Redeemable Convertible Preferred Stock - Summary of Preferred Stock (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Jul. 31, 2016	Jan. 31, 2016
Temporary Equity [Line Items]
Preferred Shares Authorized	63,491,857	34,972,535			22,380,952
Preferred Shares Issued		34,783,832
Preferred Shares Outstanding		34,783,832
Carrying Value		$ 26,500,000
Liquidation Preference		$ 26,500,000
Common Stock Issuable Upon Conversion		8,418,149
Series Seed Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	3,333,333	3,333,333			3,333,333
Preferred Shares Issued		3,333,333					3,333,333
Preferred Shares Outstanding		3,333,333
Carrying Value		$ 1,500,000
Liquidation Preference		$ 1,500,000
Common Stock Issuable Upon Conversion		806,711
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	31,639,202	31,639,202			19,047,619
Preferred Shares Issued		31,450,499	17,612,279	4,403,070		5,714,286
Preferred Shares Outstanding		31,450,499
Carrying Value		$ 25,000,000
Liquidation Preference		$ 25,000,000
Common Stock Issuable Upon Conversion		7,611,438