Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating expenses
Research and development	$ 15,400	$ 10,515	$ 44,440	$ 21,006
General and administrative	5,124	3,577	17,861	9,167
Total operating expenses	20,524	14,092	62,301	30,173
Loss from operations	(20,524)	(14,092)	(62,301)	(30,173)
Interest income	54	50	168	89
Other income (expense), net	91	208	81	(11,776)
Net loss and comprehensive loss	(20,379)	(13,834)	(62,052)	(41,860)
Deemed dividend related to beneficial conversion feature of convertible preferred stock				(25,559)
Net loss attributable to common stockholders	$ (20,379)	$ (13,834)	$ (62,052)	$ (67,419)
Net loss per basic and diluted share attributable to common stockholders	$ (0.69)	$ (0.57)	$ (2.15)	$ (3.93)
Weighted-average common shares used to compute basic and diluted net loss per share	29,354	24,195	28,825	17,138