Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue:
Collaboration revenue	$ 6,832	$ 1,499
Total revenue	6,832	1,499
Operating expenses:
Research and development	55,028	41,911
General and administrative	20,284	15,955
Change in fair value of contingent consideration	1,433	1,013
Total operating expenses	76,745	58,879
Loss from operations	(69,913)	(57,380)
Other income, net	1,201	961
Loss before income taxes	(68,712)	(56,419)
Income tax benefit		145
Net loss	$ (68,712)	$ (56,274)
Net loss per share - basic and diluted:	$ (1.68)	$ (1.52)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	40,836	36,920
Other comprehensive (loss) income:
Unrealized (loss) gain on available-for-sale securities, net of tax expense of $0.0 million and $0.7 million for the three months ended March 31, 2017 and 2016, respectively	$ (101)	$ 1,319
Comprehensive loss	$ (68,813)	$ (54,955)