Summary of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ (1,716,896)	$ (1,545,010)
Net other comprehensive income	$ (574)	$ (2,382)	(1,834)	4,607
Ending Balance	(1,785,359)	(1,694,511)	(1,785,359)	(1,694,511)
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			(678)	(295)
Amounts reclassified from accumulated other comprehensive loss
Net other comprehensive income			(678)	(295)
Ending Balance	(1,642)	(852)	(1,642)	(852)
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			29	7,099
Amounts reclassified from accumulated other comprehensive loss			(74)	(1,193)
Net other comprehensive income			(45)	5,906
Ending Balance	(6,448)	(2,254)	(6,448)	(2,254)
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			(1,111)	(1,004)
Net other comprehensive income			(1,111)	(1,004)
Ending Balance	15,417	15,357	15,417	15,357
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			(649)	6,804
Amounts reclassified from accumulated other comprehensive loss			(1,185)	(2,197)
Net other comprehensive income			(1,834)	4,607
Ending Balance	$ 7,327	$ 12,251	$ 7,327	$ 12,251