Equity Award Plans - Options to Purchase Series A Preferred Stock - Activity (Details) - Series A convertible preferred stock - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)	4,689,576
Granted (in shares)	195,312
Exercised (in shares)	(360,385)
Forfeited (in shares)	(351,562)
Converted to common stock options upon IPO (in shares)	(4,172,941)
Ending balance (in shares)	0	4,689,576
Weighted-Average Exercise Price
Beginning balance (in dollars per share)	$ 0.98
Granted (in dollars per share)	3.60
Exercised (in dollars per share)	0.59
Forfeited (in dollars per share)	0.52
Converted to common stock options upon IPO (in dollars per share)	1.18
Ending balance (in dollars per share)	$ 0.00	$ 0.98
Vested and expected to vest
Weighted-Average Remaining Contractual Term - Vested and expected to vest (in years)		5 years 2 months 5 days
Additional disclosures
Aggregate Intrinsic Value - Options, balance		$ 10,539