Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Collaboration revenue	$ 6,155	$ 14,079	$ 25,031
Research and license fees			390
Total revenue	6,155	14,079	25,421
Operating expenses:
Research and development	204,775	134,038	62,574
General and administrative	65,119	46,209	23,227
Change in fair value of contingent consideration	4,091	2,869	246
Total operating expenses	273,985	183,116	86,047
Loss from operations	(267,830)	(169,037)	(60,626)
Other income, net	3,711	2,314	120
Loss before income taxes	(264,119)	(166,723)	(60,506)
Income tax benefit (expense)	612	(60)	11,797
Net loss	$ (263,507)	$ (166,783)	$ (48,709)
Net loss per share - basic and diluted	$ (7.07)	$ (4.81)	$ (1.83)
Weighted-average number of common shares used in computing net loss per share - basic and diluted	37,284	34,669	26,546
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net of tax expense of $0.6 and $0.0 million for the years ended December 31, 2016 and 2015, respectively	$ 1,142	$ (2,220)	$ (71)
Total other comprehensive income (loss)	1,142	(2,220)	(71)
Comprehensive loss	$ (262,365)	$ (169,003)	$ (48,780)