Employee Stock and Benefit Plans (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Outstanding Shares
Beginning balance (in shares)	4,495,891	7,527,680	7,579,058
Granted (in shares)	366,786	408,225	2,120,633
Exercised (in shares)	(1,183,235)	(2,997,095)	(1,399,157)
Canceled (in shares)	(250,133)	(442,919)	(772,854)
Ending balance (in shares)	3,429,309	4,495,891	7,527,680	7,579,058
Vested and Expected to vest (in shares)	3,230,498
Exercisable (in shares)	2,459,936
Weighted Average Exercise Price
Weighted average exercise price, beginning balance (in dollars per share)	$ 25.29	$ 19.25	$ 16.88
Weighted average exercise price, granted (in dollars per share)	79.79	40.82	26.64
Weighted average exercise price, exercised (in dollars per share)	20.33	11.05	10.83
Weighted average exercise price, canceled (in dollars per share)	39.61	33.29	31.57
Weighted average exercise price, ending balance (in dollars per share)	31.79	$ 25.29	$ 19.25	$ 16.88
Vested and Expected to vest, weighted average exercise price (in dollars per share)	30.27
Exercisable, Weighted average exercise price (in dollars per share)	$ 25.27
Weighted Average Remaining Contractual Life (Years)
Weighted average remaining contractual life	6 years 4 months 10 days	6 years 7 months 6 days	6 years	5 years 10 months 24 days
Vested and Expected to vest, weighted average remaining contractual life	6 years 2 months 2 days
Exercisable, weighted average remaining contractual life	5 years 7 months 25 days
Aggregate Intrinsic Value
Aggregate intrinsic value	$ 149,935	$ 153,129	$ 101,717	$ 131,345
Vested and Expected to vest, aggregate intrinsic value	145,521
Exercisable, aggregate intrinsic value	$ 121,696