Stock-Based Compensation - Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of shares
Outstanding at beginning of period (in shares)	2,883,175
Granted (in shares)	384,500
Exercised (in shares)	(398,895)
Forfeited (in shares)	(59,139)
Outstanding at end of the period (in shares)	2,809,641
Options vested and expected to vest at end of the period (in shares)	2,809,641
Exercisable at end of period (in shares)	1,385,167
Weighted average exercise price
Outstanding at beginning of period (in dollars per share)	$ 9.26
Granted (in dollars per share)	29.32
Exercised (in dollars per share)	4.36
Forfeited (in dollars per share)	16.77
Outstanding at end of period (in dollars per share)	12.54
Options vested and expected to vest at end of period (in dollars per share)	12.54
Exercisable at end of period (in dollars per share)	$ 6.72
Weighted average remaining contractual term
Outstanding	7 years 7 months 6 days
Options vested and expected to vest at of the period	7 years 7 months 6 days
Exercisable	6 years 1 month 6 days
Aggregate intrinsic value
Outstanding (in dollars)	$ 73,778
Options vested and expected to vest at end of period (in dollars)	73,778
Exercisable (in dollars)	44,431
Additional disclosures
Intrinsic value of options exercised (in dollars)	12,055	$ 8,660
Proceeds from stock options exercised (in dollars)	$ 920	$ 50
Shares delivered as payment for exercise	23,991	329,587
Stock options exercised in cashless transaction	234,465	776,422
Gross cashless exercise value	$ 819	$ 2,816
Stock options
Additional disclosures
Total unrecognized compensation cost (in dollars)	$ 13,799
Weighted average period expected to be recognized	1 year 8 months 19 days