option is a contingent and a substantive element, no portion of the upfront fee was allocated to it. The upfront payment was allocated to the research and development services and is being recognized ratably over the estimated service period to complete the Phase 2 POC trial and delivery of the clinical study reports to Amgen. We have estimated that the term of the service period to be 72 months from inception of the agreement through completion of the POC trial.

	During the first quarter of 2013, we initiated a Phase 1b clinical trial under the arrangement and we received a milestone payment of $2.0 million. We are recognizing that payment over the term in which service under the agreement relate.

	During the three months ended March 31, 2014 we recognized $0.6 million of revenue under this arrangement and during the three months ended March 31, 2013 we recognized $0.6 million of revenue under this arrangement. As of March 31, 2014 we have deferred revenue related to this agreement of $6.3 million.

	Merck Sharp & Dohme Corp.

	In July 2013, we entered into a License Agreement with Merck Sharp & Dohme Corp (Merck). Under the terms of the agreement, we provided Merck with a non-exclusive commercial license to certain patent rights to our Fc domains to apply to one of their compounds. We also provided Merck with contingent options to take additional non-exclusive commercial licenses. The contingent options provide Merck an opportunity to take non-exclusive commercial licenses at an amount less than the amount paid for the original license. The agreement provided for an upfront payment of $1.0 million and annual maintenance fees totaling $0.5 million. We are also eligible to receive future milestones and royalties as Merck advances the compound into clinical development.

	We determined that the deliverables under this agreement were the non-exclusive commercial license and the options. The options are considered substantive and contingent and no amount of the upfront payment was allocated to these options. We also determined that the future milestones and related payments were substantive and contingent and did not allocate any of the upfront payment to the milestones.

	In the first quarter of 2014, Merck initiated a Phase 1 clinical trial which triggered a milestone payment to us. During the three months ended March 31, 2014 we recognized $0.5 million of revenue under this arrangement. As of March 31, 2014 there is no deferred revenue related to this arrangement.

	Alexion Pharmaceuticals, Inc.

	In January 2013, we entered into an option and license agreement with Alexion Pharmaceuticals, Inc. (Alexion). Under the terms of the agreement, we granted to Alexion an exclusive research license, with limited sublicensing rights, to make and use our Xtend technology to evaluate and advance compounds against six different target programs during a five-year research term under the agreement, up to completion of the first multi-dose human clinical trial for each target compound. Alexion may extend the research term for an additional three years upon written notice to us and payment of an extension fee of $2.0 million. Alexion is responsible for conducting all research and development activities under the agreement at its own expense.

	In addition, we granted to Alexion an exclusive option, on a target-by-target basis, to obtain an exclusive commercial, worldwide, royalty-bearing license, with sublicensing rights, under our Xtend technology to develop and commercialize products that contain the target for which the option is exercised. In order to exercise this option, Alexion must pay a $4.0 million option fee with respect to each target for which the option is exercised. Alexion may exercise this option at any time during the research term.

	Under the agreement, we received an upfront payment of $3.0 million. Alexion is also required to pay an annual maintenance fee of $0.5 million during the research term of the agreement and $1.0 million during any extension of the research term. In addition, if certain development, regulatory and commercial milestones are achieved, we are eligible to receive up to $66.5 million for the first product to achieve such milestones on a target-by-target basis. If licensed products are successfully commercialized, we are also entitled to receive royalties based on a percentage of net sales of such products sold by Alexion, its affiliates or its sublicensees, which percentage is in the low single digits.

	During the three months ended March 31, 2014 we recognized $0.3 million of revenue under this arrangement and during the three months ended March 31, 2013 we recognized $0.1 million of revenue under this arrangement. As of March 31, 2014 we have deferred revenue related to this arrangement of $2.3 million.

	CSL Limited

	In 2009, we entered into a Research License and Commercialization Agreement with CSL Limited (CSL). Under the agreement, we provided CSL with a research license to one of our technologies and up to five commercial options. The upfront payment of $0.75 million received at inception and the annual research license renewal payments are being recognized as revenue ratably over the five-year term of the research license. We identified the deliverables under the agreement at inception as the five-year research licenses and options to acquire commercial licenses. We determined that the deliverables under this agreement were the non-exclusive commercial license and the options. The options are considered substantive and contingent and no amount of the upfront payment was allocated to these options. We also determined that the future milestones and related payments were substantive and contingent and did not allocate any of the upfront payment to the milestones. The upfront payment and the annual license fees were allocated to the research license and are being recognized into income over the research term and payments for commercial options are being recognized in the period the commercial option was exercised since the options were contingent and substantive.

