Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenue:
Collaboration revenue	$ 1,552	$ 4,940	$ 3,051	$ 11,284
Total revenue	1,552	4,940	3,051	11,284
Operating expenses:
Research and development	41,760	44,266	83,671	67,985
General and administrative	18,363	10,724	34,318	18,060
Change in fair value of contingent consideration	1,404	1,973	2,417	2,188
Total operating expenses	61,527	56,963	120,406	88,233
Loss from operations	(59,975)	(52,023)	(117,355)	(76,949)
Other income, net	905	228	1,866	367
Loss before income taxes	(59,070)	(51,795)	(115,489)	(76,582)
Income tax benefit	226		371
Net loss	$ (58,844)	$ (51,795)	$ (115,118)	$ (76,582)
Net loss per share - basic and diluted:	$ (1.59)	$ (1.57)	$ (3.12)	$ (2.34)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	36,954	32,955	36,937	32,757
Other comprehensive income (loss):
Unrealized gain on available-for-sale securities, net of tax of $0.2 and $0.9 million for the three and six months ended June 30, 2016, respectively	$ 330	$ 70	$ 1,649	$ 18
Comprehensive loss	$ (58,514)	$ (51,725)	$ (113,469)	$ (76,564)