Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Product revenue	$ 15,817	$ 23,339	$ 20,692	$ 14,800	$ 17,810	$ 8,666	$ 19,305	$ 2,722	$ 74,648	$ 48,503	$ 19,963
Research and development revenue	18,378	5,805	5,738	5,050	4,583	5,129	25,595	5,840
Total collaboration revenue	34,195	29,144	26,430	19,850	22,393	13,795	44,900	8,562	109,619	89,650	52,250
Net loss	41,539	(17,544)	(20,986)	(24,012)	(29,164)	(30,050)	(2,222)	(21,877)	(21,003)	(83,313)	(98,600)
Comprehensive loss	$ 41,375	$ (17,580)	$ (20,837)	$ (23,879)	$ (29,176)	$ (30,054)	$ (2,204)	$ (21,859)	$ (20,921)	$ (83,293)	$ (98,641)
Basic and diluted net loss per common share (in dollars per share)					$ (0.43)	$ (0.44)	$ (0.04)	$ (0.40)	$ (0.31)	$ (1.32)	$ (1.91)
Weighted average shares used in computing basic and diluted net loss per share (in shares)					68,138	68,004	61,680	54,492	68,656	63,130	51,664
Net (loss) income per share:
Basic (in dollars per shares)	$ 0.60	$ (0.26)	$ (0.31)	$ (0.35)
Diluted (in dollars per shares)	$ 0.60	$ (0.26)	$ (0.31)	$ (0.35)
Shares used in calculating net (loss) income per share:
Basic (in shares)	69,003	68,799	68,532	68,285
Diluted (in shares)	69,362	68,799	68,532	68,285