Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Collaboration revenue	$ 25,031	$ 19,792
Research and license fees	390	389	340
Total revenue	25,421	20,181	340
Operating expenses:
Research and development	62,574	31,002	17,210
General and administrative	23,227	14,126	6,846
Change in fair value of contingent consideration	246
Total operating expenses	86,047	45,128	24,056
Loss from operations	(60,626)	(24,947)	(23,716)
Other income (expense), net:
Interest income	152	29	5
Foreign currency gains (losses)	(163)	37	13
Re-measurement of warrants		(440)	28
Other income	131
Total other income (expense), net	120	(374)	46
Loss before income taxes	(60,506)	(25,321)	(23,670)
Benefit from income taxes	11,797
Net loss	(48,709)	(25,321)	(23,670)
Other comprehensive loss:
Unrealized loss on available-for-sale securities, net of tax	(71)		(1)
Total other comprehensive loss	(71)		(1)
Comprehensive loss	(48,780)	(25,321)	(23,671)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(48,709)	(25,321)	(23,670)
Accretion and dividends on convertible preferred stock			(3,057)
Gain on extinguishment of convertible preferred stock			23,114
Net loss applicable to common stockholders	$ (48,709)	$ (25,321)	$ (3,613)
Net loss per share applicable to common stockholders - basic and diluted:	$ (1.83)	$ (2.02)	$ (13.79)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	26,546	12,555	262