Equity Award Plans - Options to Purchase Common Stock - Activity (Details) - Common Stock - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended	12 Months Ended
	May 08, 2018	Jun. 30, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)		14,183,221
Granted (in shares)		2,905,375
Exercised (in shares)		(624,019)
Forfeited (in shares)		(543,216)
Series A options converted to common stock options upon IPO (in shares)		1,693,197
Series E-1 options converted to common stock options upon IPO (in shares)	837,835	837,835
Ending balance (in shares)		18,452,393	14,183,221
Weighted-Average Exercise Price
Beginning balance (in dollars per share)		$ 4.89
Granted (in dollars per share)		12.28
Exercised (in dollars per share)		4.04
Forfeited (in dollars per share)		6.18
Series A options converted to common stock options upon IPO (in dollars per share)		2.90
Series E-1 options converted to common stock options upon IPO (in dollars per share)		0.86
Ending balance (in dollars per share)		$ 5.68	$ 4.89
Vested and expected to vest
Number of Shares - Vested and expected to vest (in shares)		17,748,554
Weighted-Average Exercise Price - Vested and expected to vest (in dollars per share)		$ 5.54
Weighted-Average Remaining Contractual Term - Vested and expected to vest (in years)		6 years 11 months 12 days
Aggregate Intrinsic Value - Vested and expected to vest		$ 363,193
Additional disclosures
Weighted-Average Remaining Contractual Term - Options, balance (in years)		7 years 11 days	7 years 1 month 28 days
Aggregate Intrinsic Value - Options, balance		$ 375,031	$ 17,626
Number of Shares - Options vested and exercisable (in shares)		10,612,656
Weighted-Average Exercise Price - Options vested and exercisable (in dollars per share)		$ 3.81
Weighted-Average Remaining Contractual Term - Options vested and exercisable (in years)		5 years 8 months 16 days
Aggregate Intrinsic Value - Options vested and exercisable		$ 235,524