Organization and Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 01, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Subsidiary Or Equity Method Investee [Line Items]
Convertible preferred stock outstanding		93,039,737		92,790,094
Initial share reserve		114,004,082
Convertible Preferred Stock
Subsidiary Or Equity Method Investee [Line Items]
Convertible preferred stock outstanding		93,039,737	93,023,694	92,790,094	92,790,094	92,745,734	92,656,029
Initial share reserve		93,039,737
Subsequent Event | 2019 Plan
Subsidiary Or Equity Method Investee [Line Items]
Initial share reserve	15,519,170
Initial Public Offering | Subsequent Event
Subsidiary Or Equity Method Investee [Line Items]
Shares issued	17,250,000
Public offering price	$ 20.00
Net proceeds	$ 316.0
Underwriting discounts, commissions and other costs	24.2
Offering expenses	$ 4.8