Summary Of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,750,699)	$ (1,809,842)	$ (1,716,896)
Cumulative effect adjustment of accounting standards	0	1,541	0
Net other comprehensive loss (income)	734	2,838	(2,991)
Ending balance	(1,876,160)	(1,750,699)	(1,809,842)
Gain on Investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	(1,541)	(964)
Change excluding amounts reclassified from accumulated other comprehensive loss	0	0	(1,228)
Amounts reclassified from accumulated other comprehensive loss	0	0	651
Cumulative effect adjustment of accounting standards		1,541
Net other comprehensive loss (income)	0	0	(577)
Ending balance	0	0	(1,541)
Gain on Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,501)	(7,424)	(6,403)
Change excluding amounts reclassified from accumulated other comprehensive loss	0	(1,379)	(1,063)
Amounts reclassified from accumulated other comprehensive loss	887	4,302	42
Cumulative effect adjustment of accounting standards		0
Net other comprehensive loss (income)	887	2,923	(1,021)
Ending balance	(3,614)	(4,501)	(7,424)
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	15,050	15,135	16,528
Change excluding amounts reclassified from accumulated other comprehensive loss	1,044	1,143	82
Amounts reclassified from accumulated other comprehensive loss	(1,197)	(1,228)	(1,475)
Cumulative effect adjustment of accounting standards		0
Net other comprehensive loss (income)	(153)	(85)	(1,393)
Ending balance	14,897	15,050	15,135
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	10,549	6,170	9,161
Change excluding amounts reclassified from accumulated other comprehensive loss	1,044	(236)	(2,209)
Amounts reclassified from accumulated other comprehensive loss	(310)	3,074	(782)
Cumulative effect adjustment of accounting standards		1,541
Net other comprehensive loss (income)	734	2,838	(2,991)
Ending balance	$ 11,283	$ 10,549	$ 6,170