Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Provision for Income Taxes	$ 4,938	$ 18,292
Effective Income Tax Rate Reconciliation, Percent	4.00%	16.00%
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Percent	12.00%
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ 21,864	$ 22,957
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent	19.00%	20.00%
Increase (Decrease) In Deferred Tax Assets Associated With Changes In Unrealized Gain Loss On Marketable Securities In Accumulated Other Comprehensive Income Loss	$ 166	$ 21
Increase (Decrease) In Deferred Tax Assets Associated With Changes In Foreign Currency Translation Adjustment Gain Loss In Accumulated Other Comprehensive Income Loss	$ (1,095)	$ (140)