	In May 2013, we entered into an amendment to a February 2009 Research License and Commercialization Agreement with CSL, which eliminated a contingent milestone payment requirement and reduced the royalty rate on net sales for the licensed product CSL362. The amendment provided for a payment upon signing of $2.5 million. We determined that the amendment was a material modification to the original agreement and evaluated the remaining deliverables at the date of the amendment. We determined that the remaining deliverables were the research license which expired in February 2014 and four additional options to take commercial licenses through the term of the research period. The options are considered to be substantive and contingent and we did not allocate any of the proceeds received in the amendment to the options. The amendment proceeds are being recognized into income over the remaining period of the research term.

	During the three months ended March 31, 2014 we recognized $0.7 million of revenue under this arrangement and during the three months ended March 31, 2013 we recognized $0.1 million of revenue under this arrangement. As of March 31, 2014 we have no deferred revenue related to this arrangement.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Polices)	3 Months Ended
Summary of Significant Accounting Policies (Polices)	Mar. 31, 2014
Summary of Significant Accounting Policies	'
Use of Estimates	'
	Use of Estimates

	The preparation of the financial statements in accordance with GAAP requires the Company to make estimates and judgments in certain circumstances that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures. In preparing these financial statements, management has made its best estimates and judgments of certain amounts included in the financial statements, giving due consideration to materiality. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, fair values of assets, convertible preferred stock and common stock, income taxes, pre-clinical study and clinical trial accruals and other contingencies. Management bases its estimates on historical experience or on various other assumptions that it believes to be reasonable under the circumstances. Actual results could materially differ from these estimates.
Reverse Stock Split	'
	Reverse Stock Split

	On November 1, 2013, the Company affected a 1 for 3.1 reverse stock split. All information in this report relating to the number of shares, price per share and per share amounts of stock prior to November 1, 2013 gives retroactive effect to the 1 for 3.1 reverse stock split of the Company’s stock.
Research and Development Expenses	'
	Research and Development Expenses

	Costs incurred in research and development activities are expensed as incurred, including expenses that may or may not be reimbursed under research and development collaboration agreements. Research and development costs include, but are not limited to, salaries, benefits, stock-based compensation, laboratory supplies and equipment, allocated overhead, fees for professional service providers and costs associated with product development efforts, including preclinical studies and clinical trials.

	The Company estimates preclinical study and clinical trial expenses based on the services performed, pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered.
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments

	Our financial instruments primarily consist of cash, trade accounts receivable, convertible promissory notes, accounts payable and accrued expenses. The fair value of cash and cash equivalents, trade accounts receivable, convertible promissory notes, accounts payable and accrued expenses closely approximate their carrying value due to their short maturities. The carrying amounts of convertible promissory notes approximate their fair value, as the interest rates, in consideration of the conversion feature, approximate the interest rates presently available to us.

	We determine the fair value of the principal amount of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:

	Level 1—Quoted prices in active markets for identical assets or liabilities;

	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and

	Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

	Level 1 assets consist of highly-liquid money market funds. There were no transfers between Level 1 and Level 2 assets during the periods presented.

	The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in millions):

		March 31, 2014						March 31, 2013
		Total						Total
		Fair Value			Level 1			Fair Value			Level 1

	Money Market Funds	$	—		$	—		$	3.3		$	3.3


	For disclosure purposes at March 31, 2014 and March 31, 2013 the fair value of the principal amount of our outstanding convertible promissory notes are classified within the hierarchy as follows (in millions):

		March 31, 2014						March 31, 2013
		Total						Total
		Fair Value			Level 3			Fair Value			Level 3

	Convertible Promissory Notes	$	—		$	—		$	15.1		$	15.1


	These convertible promissory notes were originally issued during 2009 and 2010. Considering 1) the lack of time value, 2) the absence of an established market for the convertible promissory notes, and, 3) our knowledge of the terms, rates, risk and returns provided by the convertible promissory notes as compared to financing available for privately-held biopharmaceutical companies, we determined that the carrying value of the convertible promissory notes approximates their fair value. There were no transfers between Level 3, Level 2 and, Level 1 during the periods presented.
Net Loss Per Share of Common Stock	'
	Net Loss Per Share of Common Stock

	We compute net loss per common share by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Potentially dilutive securities consisting of stock options, convertible preferred stock and convertible promissory notes are not included in the diluted net loss per common share calculation for all periods presented, because the inclusion of such shares would have had an antidilutive effect.

