Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Stock option activity
Outstanding	3,037,690
Granted	792,920
Exercised	(183,987)
Cancelled	(54,390)
Outstanding	3,592,233	3,037,690
Exercisable at end of period	1,086,727
Vested and expected to vest at end of period	3,335,355
Weighted average exercise price per share
Outstanding	$ 13.00
Granted	24.23
Exercised	12.90
Cancelled	15.27
Outstanding	15.45	$ 13.00
Exercisable at end of period	13.17
Vested and expected to vest at end of period	$ 15.09
Stock option activity, additional information
Outstanding Weighted-Average Remaining Contractual Term	8 years 7 months 6 days	8 years 4 months 24 days
Outstanding Aggregate Intrinsic Value	$ 36,741	$ 16,829
Exercisable at end of period, Weighted-Average Remaining Contractual Term	7 years 7 months 6 days
Exercisable at end of period, Aggregate Intrinsic Value	$ 13,453
Vested and expected to vest at end of period, Weighted-Average Remaining Contractual Term	8 years 6 months
Vested and expected to vest at end of period, Aggregate Intrinsic Value	$ 35,236