Summary of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (1,809,842,000)	$ (1,716,896,000)
Cumulative effect adjustment of accounting standards (see Note 2)	1,541,000	0
Net other comprehensive loss (income)	1,983,000	(1,203,000)
Ending Balance	(1,906,343,000)	(1,746,863,000)
Gain on Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(1,541,000)	(964,000)
Cumulative effect adjustment of accounting standards (see Note 2)	1,541,000
Change excluding amounts reclassified from accumulated other comprehensive loss		(298,000)
Amounts reclassified from accumulated other comprehensive loss
Net other comprehensive loss (income)	0	(298,000)
Ending Balance	0	(1,262,000)
Gain on Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7,424,000)	(6,403,000)
Change excluding amounts reclassified from accumulated other comprehensive loss	(1,379,000)	(389,000)
Amounts reclassified from accumulated other comprehensive loss	3,633,000	(139,000)
Net other comprehensive loss (income)	2,254,000	(528,000)
Ending Balance	(5,170,000)	(6,931,000)
Defined Benefit Pension Plan [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	15,135,000	16,528,000
Amounts reclassified from accumulated other comprehensive loss	(271,000)	(377,000)
Net other comprehensive loss (income)	(271,000)	(377,000)
Ending Balance	14,864,000	16,151,000
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	6,170,000	9,161,000
Cumulative effect adjustment of accounting standards (see Note 2)	1,541,000
Change excluding amounts reclassified from accumulated other comprehensive loss	(1,379,000)	(687,000)
Amounts reclassified from accumulated other comprehensive loss	3,362,000	(516,000)
Net other comprehensive loss (income)	1,983,000	(1,203,000)
Ending Balance	$ 9,694,000	$ 7,958,000