Convertible Preferred Stock - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Mar. 21, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding	0		30,459,574
Dividends declared	$ 0
Common stock voting rights	one vote for each share
Common Stock | IPO
Temporary Equity [Line Items]
Convertible preferred stock converted into common stock		30,459,574
Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding	0		30,459,574	21,307,643	12,556,791
Series A Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding			12,556,791
Dividends declared per share rate	$ 0.24
Stated liquidation preference per share	3.96
Series B Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding			8,750,852
Dividends declared per share rate	0.48
Stated liquidation preference per share	8.00
Series C Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding			9,151,931
Dividends declared per share rate	0.71
Stated liquidation preference per share	$ 11.6915