		Three Months Ended March 31,
		2014			2013
		(in thousands, except
		per share amounts)
	Basic and diluted numerator:
	Net loss attributable to common stockholders	$	(3,751	)	$	(4,612	)
	Denominator:
	Weighted-average common shares outstanding- basic and diluted	31,360,879			72,302
	Basic and diluted net loss per common share	$	(0.12	)	$	(63.78	)

	For the three months ended March 31, 2014 and March 31, 2013, we excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive.

		As of
		March 31,
		2014		2013
		(in thousands)
	Convertible preferred stock	—		12,189
	Convertible promissory notes	—		2,845
	Employee stock purchase plan shares	45		—
	Options to purchase common stock	1,213		1,277
		1,258		16,311
Revenue Recognition	'
	Revenue Recognition

	We have, to date, earned revenue from research collaborations, which may include research and development services, licenses of our internally-developed technologies, or a combination of both. We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer or access of technology has been completed or services have been rendered; our price to the customer is fixed or determinable and collectability is reasonably assured.

	The terms of our licensing and research and development agreements include non-refundable upfront fees, licensing fees, contingent payment and contractual obligations for the achievement of pre-defined preclinical, clinical, regulatory and sales based events. The agreements also include royalties on sales of any commercialized products.

	Multiple-Element Revenue Arrangements. Certain of our collaboration and license agreements represent multiple-element revenue arrangements. To account for such transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separate units for accounting purposes. We consider delivered items to be separate units of accounting if the delivered items have stand-alone value to the customer. If the delivered items are separate units we allocate the consideration received or due under the arrangement to the various elements based on each elements’ relative selling price.

	Milestone Revenue. Our collaboration and license agreements generally include contingent contractual payments related to achievement of specific research, development and regulatory milestones and sales-based milestones that are based solely upon the performance of the licensor or collaborator. Research, development and regulatory contingent contractual payments and milestone payments are typically payable under our collaborations when our collaborator selects a compound, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based contingent contractual payments are typically payable when annual sales of a covered product reach specific levels.

	We recognize any payment that is contingent upon the achievement of a substantive milestone entirely in the period in which the milestone is achieved. A milestone is defined as an event that can only be achieved based in whole or in part either on our performance, or the performance of our collaborators, or the occurrence of a specific outcome resulting from our past performance for which there is a substantive uncertainty at the date the arrangement is entered into that the event will be achieved.
Long-Lived Assets	'
	Long-Lived Assets

	Management reviews long-lived and certain identifiable intangibles for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Fair value for our long-lived assets is determined using the expected cash flows discounted at a rate commensurate with the risks involved.
Stock-Based Compensation	'
	Stock-Based Compensation

	We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options and stock issued under our 2013 Employee Stock Purchase Plan (ESPP). Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value—based measurement of the award using the Black-Scholes method, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. We recorded stock-based compensation expense for stock-based awards to employees and directors of approximately $278,000 and $5,000 for the three months ended March 31, 2014 and 2013, respectively.

	The expected term for purchases under the ESPP was based on the purchase periods included in the offering. The expected volatility is determined using historical volatilities of similar peer companies based on stock prices over a look-back period corresponding to the expected term. The risk-free interest rate was determined using the yield available for zero-coupon U.S. government issues with a remaining term equal to the expected term. The forfeiture rate was determined to be zero as there is insufficient historical pre-vesting forfeiture rate information since the inception of the plan. The Company has never paid a dividend, and as such, the dividend yield is zero. See Note 4 for further information on the ESPP.

	Options granted to individual service providers that are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing method and are subject to periodic re-measurement over the period during which the services are rendered.
Concnetrations of Risk	'
	Concentrations of Risk

	Cash is maintained at financial institutions and, at times, balances may exceed federally insured limits. Amounts on deposit in excess of federally insured limits at March 31, 2014 approximated $72.0 million.

