Summary Of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,809,842)	$ (1,716,896)	$ (1,545,010)
Cumulative effect adjustment of accounting standards (see Note 2)	(1,541)	0	0
Net other comprehensive loss (income)	2,838	(2,991)	1,517
Ending balance	(1,750,699)	(1,809,842)	(1,716,896)
Gain on Investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,541)	(964)
Cumulative effect adjustment of accounting standards (see Note 2)	(1,541)
Change excluding amounts reclassified from accumulated other comprehensive loss	0	(1,228)
Amounts reclassified from accumulated other comprehensive loss	0	651
Net other comprehensive loss (income)	0	(577)
Ending balance	0	(1,541)	(964)
Gain on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7,424)
Change excluding amounts reclassified from accumulated other comprehensive loss	(1,379)
Amounts reclassified from accumulated other comprehensive loss	4,302
Net other comprehensive loss (income)	2,923
Ending balance	(4,501)	(7,424)
Gain on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7,424)	(6,403)
Change excluding amounts reclassified from accumulated other comprehensive loss		(1,063)
Amounts reclassified from accumulated other comprehensive loss		42
Net other comprehensive loss (income)		(1,021)
Ending balance		(7,424)	(6,403)
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	15,135	16,528
Change excluding amounts reclassified from accumulated other comprehensive loss	1,143	82
Amounts reclassified from accumulated other comprehensive loss	(1,228)	(1,475)
Net other comprehensive loss (income)	(85)	(1,393)
Ending balance	15,050	15,135	16,528
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,170	9,161	7,644
Cumulative effect adjustment of accounting standards (see Note 2)	(1,541)
Change excluding amounts reclassified from accumulated other comprehensive loss	(236)	(2,209)
Amounts reclassified from accumulated other comprehensive loss	3,074	(782)
Net other comprehensive loss (income)	2,838	(2,991)	1,517
Ending balance	$ 10,549	$ 6,170	$ 9,161