Redeemable Convertible Preferred Stock and Stockholders' Equity/(Deficit) - Summary of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Temporary Equity And Stockholder's Equity [Abstract]
Redeemable convertible preferred stock outstanding (in shares)	0	55,422,002	55,422,002	55,422,002
Stock options issued and outstanding (in shares)	13,180,950	13,291,684
Restricted stock units outstanding (in shares)	981,276	0
Shares available for future equity grants (in shares)	7,026,071	4,941,504
Total common stock reserved (in shares)	21,188,297	73,655,190