Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	10,000,000		0
Preferred stock, shares issued	0		0
Preferred stock, shares outstanding	0		0
Common stock, par value	$ 0.0001		$ 0.0001
Common stock, shares authorized	300,000,000		181,000,000
Common stock, shares issued	35,465,715		1,846,024
Common stock, shares outstanding	35,465,715		1,846,024
Series A Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	0		56,000,000
Preferred stock, shares issued	0		56,000,000
Preferred stock, shares outstanding	0	56,000,000	56,000,000	56,000,000	56,000,000	56,000,000	56,000,000
Preferred stock. aggregate liquidation preference	$ 0		$ 62,468
Series B Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	0		49,501,221
Preferred stock, shares issued	0		49,501,221
Preferred stock, shares outstanding	0	49,501,221	49,501,221	49,501,221	49,501,221	49,501,221	49,501,221
Preferred stock. aggregate liquidation preference	$ 0		$ 75,860
Series C Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares authorized	0		44,000,000
Preferred stock, shares issued	0		26,360,745
Preferred stock, shares outstanding	0	54,888,058	26,360,745
Preferred stock. aggregate liquidation preference	$ 0		$ 47,947