	A significant portion of our revenue was earned from four partners for the three months ended March 31, 2014 and from three partners for the three months ended March 31, 2013. The following table represents the amounts (in millions) and the percentage of all significant revenue earned in the periods indicated:

		Three Months Ended March 31,
		2014					2013
		Amounts			Percentages		Amounts			Percentages
	Alexion	$	0.3		11.4	%	$	0.1		12.4	%
	Amgen	0.6			25.6	%	0.6			41.5	%
	CSL	0.7			32.5	%	0.6			43.7	%
	Merck	0.5			22.9	%	—			—
	Other	0.1			7.6	%	0.03			2.4	%


	As of March 31, 2014, $0.5 million in accounts receivable was due from one partner; as of March 31, 2013, $0.5 million in accounts receivable was due from another partner.
Patents, Licenses, and Other Intangible Assets	'
	Patents, Licenses, and Other Intangible Assets

	The cost of acquiring licenses is capitalized and amortized on the straight-line basis over the shorter of the term of the license or its estimated economic life, ranging from five to 25 years. Third-party costs incurred for acquiring patents are capitalized. Capitalized costs are accumulated until the earlier of the period that a patent is issued or we abandon the patent claims. Cumulative capitalized patent costs are amortized on a straight-line basis from the date of issuance over the shorter of the patent term or the estimated useful economic life of the patent, ranging from 13 to 20 years. The carrying value of intangible assets is evaluated when indicators of impairment are identified. We review the license arrangements and the amortization period on a regular basis and adjust the carrying value or the amortization period of the licensed rights if there is evidence of a change in the carrying value or useful life of the asset.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	3 Months Ended
Summary of Significant Accounting Policies (Tables)	Mar. 31, 2014
Summary of Significant Accounting Policies	'
Schedule of assets recorded at fair value	'
	The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in millions):

		March 31, 2014						March 31, 2013
		Total						Total
		Fair Value			Level 1			Fair Value			Level 1

	Money Market Funds	$	—		$	—		$	3.3		$	3.3

Schedule of the fair value of the principal amount of outstanding convertible promissory notes	'
	For disclosure purposes at March 31, 2014 and March 31, 2013 the fair value of the principal amount of our outstanding convertible promissory notes are classified within the hierarchy as follows (in millions):

		March 31, 2014						March 31, 2013
		Total						Total
		Fair Value			Level 3			Fair Value			Level 3

	Convertible Promissory Notes	$	—		$	—		$	15.1		$	15.1

Schedule of calculation of diluted loss per share	'


		Three Months Ended March 31,
		2014			2013
		(in thousands, except
		per share amounts)
	Basic and diluted numerator:
	Net loss attributable to common stockholders	$	(3,751	)	$	(4,612	)
	Denominator:
	Weighted-average common shares outstanding- basic and diluted	31,360,879			72,302
	Basic and diluted net loss per common share	$	(0.12	)	$	(63.78	)
Schedule of securities excluded from the calculation of diluted net loss per share as the effect would have been antidilutive	'


		As of
		March 31,
		2014		2013
		(in thousands)
	Convertible preferred stock	—		12,189
	Convertible promissory notes	—		2,845
	Employee stock purchase plan shares	45		—
	Options to purchase common stock	1,213		1,277
		1,258		16,311
Schedule of percentage of all significant revenue earned	'
	The following table represents the amounts (in millions) and the percentage of all significant revenue earned in the periods indicated:

		Three Months Ended March 31,
		2014					2013
		Amounts			Percentages		Amounts			Percentages
	Alexion	$	0.3		11.4	%	$	0.1		12.4	%
	Amgen	0.6			25.6	%	0.6			41.5	%
	CSL	0.7			32.5	%	0.6			43.7	%
	Merck	0.5			22.9	%	—			—
	Other	0.1			7.6	%	0.03			2.4	%

Equity_Incentive_Plans_Tables

Equity Incentive Plans (Tables)	3 Months Ended
Equity Incentive Plans (Tables)	Mar. 31, 2014
Equity Incentive Plans	'
Summary of stock option activity	'


				Weighted
				Average
		Number of		Exercise
		Shares subject		Price
		to outstanding		(Per
		options		Share)
	Balances at December 31, 2013	1,794,214		$	1.66
	Options granted	700,500		$	11.2
	Options forfeited	—		—
	Options exercised	(6,977	)	$	0.59
	Balance at March 31, 2014	2,487,737		$	4.34
Schedule of total employee, director and non-employee stock-based compensation expense recognized	'
	Total employee, director and non-employee stock-based compensation expense recognized was as follows (in thousands):

