Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating expenses:
Research and development	$ 12,991	$ 11,507	$ 24,238	$ 17,274
General and administrative	6,494	3,601	12,308	7,145
Total operating expenses	19,485	15,108	36,546	24,419
Loss from operations	(19,485)	(15,108)	(36,546)	(24,419)
Interest and other income, net	605	163	1,108	316
Loss before provision for income taxes	(18,880)	(14,945)	(35,438)	(24,103)
Provision for income taxes			3	2
Net loss	(18,880)	(14,945)	(35,441)	(24,105)
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale securities	142	(48)	711	34
Comprehensive loss	$ (18,738)	$ (14,993)	$ (34,730)	$ (24,071)
Net loss per common share:
Basic and diluted net loss per common share	$ (0.66)	$ (0.62)	$ (1.24)	$ (1.04)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share	28,665	24,224	28,603	23,079