Property And Equipment, Net (Summary Of Depreciation And Amortization, Capitalized Computer Software For Internal Use And Unpaid Property Equipment Reflected In Account Payable And Accrued Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 73,797	$ 63,537	$ 57,029
Unpaid property and equipment, reflected in accounts payable and accrued liabilities	11,744	10,601	8,534
Software Developed For Internal Use [Member]
Property, Plant and Equipment [Line Items]
Capitalized computer software developed for internal use	$ 16,131	$ 15,590	$ 19,081