Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses
Research and development	$ 14,993	$ 12,842	$ 45,744	$ 37,915
General and administrative	6,061	4,447	16,326	17,924
Restructuring charges (Note 4)	0	75	655	1,900
Total operating expenses	21,054	17,364	62,725	57,739
Loss from operations	(21,054)	(17,364)	(62,725)	(57,739)
Other income (expense)
Interest income	1,473	1,484	4,775	4,093
Interest expense	(2)	(4)	(18)	(25)
Net loss	$ (19,583)	$ (15,884)	$ (57,968)	$ (53,671)
Basic and diluted net loss per share (Note 5)	$ (0.14)	$ (0.12)	$ (0.42)	$ (0.39)
Total comprehensive loss (Note 9)	$ (19,653)	$ (15,673)	$ (57,546)	$ (53,490)
Weighted average number of shares used in computing basic and diluted net loss per share	139,589	138,586	139,025	138,344