		Three Months Ended
		March 31,
		2014			2013
	General and administrative	$	128		$	3
	Research and development	150			2
		$	278		$	5
Schedule of weighted average assumptions used for estimation of fair value of stock options	'


		Options				ESPP
		Three Months Ended March 31,				Three Months Ended March 31,
		2014		2013		2014		2013
	Expected term (years)	6		6		0.5-2.0		—
	Expected volatility	75.2	%	75.2-86.7	%	70.6	%	—
	Risk-free interest rate	2.0 1	%	2.19	%	0.07-0.46	%	—
	Expected dividend yield	0	%	0	%	0	%	—

Description_of_Business_Detail

Description of Business (Details) (USD $)	1 Months Ended	3 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2014
	Dec. 31, 2013	item
Description of Business	'	'
Number of operating segments	'	1
Initial Public Offering	'	'
Common stock sold under initial public offering (in shares)	14,639,500	'
Net proceeds received from initial public offering	$72.50	'

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details) (USD $)	0 Months Ended
	Nov. 01, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Reverse Stock Split and Conversion of Preferred Stock	'	'	'	'
Reverse stock split ratio	3.1	'	'	'
Fair Value of Financial Instruments	'	'	'	'
Transfers from level 1 to level 2	'	$0	$0	$0
Transfers from level 2 to level 1	'	0	0	0
Fair value of financial instruments	'	'	'	'
Transfers between Level 3, Level 2 and, Level 1	'	0	'	0
Total Fair Value \| Convertible Promissory Notes	'	'	'	'
Fair value of financial instruments	'	'	'	'
Liabilities recorded at fair value	'	'	'	15,100,000
Total Fair Value \| Money Market Funds	'	'	'	'
Fair value of financial instruments	'	'	'	'
Assets recorded at fair value	'	'	'	3,300,000
Level 1 \| Money Market Funds	'	'	'	'
Fair value of financial instruments	'	'	'	'
Assets recorded at fair value	'	'	'	3,300,000
Level 3 \| Convertible Promissory Notes	'	'	'	'
Fair value of financial instruments	'	'	'	'
Liabilities recorded at fair value	'	'	'	$15,100,000

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Basic and diluted numerator:	'	'
Net loss attributable to common stockholders	($3,751,000)	($4,612,000)
Denominator:	'	'
Weighted-average common shares outstanding- basic and diluted	31,360,879	72,302
Basic and diluted net loss per common share (in dollars per share)	($0.12)	($63.78)
Outstanding potentially dilutive securities have been excluded from the computations of diluted net loss per common share	'	'
Anti-dilutive securities (in shares)	1,258,000	16,311,000
Stock-Based Compensation	'	'
Stock-based compensation expense	$278,000	$5,000
Forfeiture rate (as a percent)	0.00%	'
Convertible preferred stock	'	'
Outstanding potentially dilutive securities have been excluded from the computations of diluted net loss per common share	'	'
Anti-dilutive securities (in shares)	'	12,189,000
Convertible Promissory Notes	'	'
Outstanding potentially dilutive securities have been excluded from the computations of diluted net loss per common share	'	'
Anti-dilutive securities (in shares)	'	2,845,000
Employee stock purchase plan shares	'	'
Outstanding potentially dilutive securities have been excluded from the computations of diluted net loss per common share	'	'
Anti-dilutive securities (in shares)	45,000	'
Options	'	'
Outstanding potentially dilutive securities have been excluded from the computations of diluted net loss per common share	'	'
Anti-dilutive securities (in shares)	1,213,000	1,277,000

Summary_of_Significant_Account5

Summary of Significant Accounting Policies (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Concentrations of Risk	'	'	'
Amounts on deposit in excess of federally insured limits approximately	$72,000,000	'	'
Concentrations of risk	'	'	'
Amounts	2,184,000	1,345,000	'
Accounts receivable	511,000	'	59,000
Revenue \| Customers	'	'	'
Concentrations of risk	'	'	'
Number of customers	4	3	'
Revenue \| Customers \| Alexion	'	'	'
Concentrations of risk	'	'	'
Amounts	300,000	100,000	'
Concentration risk percentage	11.40%	12.40%	'
Revenue \| Customers \| Amgen	'	'	'
Concentrations of risk	'	'	'
Amounts	600,000	600,000	'
Concentration risk percentage	25.60%	41.50%	'
Revenue \| Customers \| CSL	'	'	'
Concentrations of risk	'	'	'
Amounts	700,000	600,000	'
Concentration risk percentage	32.50%	43.70%	'
Revenue \| Customers \| Merck	'	'	'
Concentrations of risk	'	'	'
Amounts	500,000	'	'
Concentration risk percentage	22.90%	'	'
Revenue \| Customers \| Other	'	'	'
Concentrations of risk	'	'	'
Amounts	100,000	30,000	'
Concentration risk percentage	7.60%	2.40%	'
Accounts receivable \| Credit concentration	'	'	'
Concentrations of risk	'	'	'
Number of customers	1	'	'
Accounts receivable	$500,000	$500,000	'

