Summary of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (1,876,160)	$ (1,750,699)
Net other comprehensive loss (income)	(76)	(69)
Ending Balance	(1,866,245)	(1,760,434)
Gain on Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(3,614)	(4,501)
Amounts reclassified from accumulated other comprehensive loss	221	219
Net other comprehensive loss (income)	221	219
Ending Balance	(3,393)	(4,282)
Defined Benefit Pension Plan [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	14,897	15,050
Amounts reclassified from accumulated other comprehensive loss	(297)	(288)
Net other comprehensive loss (income)	(297)	(288)
Ending Balance	14,600	14,762
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	11,283	10,549
Amounts reclassified from accumulated other comprehensive loss	(76)	(69)
Net other comprehensive loss (income)	(76)	(69)
Ending Balance	$ 11,207	$ 10,480