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
Operating expenses:
Research and development	$ 20,598	$ 18,802	$ 56,435	$ 43,040
General and administrative	11,062	7,140	29,295	19,448
Total operating expenses	31,660	25,942	85,730	62,488
Loss from operations	(31,660)	(25,942)	(85,730)	(62,488)
Interest and other income, net	564	576	1,554	1,684
Loss before provision for income taxes	(31,096)	(25,366)	(84,176)	(60,804)
Provision for income taxes	0	7	2	10
Net loss	(31,096)	(25,373)	(84,178)	(60,814)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale securities	26	(158)	95	553
Comprehensive loss	$ (31,070)	$ (25,531)	$ (84,083)	$ (60,261)
Net loss per common share:
Basic and diluted net loss per common share	$ (1.02)	$ (0.88)	$ (2.84)	$ (2.12)
Weighted-average shares outstanding used to calculate basic and diluted net loss per common share	30,474	28,801	29,597	28,670