Redeemable Convertible Preferred Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2018	Dec. 31, 2017	Jul. 26, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options issued and outstanding (in shares)	11,821,024	13,180,950
2017 Equity Incentive Plan:
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options issued and outstanding (in shares)	11,821,024	13,180,950
Restricted stock units outstanding (in shares)	1,152,718	981,276
Shares available for future equity grants (in shares)	7,011,507	7,026,071
Total common stock reserved (in shares)	19,985,249	21,188,297	7,895,659
2017 Employee Stock Purchase Plan:
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved (in shares)	2,414,688	1,600,000