Summary_of_Significant_Account6

Summary of Significant Accounting Policies (Details 4)	3 Months Ended
Summary of Significant Accounting Policies (Details 4)	Mar. 31, 2014
Acquired licenses \| Minimum	'
Patents, licenses, and other intangible assets	'
Estimated economic life	'5 years
Acquired licenses \| Maximum	'
Patents, licenses, and other intangible assets	'
Estimated economic life	'25 years
Patents \| Minimum	'
Patents, licenses, and other intangible assets	'
Estimated economic life	'13 years
Patents \| Maximum	'
Patents, licenses, and other intangible assets	'
Estimated economic life	'20 years

Convertible_Promissory_Notes_a1

Convertible Promissory Notes and Conversion of Convertible Preferred Stock (Details) (USD $)	1 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013
Convertible Promissory Notes	'
Shares of common stock issued for conversion of convertible preferred stock	16,620,274
Convertible Promissory Notes	'
Convertible Promissory Notes	'
Outstanding debt	21.6
Principal amount	15.1
Accrued interest	6.5
Accrued interest rate	12.50%

Equity_Incentive_Plans_Details

Equity Incentive Plans (Details) (USD $)	3 Months Ended		0 Months Ended		3 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Jan. 02, 2014	Mar. 31, 2014	Mar. 31, 2014	Dec. 03, 2013	Jan. 02, 2014	Dec. 05, 2013	Mar. 31, 2014	Dec. 05, 2013	Dec. 05, 2013
	Options	Options	The 2013 Plan	The 2013 Plan	The 2013 Plan	Prior Plans	ESPP	ESPP	ESPP	ESPP	ESPP
					Options			item		Minimum	Maximum
Stock-based compensation	'	'	'	'	'	'	'	'	'	'	'
Total number of shares of common stock available for issuance	'	'	'	5,418,943	'	2,662,065	'	'	581,286	'	'
Annual percentage increase in shares of common stock available for issuance	'	'	4.00%	'	'	'	1.00%	'	'	'	'
Increase in shares of common stock available for issuance (in shares)	'	'	1,254,179	'	'	'	313,545	'	'	'	'
Awards issued under the plan (in shares)	'	'	'	'	715,500	'	'	'	'	'	'
Percentage of employee's compensation withheld to purchase stock at a discount	'	'	'	'	'	'	'	'	'	1.00%	15.00%
Life of options	'	'	'	'	'	'	'	'2 years	'	'	'
Number of six month purchase periods	'	'	'	'	'	'	'	4	'	'	'
Purchase period	'	'	'	'	'	'	'	'6 months	'	'	'
Percentage of the entity's stock price at the initial offering date	'	'	'	'	'	'	'	85.00%	'	'	'
Purchase price as percentage of fair market value of the stock	'	'	'	'	'	'	'	85.00%	'	'	'
Annual increase in shares of common stock available for issuance (in shares)	'	'	'	'	'	'	621,814	'	'	'	'
Number of Shares subject to outstanding options	'	'	'	'	'	'	'	'	'	'	'
Balance at the beginning of the period (in shares)	1,794,214	'	'	'	'	'	'	'	'	'	'
Options granted (in shares)	700,500	0	'	'	'	'	'	'	'	'	'
Options exercised (in shares)	-6,977	'	'	'	'	'	'	'	'	'	'
Balance at the end of the period (in shares)	2,487,737	'	'	'	'	'	'	'	'	'	'
Weighted Average Exercise Price (per share)	'	'	'	'	'	'	'	'	'	'	'
Balance at the beginning of the period (in dollars per share)	$1.66	'	'	'	'	'	'	'	'	'	'
Options granted (in dollars per share)	$11.20	'	'	'	'	'	'	'	'	'	'
Options exercised (in dollars per share)	$0.59	'	'	'	'	'	'	'	'	'	'
Balance at the end of the period (in dollars per share)	$4.34	'	'	'	'	'	'	'	'	'	'
Awards exercisable (in shares)	1,212,950	'	'	'	'	'	'	'	'	'	'
Weighted-average remaining contractual life of awards exercisable	'3 years 8 months 12 days	'	'	'	'	'	'	'	'	'	'
Aggregate intrinsic value of options outstanding	$18,400,000	'	'	'	'	'	'	'	'	'	'
Aggregate intrinsic value of options exercisable	13,500,000	'	'	'	'	'	'	'	'	'	'
Intrinsic value of options exercised	$78,000	'	'	'	'	'	'	'	'	'	'
Closing price of common stock (in dollars per share)	$11.73	'	'	'	'	'	'	'	'	'	'

