Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues:
License revenue	$ 10,570		$ 10,570
Collaboration revenue	6,146	$ 1,552	12,978	$ 3,051
Total revenues	16,716	1,552	23,548	3,051
Operating expenses:
Research and development	64,311	41,760	119,339	83,671
General and administrative	21,197	18,363	41,481	34,318
Change in fair value of contingent consideration	(970)	1,404	463	2,417
Total operating expenses	84,538	61,527	161,283	120,406
Loss from operations	(67,822)	(59,975)	(137,735)	(117,355)
Interest (expense) income, net	(2,242)	981	(687)	1,932
Other (expense) income, net	(834)	(76)	(1,189)	(66)
Loss before income taxes	(70,898)	(59,070)	(139,611)	(115,489)
Income tax benefit		226		371
Net loss	$ (70,898)	$ (58,844)	$ (139,611)	$ (115,118)
Net loss per share - basic and diluted:	$ (1.73)	$ (1.59)	$ (3.41)	$ (3.12)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	41,035	36,954	40,936	36,937
Other comprehensive (loss) income:
Unrealized (loss) gain on available-for-sale securities, net of tax of $0.0 million for the three and six months ended June 30, 2017 and $0.2 and $0.9 million for the three and six months ended June 30, 2016, respectively	$ (165)	$ 330	$ (266)	$ 1,649
Comprehensive loss	$ (71,063)	$ (58,514)	$ (139,877)	$ (113,469)