Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Collaboration revenue	$ 8,068	$ 6,160	$ 19,798	$ 20,081
Operating expenses:
Research and development	39,300	18,150	101,058	57,058
General and administrative	7,378	4,893	19,894	14,227
Total operating expenses	46,678	23,043	120,952	71,285
Other income (expense):
Other income, net	954	158	2,240	350
Interest expense	(47)	(109)	(178)	(378)
Total other income (expense)	907	49	2,062	(28)
Net loss	(37,703)	(16,834)	(99,092)	(51,232)
Other comprehensive loss:
Unrealized gain (loss) on investments	$ 89	$ (28)	$ (147)	$ 27
Net loss per share applicable to common stockholders - basic and diluted	$ (0.96)	$ (0.62)	$ (2.67)	$ (1.89)
Comprehensive loss	$ (37,614)	$ (16,862)	$ (99,239)	$ (51,205)
Weighted-average number of common shares used in net loss per share applicable to common stockholders - basic and diluted	39,130	27,251	37,053	27,170