Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 3,528	$ 7,340	$ 8,077	$ 13,359
General and administrative	4,058	6,971	9,282	12,929
Restructuring charges			3,994
Total operating expenses	7,586	14,311	21,353	26,288
Loss from operations	(7,586)	(14,311)	(21,353)	(26,288)
Other expense (income), net	301	138	480	78
Net loss	$ (7,887)	$ (14,449)	$ (21,833)	$ (26,366)
Net loss per share, basic and diluted	$ (0.20)	$ (0.40)	$ (0.54)	$ (0.73)
Weighted average number of shares of common stock used in computing net loss per share, basic and diluted	40,129,304	36,278,567	40,101,789	36,098,171
Comprehensive loss:
Net loss	$ (7,887)	$ (14,449)	$ (21,833)	$ (26,366)
Other comprehensive income (loss):
Change in unrealized gain (loss) on available-for-sale securities	(52)	23	(5)	24
Comprehensive loss	$ (7,939)	$ (14,426)	$ (21,838)	$ (26,342)