Convertible Preferred Stock - Summary of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Jan. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Aug. 31, 2017
Temporary Equity [Line Items]
Shares Authorized	0		421,450,000
Shares Issued and Outstanding			69,910,520
Carrying Value			$ 309,137		$ 292,525
Liquidation Preference	$ 0		$ 333,058
Series A-1 Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized			310,350,000
Shares Issued and Outstanding			67,611,100
Issuance Price per Share			$ 4.50	$ 4.50		$ 4.50
Carrying Value			$ 303,224
Liquidation Preference			$ 322,100
Series A-2 Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized			11,100,000
Shares Issued and Outstanding			2,299,420
Issuance Price per Share			$ 2.57
Carrying Value			$ 5,913
Liquidation Preference			$ 10,958
Series B
Temporary Equity [Line Items]
Shares Authorized			100,000,000
Issuance Price per Share	$ 18.00	$ 18.00