Stock-based Compensation - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Outstanding Shares
Beginning balance (in shares)	4,495,891
Granted (in shares)	61,850
Exercised (in shares)	(286,597)
Canceled (in shares)	(83,608)
Ending balance (in shares)	4,187,536
Vested and expected to vest (in shares)	3,969,350
Exercisable (in shares)	2,895,704
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)	59.95
Weighted average exercise price, exercised (in dollars per share)	27.68
Weighted average exercise price, canceled (in dollars per share)	38.62
Weighted average exercise price, Ending balance (in dollars per share)	25.37
Weighted average exercise price, Vested and expected to vest (in dollars per share)	24.76
Weighted average exercise price, Exercisable (in dollars per share)	$ 21.89
Weighted Average Remaining Contractual Life
Weighted average remaining contractual life (in years)	6 years 5 months 27 days	6 years 7 months 6 days
Weighted Average Remaining Contractual Life (Years), Vested and Expected to Vest	6 years 4 months 17 days
Weighted Average Remaining Contractual Life (Years), Exercisable	5 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate intrinsic value	$ 198,395,610		$ 153,129
Aggregate intrinsic value, Vested and expected to vest	190,509,569
Aggregate intrinsic value, Exercisable	$ 147,268,457