Stockholders' Equity (Stock Option Plan Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Shares
Balance as of December 31, 2014	1,800,697
Granted	262,747
Exercised	(212,349)
Forfeited	(78,685)
Balance as of June 30, 2015	1,772,410	1,800,697
Exercisable as of June 30, 2015	1,139,894
Options vested and expected to vest as of June 30, 2015	1,772,410
Weighted Average Exercise Price (in USD per share)
Balance as of December 31, 2014	$ 28.78
Granted	58.84
Exercised	25.58
Forfeited	45.75
Balance as of June 30, 2015	32.86	$ 28.78
Exercisable as of June 30, 2015	23.62
Options vested and expected to vest as of June 30, 2015	$ 32.86
Weighted-Average Remaining Contractual Term in Years
Weighted average remaining contractual term in years	6 years 11 months 27 days	7 years 3 months
Exercisable	6 years 1 month 10 days
Options vested and expected to vest	6 years 11 months 27 days
Aggregate Intrinsic Value
Aggregate intrinsic value	$ 120,588	$ 51,558
Exercisable	88,090
Options vested and expected to vest	$ 120,588