Description of Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands			6 Months Ended
	Jun. 14, 2019 USD ($) $ / shares shares	Jun. 13, 2019 shares	Jul. 31, 2019 USD ($)	Jan. 31, 2019 USD ($)
Description of Business and Basis of Presentation
Accumulated deficit			$ 573,574	$ 519,126
Net proceeds from issuance of common stock from IPO after deducting underwriters' discounts and commissions and estimated offering expenses			$ 665,092
Class A common stock | IPO
Description of Business and Basis of Presentation
Number of shares issued | shares	20,700,000
Public offering price | $ / shares	$ 34.00
Net proceeds from issuance of common stock from IPO after deducting underwriters' discounts and commissions and estimated offering expenses	$ 659,200
Underwriters' discounts and commissions and estimated offering expenses	$ 44,800
Stock Conversion, Common Stock Conversion Ratio	1
Class B common stock | IPO
Description of Business and Basis of Presentation
Number of shares issued in conversion of common stock | shares		131,267,586
Stock Conversion, Preferred Stock Conversion Ratio		1
Stock Conversion, Common Stock Conversion Ratio	1
Conversion Of Warrants, Warrants Issued | shares	336,386
Stock Conversion, Warrants Conversion Ratio	1