Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Collaboration revenue	$ 14,079	$ 25,031	$ 19,792
Research and license fees		390	389
Total revenue	14,079	25,421	20,181
Operating expenses:
Research and development	134,038	62,574	31,002
General and administrative	46,209	23,227	14,126
Change in fair value of contingent consideration	2,869	246
Total operating expenses	183,116	86,047	45,128
Loss from operations	(169,037)	(60,626)	(24,947)
Other income (expense), net:
Interest income, net	1,591	152	29
Other income (expense), net	723	(32)	(403)
Total other income (expense), net	2,314	120	(374)
Loss before income taxes	(166,723)	(60,506)	(25,321)
Income tax (expense) benefit	(60)	11,797
Net loss	$ (166,783)	$ (48,709)	$ (25,321)
Net loss per share - basic and diluted	$ (4.81)	$ (1.83)	$ (2.02)
Weighted-average number of common shares used in computing net loss per share - basic and diluted	34,669	26,546	12,555
Other comprehensive income (loss):
Unrealized loss on available-for-sale securities, net of tax	$ (2,220)	$ (71)
Total other comprehensive loss	(2,220)	(71)
Comprehensive loss	$ (169,003)	$ (48,780)	$ (25,321)