Stock-based Compensation - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Outstanding Shares
Beginning balance (in shares)	4,495,891
Granted (in shares)	154,025
Exercised (in shares)	(430,848)
Canceled (in shares)	(164,766)
Ending balance (in shares)	4,054,302
Vested and expected to vest (in shares)	3,863,453
Exercisable (in shares)	2,921,338
Weighted Average Exercise Price
Weighted average exercise price, Beginning balance (in dollars per share)	$ 25.29
Weighted average exercise price, granted (in dollars per share)	71.26
Weighted average exercise price, exercised (in dollars per share)	28.25
Weighted average exercise price, canceled (in dollars per share)	38.38
Weighted average exercise price, Ending balance (in dollars per share)	26.19
Weighted average exercise price, Vested and expected to vest (in dollars per share)	25.32
Weighted average exercise price, Exercisable (in dollars per share)	$ 22.06
Weighted Average Remaining Contractual Life
Weighted average remaining contractual life (in years)	6 years 3 months 7 days	6 years 7 months 6 days
Weighted Average Remaining Contractual Life (Years), Vested and Expected to Vest	6 years 1 month 28 days
Weighted Average Remaining Contractual Life (Years), Exercisable	5 years 6 months 11 days
Aggregate Intrinsic Value
Aggregate intrinsic value	$ 235,597		$ 153,129
Aggregate intrinsic value, Vested and expected to vest	227,859
Aggregate intrinsic value, Exercisable	$ 181,818