Equity_Incentive_Plans_Details1

Equity Incentive Plans (Details 2) (USD $)	3 Months Ended
Equity Incentive Plans (Details 2) (USD $)	Mar. 31, 2014	Mar. 31, 2013
Employee, director and non-employee stock-based compensation expense recognized	'	'
Total employee, director and non-employee stock-based compensation expense	$278,000	$5,000
Options	'	'
Employee, director and non-employee stock-based compensation expense recognized	'	'
Weighted average fair value of options granted (in dollars per share)	$7.44	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected term (years)	'6 years	'6 years
Expected volatility (as a percent)	75.20%	'
Risk-free interest rate (as a percent)	2.01%	2.19%
Expected dividend yield (as a percent)	0.00%	0.00%
Total unrecognized compensation expense, net of estimated forfeitures	4,800,000	'
Period to recognize total unrecognized compensation expense	'3 years 6 months	'
Options \| Minimum	'	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected volatility (as a percent)	'	75.20%
Options \| Maximum	'	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected volatility (as a percent)	'	86.70%
ESPP	'	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected volatility (as a percent)	70.60%	'
Expected dividend yield (as a percent)	0.00%	'
ESPP \| Minimum	'	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected term (years)	'6 months	'
Risk-free interest rate (as a percent)	0.07%	'
ESPP \| Maximum	'	'
Weighted average assumptions for estimated fair value of employee stock options	'	'
Expected term (years)	'2 years	'
Risk-free interest rate (as a percent)	0.46%	'
General and administrative	'	'
Employee, director and non-employee stock-based compensation expense recognized	'	'
Total employee, director and non-employee stock-based compensation expense	128,000	3,000
Research and development	'	'
Employee, director and non-employee stock-based compensation expense recognized	'	'
Total employee, director and non-employee stock-based compensation expense	$150,000	$2,000

Collaboration_Research_and_Lic1

Collaboration Research and Licensing Agreements (Details) (USD $)

3 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2010

Mar. 31, 2014

Mar. 31, 2013

Jul. 31, 2013

Mar. 31, 2014

Jan. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Jan. 31, 2013

Dec. 31, 2009

31-May-13

Mar. 31, 2014

Mar. 31, 2013

Collaboration and Option Agreement

License Agreement

Option and license agreement

2009 Research License and Commercialization Agreement

May 2013 Research License and Commercialization Agreement

Amgen, Inc.

Merck Sharp & Dohme Corp.

Alexion Pharmaceuticals, Inc.

CSL Limited

item

Maximum

item

Maximum

item

Collaboration research and licensing agreements

Option term after delivery of the data from a Phase 2 proof-of-concept (POC) clinical trial

'90 days

Nonrefundable upfront payment

$11,000,000

$1,000,000

$3,000,000

$750,000

$2,500,000

Annual maintenance fees

500,000

Estimated term of service period of research and development services

'72 months

Portion of nonrefundable upfront payment allocated to option

Milestone payment received

2,000,000

Revenue recognized

2,184,000

1,345,000

600,000

500,000

300,000

100,000

700,000

100,000

Deferred revenue

6,300,000

2,300,000

Number of different target programs

Research license term

'5 years

Additional research term

'3 years

Extension fee

2,000,000

Annual maintenance fees payable during any extension of research term

1,000,000

Option fee

4,000,000

Milestone payment to be received for first product upon achievement of certain development, regulatory and commercial milestones

$66,500,000

Number of technologies to which research license is provided

Number of commercial options