CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Expenses
Research and development	$ 68,487	$ 48,959	$ 26,071
General and administrative	15,292	15,755	12,699
Restructuring costs	0	0	334
Total operating expenses	83,779	64,714	39,104
Loss from operations	(83,779)	(64,714)	(39,104)
Other income (expense), net	661	170	(77)
Change in fair value of warrant liability	0	0	(4,517)
Loss before income taxes	(83,118)	(64,544)	(43,698)
Income tax benefit	0	0	0
Net loss	(83,118)	(64,544)	(43,698)
Unrealized gain (loss) on available-for-sale investments	25	(37)	(14)
Comprehensive loss	$ (83,143)	$ (64,507)	$ (43,684)
Loss per share, basic (in US$ per share)	$ (4.20)	$ (3.82)
Basic and diluted net loss per share (in dollars per share)			$ (3.24)
Weighted average number of shares used in computing net loss per share, basic and diluted (in shares)	19,787,349	16,901,826	13,483,467