Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Provision for Income Taxes	$ 25,541	$ 22,459	$ 30,479	$ 40,751
Effective Income Tax Rate Reconciliation, Percent	24.00%	46.00%	14.00%	25.00%
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Percent	13.00%		12.00%
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount			$ 22,222	$ 23,172
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent			10.00%	14.00%
Increase (Decrease) In Deferred Tax Assets Associated With Changes In Unrealized Gain Loss On Marketable Securities In Accumulated Other Comprehensive Income Loss			$ 130	$ (205)
Increase (Decrease) In Deferred Tax Assets Associated With Changes In Foreign Currency Translation Adjustment Gain Loss In Accumulated Other Comprehensive Income Loss			$ 1,108	$ (629)