Statements of Convertible Preferred Stock - USD ($) shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Series A-1
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 22,650	$ 22,650
Convertible preferred stock shares beginning balance	151,773	151,773
Conversion of preferred stock upon IPO	$ (22,650)
Conversion of preferred stock upon IPO (in shares)	(151,773)
Convertible preferred stock shares ending balance	0	151,773
Convertible preferred stock ending balance		$ 22,650
Series A-2
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 39,979
Convertible preferred stock shares beginning balance	173,453
Issuance of convertible preferred stock, net of issuance costs		$ 39,979
Issuance of convertible preferred stock, net of issuance costs (in shares)		173,453
Conversion of preferred stock upon IPO	$ (39,979)
Conversion of preferred stock upon IPO (in shares)	(173,453)
Convertible preferred stock shares ending balance	0	173,453
Convertible preferred stock ending balance		$ 39,979
Series B
Convertible Preferred Stock Rollforward
Convertible preferred stock beginning balance	$ 69,757
Convertible preferred stock shares beginning balance	234,955
Issuance of convertible preferred stock, net of issuance costs		$ 69,757
Issuance of convertible preferred stock, net of issuance costs (in shares)		234,955
Conversion of preferred stock upon IPO	$ (69,757)
Conversion of preferred stock upon IPO (in shares)	(234,955)
Convertible preferred stock shares ending balance	0	234,955
Convertible preferred stock ending balance		$ 69,757