Summary Of Significant Accounting Policies (Summary Of The Most Significant Impacts Of The New Accounting Guidance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase in operating activities	$ 373,276	$ 338,943	$ 221,802
Decrease in financing activities	208,016	222,196	100,990
Accounting Standards Update 2016-09 [Member]
Effective Income Tax Rate Reconciliation, Deduction, Amount	$ 27,700
Weighted Average Number Diluted Shares Outstanding Adjustment	450,000
Accounting Standards Update 2016-09 [Member] | Tax Benefits Related To Share-based Payments At Settlement Classified As Operating Cash Flows Instead Of Financing Cash Flows [Member]
Increase in operating activities	$ 27,700
Decrease in financing activities	27,700
Accounting Standards Update 2016-09 [Member] | Cash Payments To Tax Authorities For Shares Withheld To Meet Tax Withholding Requirements On Restricted Stock Units Are Classified As Financing Cash Flow Instead Of Operating Cash Flow [Member]
Increase in operating activities	8,100	4,400	5,400
Decrease in financing activities	$ 8,100	$ 4,400	$ 5,400