Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues
Collaboration revenue	$ 5,840	$ 6,856
Operating expenses:
Research and development	28,487	17,635
General and administrative	5,683	4,646
Total operating expenses	34,170	22,281
Other income (expense):
Other income (expense), net	425	61
Interest expense	(72)	(140)
Total other income (expense)	353	(79)
Net loss	(27,977)	(15,504)
Other comprehensive loss:
Unrealized (loss) gain on investments	(114)	31
Comprehensive loss	$ (28,091)	$ (15,473)
Reconciliation of net loss applicable to common stockholders:
Net loss per share applicable to common stockholders - basic and diluted	$ (0.84)	$ (0.57)
Weighted-average number of common shares used in net loss per share applicable to common stockholders - basic and diluted	33,190	27,088