CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expenses
Research and development	$ 58,085	$ 68,487	$ 48,959
General and administrative	13,450	15,292	15,755
Total operating expenses	71,535	83,779	64,714
Loss from operations	(71,535)	(83,779)	(64,714)
Other income, net	1,105	661	170
Net loss	(70,430)	(83,118)	(64,544)
Unrealized gain (loss) on available-for-sale investments	54	25	(37)
Comprehensive loss	$ (70,484)	$ (83,143)	$ (64,507)
Loss per share, basic (in US$ per share)	$ (2.78)	$ (4.20)	$ (3.82)
Weighted average number of shares used in computing net loss per share, basic and diluted (in shares)	25,290,222	19,787,349	16,901,826