Condensed Statements of Convertible Preferred Stock shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) shares
Convertible Preferred Stock Rollforward
Issuance of common stock upon IPO, net of underwriters' discount and other offering costs of $2,902	$ 106,505
Common stock
Convertible Preferred Stock Rollforward
Issuance of common stock upon IPO, net of underwriters' discount and other offering costs of $2,902	$ 74
Issuance of common stock upon IPO, net of underwriters' discount and other offering costs of $2,902 (in shares) | shares	7,360
Additional paid-in capital
Convertible Preferred Stock Rollforward
Issuance of common stock upon IPO, net of underwriters' discount and other offering costs of $2,902	$ 106,431
Series A-1
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 22,650
Convertible preferred stock shares beginning balance | shares	151,773
Conversion of preferred stock upon IPO	$ (22,650)
Conversion of preferred stock upon IPO (in shares) | shares	(151,773)
Series A-2
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 39,979
Convertible preferred stock shares beginning balance | shares	173,453
Conversion of preferred stock upon IPO	$ (39,979)
Conversion of preferred stock upon IPO (in shares) | shares	(173,453)
Series B
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 69,757
Convertible preferred stock shares beginning balance | shares	234,955
Conversion of preferred stock upon IPO	$ (69,757)
Conversion of preferred stock upon IPO (in shares) | shares	(234,955)