Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	Oct. 10, 2019	Jan. 31, 2019	Sep. 30, 2019	Oct. 11, 2019	Jun. 30, 2019	Dec. 31, 2018
Subsidiary Sale Of Stock [Line Items]
Net proceeds from sale of convertible preferred stock			$ 317,335
IPO
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock, shares outstanding	88,112,733			0
Series B Convertible Preferred Stock
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock, shares sold		18,202,213	18,202,213
Convertible preferred stock, shares sold, price per share		$ 18.00
Net proceeds from sale of convertible preferred stock		$ 327,500
Convertible preferred stock, additional shares authorized		4,020,009
Convertible Preferred Stock
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock, shares outstanding			88,112,733		88,112,733	69,910,520
Convertible Preferred Stock | IPO | Common Stock
Subsidiary Sale Of Stock [Line Items]
Number of convertible preferred stock converted to shares of common stock (in shares)	88,112,733