Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating expenses
General and administrative	$ (10,627)	$ (7,462)	$ (29,814)	$ (22,987)
Research and development	(12,688)	(9,904)	(38,301)	(32,149)
Loss from operations	(23,315)	(17,366)	(68,115)	(55,136)
Other income (expense), net	(460)	(523)	(1,490)	1,374
Net loss before income taxes	(23,775)	(17,889)	(69,605)	(53,762)
Income tax expense	(39)	(72)	(132)	(224)
Net loss	(23,814)	(17,961)	(69,737)	(53,986)
Net loss attributable to common stockholders—basic and diluted	$ (23,814)	$ (17,961)	$ (69,737)	$ (53,986)
Net loss per share attributable to common stockholders—basic and diluted (in USD per share)	$ (0.81)	$ (0.69)	$ (2.52)	$ (2.12)
Weighted average number of common shares outstanding—basic and diluted (shares)	29,380,453	26,061,993	27,632,090	25,507,409
Net loss	$ (23,814)	$ (17,961)	$ (69,737)	$ (53,986)
Unrealized gain (loss) on available-for-sale investments	(3)	9	166	75
Comprehensive loss	$ (23,817)	$ (17,952)	$ (69,571)	$ (53,911)