Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating expenses
General and administrative	$ (7,462)	$ (4,944)	$ (22,987)	$ (13,723)
Research and development	(9,904)	(8,230)	(32,149)	(20,276)
Loss from operations	(17,366)	(13,174)	(55,136)	(33,999)
Other income (expense), net	(523)	27	1,374	2,367
Net loss before income taxes	(17,889)	(13,147)	(53,762)	(31,632)
Income tax expense	(72)	0	(224)	0
Net loss	(17,961)	(13,147)	(53,986)	(31,632)
Net loss attributable to common stockholders—basic and diluted	$ (17,961)	$ (13,147)	$ (53,986)	$ (31,632)
Net loss per share attributable to common stockholders—basic and diluted (in USD per share)	$ (0.69)	$ (0.54)	$ (2.12)	$ (1.32)
Weighted average number of common shares outstanding—basic and diluted	26,061,993	24,325,166	25,507,409	23,980,963
Unrealized gain (loss) on available-for-sale investments	$ 9	$ 4	$ 75	$ (9)
Comprehensive loss	$ (17,952)	$ (13,143)	$ (53,911)	$ (31,641)