Summary of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (1,716,896)	$ (1,545,010)
Net other comprehensive (income) loss	(1,203)	3,665
Ending Balance	(1,746,863)	(1,622,590)
Gain on Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(964)	(557)
Change excluding amounts reclassified from accumulated other comprehensive loss	(298)	(18)
Amounts reclassified from accumulated other comprehensive loss
Net other comprehensive (income) loss	(298)	(18)
Ending Balance	(1,262)	(575)
Gain on Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(6,403)	(8,160)
Change excluding amounts reclassified from accumulated other comprehensive loss	(389)	4,431
Amounts reclassified from accumulated other comprehensive loss	(139)	(371)
Net other comprehensive (income) loss	(528)	4,060
Ending Balance	(6,931)	(4,100)
Defined Benefit Pension Plan [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	16,528	16,361
Amounts reclassified from accumulated other comprehensive loss	(377)	(377)
Net other comprehensive (income) loss	(377)	(377)
Ending Balance	16,151	15,984
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	9,161	7,644
Change excluding amounts reclassified from accumulated other comprehensive loss	(687)	4,413
Amounts reclassified from accumulated other comprehensive loss	(516)	(748)
Net other comprehensive (income) loss	(1,203)	3,665
Ending Balance	$ 7,958	$ 11,309