Convertible Preferred Stock - Summary of Outstanding Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2020	May 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Preferred Stock Authorized	57,932,090		33,645,447
Preferred Stock Issued	48,958,829		33,645,447
Preferred Stock Outstanding	48,958,829		33,645,447
Carrying Value	$ 175,745
Liquidation Preference	$ 178,106		$ 70,606
Common Stock Issuable Upon Conversion	48,958,829
Series A Preferred
Class Of Stock [Line Items]
Preferred Stock Authorized	20,000,000
Preferred Stock Issued	20,000,000
Preferred Stock Outstanding	20,000,000
Carrying Value	$ 19,136
Liquidation Preference	$ 20,000
Common Stock Issuable Upon Conversion	20,000,000
Series B Preferred
Class Of Stock [Line Items]
Preferred Stock Authorized	7,592,830
Preferred Stock Issued	7,592,830
Preferred Stock Outstanding	7,592,830
Carrying Value	$ 22,619
Liquidation Preference	$ 23,006
Common Stock Issuable Upon Conversion	7,592,830
Series C Preferred
Class Of Stock [Line Items]
Preferred Stock Authorized	6,052,617
Preferred Stock Issued	6,052,617
Preferred Stock Outstanding	6,052,617
Carrying Value	$ 27,359
Liquidation Preference	$ 27,600
Common Stock Issuable Upon Conversion	6,052,617
Series D Preferred
Class Of Stock [Line Items]
Preferred Stock Authorized	15,313,382	15,313,382
Preferred Stock Issued	15,313,382	15,313,382
Preferred Stock Outstanding	15,313,382
Carrying Value	$ 106,631
Liquidation Preference	$ 107,500
Common Stock Issuable Upon Conversion	15,313,382
Series D-1 Preferred
Class Of Stock [Line Items]
Preferred Stock Authorized	8,973,261	8,973,261