CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Expenses
Research and development	$ 11,276	$ 7,149	$ 19,483	$ 12,109
General and administrative	4,240	2,986	8,019	5,671
Restructuring costs	0	0	0	334
Total operating expenses	15,516	10,135	27,502	18,114
Loss from operations	(15,516)	(10,135)	(27,502)	(18,114)
Other income (expense), net	70	73	116	(129)
Change in fair value of warrant liability	0	(976)	0	(6,451)
Net loss	(15,446)	(11,038)	(27,386)	(24,694)
Unrealized gain (loss) on available-for-sale investments	(9)	24	(4)	34
Comprehensive loss	$ (15,455)	$ (11,014)	$ (27,390)	$ (24,660)
Basic and diluted net loss per share	$ (0.95)	$ (0.82)	$ (1.74)	$ (1.83)
Weighted average number of shares used in computing net loss per share, basic and diluted	16,235,261	13,498,828	15,727,891	13,467,420