Summary of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (1,750,699)	$ (1,809,842)	$ (1,809,842)
Cumulative effect adjustment of accounting standards	0	1,541
Net other comprehensive loss (income)	(69)	1,983
Ending Balance	(1,760,434)	(1,906,343)	(1,750,699)
Gain on Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	(1,541)	(1,541)
Cumulative effect adjustment of accounting standards			1,541
Change excluding amounts reclassified from accumulated other comprehensive loss
Amounts reclassified from accumulated other comprehensive loss
Net other comprehensive loss (income)	0	0
Ending Balance	0	0	0
Gain on Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(4,501)	(7,424)	(7,424)
Change excluding amounts reclassified from accumulated other comprehensive loss		(1,379)
Amounts reclassified from accumulated other comprehensive loss	219	3,633
Net other comprehensive loss (income)	219	2,254
Ending Balance	(4,282)	(5,170)	(4,501)
Defined Benefit Pension Plan [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	15,050	15,135	15,135
Amounts reclassified from accumulated other comprehensive loss	(288)	(271)
Net other comprehensive loss (income)	(288)	(271)
Ending Balance	14,762	14,864	15,050
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	10,549	6,170	6,170
Cumulative effect adjustment of accounting standards			1,541
Change excluding amounts reclassified from accumulated other comprehensive loss		(1,379)
Amounts reclassified from accumulated other comprehensive loss	(69)	3,362
Net other comprehensive loss (income)	(69)	1,983
Ending Balance	$ 10,480	$ 9,694	$ 10,549