Common Stock, Redeemable Common Stock, and Convertible Preferred Stock (converted to Common Stock) - Convertible Preferred Stock (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) shares
Temporary Equity [Line Items]
Preferred Stock Designated (in shares)	49,413,523
Preferred Stock Issued (in shares)	40,079,567
Preferred Stock Outstanding (in shares)	40,079,567
Carrying Value | $	$ 64,675
Liquidation Preference | $	$ 84,067
Common Stock Issuable Upon Conversion	3,808,430
Series Seed preferred stock
Temporary Equity [Line Items]
Preferred Stock Designated (in shares)	2,313,523
Preferred Stock Issued (in shares)	1,516,136
Preferred Stock Outstanding (in shares)	1,516,136
Carrying Value | $	$ 1,310
Liquidation Preference | $	$ 1,444
Common Stock Issuable Upon Conversion	143,630
Series A preferred stock
Temporary Equity [Line Items]
Preferred Stock Designated (in shares)	22,000,000
Preferred Stock Issued (in shares)	19,946,862
Preferred Stock Outstanding (in shares)	19,946,862
Carrying Value | $	$ 32,480
Liquidation Preference | $	$ 47,624
Common Stock Issuable Upon Conversion	1,895,610
Series B preferred stock
Temporary Equity [Line Items]
Preferred Stock Designated (in shares)	25,100,000
Preferred Stock Issued (in shares)	18,616,569
Preferred Stock Outstanding (in shares)	18,616,569
Carrying Value | $	$ 30,885
Liquidation Preference | $	$ 34,999
Common Stock Issuable Upon Conversion	1,769,190