Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operating expenses
General and administrative	$ (7,502)	$ (5,167)	$ (15,525)	$ (8,779)
Research and development	(10,627)	(6,676)	(22,245)	(12,046)
Loss from operations	(18,129)	(11,843)	(37,770)	(20,825)
Other income (expense), net	(505)	29	1,897	2,340
Net loss before income taxes	(18,634)	(11,814)	(35,873)	(18,485)
Income tax expense	(152)	0	(152)	0
Net loss	(18,786)	(11,814)	(36,025)	(18,485)
Net loss attributable to common stockholders—basic and diluted	$ (18,786)	$ (11,814)	$ (36,025)	$ (18,485)
Net loss per share attributable to common stockholders—basic and diluted (in USD per share)	$ (0.73)	$ (0.49)	$ (1.43)	$ (0.78)
Weighted average number of common shares outstanding—basic and diluted	25,841,530	23,893,651	25,225,521	23,806,009
Unrealized gain (loss) on available-for-sale investments	$ 17	$ 8	$ 66	$ (13)
Comprehensive loss	$ (18,769)	$ (11,806)	$ (35,959)	$ (18,498)