Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Summary of Fair Value Measurement Financial Assets

Financial assets measured at fair value on a recurring basis were as follows (in thousands):



	Fair Value Measurement at December 31, 2016
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	46,781	$	46,781	$	—	$	—
U.S Treasury securities	8,826		—		8,826		—
Government-sponsored enterprises	29,759		—		29,759		—
Corporate debt securities	166,300		—		166,300		—
Total assets measured at fair value ^(a)	$	251,666	$	46,781	$	204,885	$	—

(a) Total assets measured at fair value at December 31, 2016 includes approximately $50.8 million reported in cash and cash equivalents on the balance sheet.



	Fair Value Measurement at December 31, 2015
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	62,353	$	62,353	$	—	$	—
U.S Treasury securities	9,348		—		9,348		—
Government-sponsored enterprises	41,202		—		41,202		—
Corporate debt securities	137,928		—		137,928		—
Total assets measured at fair value ^(a)	$	250,831	$	62,353	$	188,478	$	—

(a) Total assets measured at fair value at December 31, 2015 includes approximately $108.0 million reported in cash and cash equivalents on the balance sheet.

Estimated Useful Lives

Depreciation is computed using the straight-line method over the following estimated useful lives:



Computer equipment	3 years
Software	3 years
Furniture	10 years
Laboratory and office equipment	5 years
Leasehold improvements	Shorter of lease term or useful life

Computation of Basic and Diluted Loss Per Common Share

Basic and diluted loss per common share is computed as follows (in thousands except share and per share data):



	Year Ended December 31,
	2016			2015			2014
Numerator:
Net loss used for calculation of basic and diluted EPS	$	(58,528	)	$	(20,140	)	$	(38,313	)

Denominator:
Weighted average shares outstanding, basic	34,685,274			31,801,645			27,384,990
Effect of dilutive securities:
Stock options and restricted stock units	—			—			—

Weighted average shares outstanding, diluted	34,685,274			31,801,645			27,384,990
Net loss per share, basic and diluted	$	(1.69	)	$	(0.63	)	$	(1.40	)

Schedule of Antidilutive Securities Excluded from the Calculation of Diluted Loss Per Share

The following common stock equivalents were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive:



	Year Ended December 31,
	2016	2015	2014
Stock options	1,394,608	1,955,398	2,094,904

Customer Concentration Risk

Summary of Percentage of Customer Concentration

The following table includes those collaborators that represent more than 10% of total revenue earned in the periods indicated:



	Year Ended December 31,
	2016		2015		2014
Janssen Biotech, Inc. (Janssen)	85	%	72	%	*
Les Laboratoires Servier and Institut de Reserches Servier (collectively, Servier)	*		*		36	%
Boehringer Ingelheim GmbH (Boehringer)	*		12	%	29	%
Takeda Pharmaceutical Company Limited (Takeda)	*		*		17	%
Gilead Sciences, Inc. (Gilead)	*		*		11	%

The following table includes those collaborators that represent more than 10% of accounts receivable at the date indicated:



	December 31,
	2016		2015
Janssen	40	%	39	%
U.S. government	19	%	20	%
Servier	31	%	14	%
Takeda	*		14	%
Eli Lilly	*		13	%

* Balance is less than 10%