Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue — related party	$ 4,814		$ 37,352
Operating expenses:
Research and development	(16,884)	$ (10,779)	(48,339)	$ (35,626)
General and administrative	(4,591)	(2,583)	(11,642)	(7,827)
Total operating expenses	(21,475)	(13,362)	(59,981)	(43,453)
Loss from operations	(16,661)	(13,362)	(22,629)	(43,453)
Interest income	72	148	392	701
Other income (expense), net	55	(41)	(269)	(48)
Net loss	(16,534)	(13,255)	(22,506)	(42,800)
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock		(1,375)		(4,078)
Net loss attributable to common stockholders	$ (16,534)	$ (14,630)	$ (22,506)	$ (46,878)
Net loss per share, attributable to common stockholders:
Basic	$ (0.47)	$ (8.53)	$ (1.36)	$ (30.03)
Diluted	$ (0.47)	$ (8.53)	$ (1.36)	$ (30.03)
Shares used in computing net loss per share attributable to common stockholders:
Basic	35,445,504	1,714,285	16,592,746	1,561,242
Diluted	35,445,504	1,714,285	16,592,746	1,561,242
Comprehensive loss:
Net loss	$ (16,534)	$ (13,255)	$ (22,506)	$ (42,800)
Net unrealized gain (loss) on short-term investments	12	(10)	(17)	1
Total other comprehensive income (loss)	12	(10)	(17)	1
Comprehensive loss	$ (16,522)	$ (13,265)	$ (22,523)	$ (42,799)