Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 445	$ 350	$ 545	$ 688
Operating expenses:
Research and development	12,909	9,703	25,586	20,087
General and administrative	3,473	3,742	7,294	7,393
Total operating expenses	16,382	13,445	32,880	27,480
Loss from operations	(15,937)	(13,095)	(32,335)	(26,792)
Other income (expense):
Interest and investment income	406	759	980	1,516
Interest expense	(2)	(5)	(5)	(12)
Other income (expense)	(2)	(3)	(3)	(2)
Other income (expense), net	402	751	972	1,502
Net loss	$ (15,535)	$ (12,344)	$ (31,363)	$ (25,290)
Net loss per share - basic and diluted	$ (0.44)	$ (0.45)	$ (0.91)	$ (0.96)
Weighted-average common stock outstanding - basic and diluted	34,967,761	27,242,514	34,604,738	26,284,262
Comprehensive loss:
Net loss	$ (15,535)	$ (12,344)	$ (31,363)	$ (25,290)
Net unrealized gain (loss) on marketable securities	159	29	104	133
Comprehensive loss	$ (15,376)	$ (12,315)	$ (31,259)	$ (25,157)