Summary Of Significant Accounting Policies (Schedule Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,545,010)	$ (1,638,943)	$ (1,687,978)
Net other comprehensive loss (income)	1,517	(4,792)	8,234
Ending balance	(1,716,896)	(1,545,010)	(1,638,943)
Gain On Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(557)	(656)
Change excluding amounts reclassified from accumulated other comprehensive loss	(407)	99
Amounts reclassified from accumulated other comprehensive loss
Net other comprehensive loss (income)	(407)	99
Ending balance	(964)	(557)	(656)
Gain On Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(8,160)	(3,416)
Change excluding amounts reclassified from accumulated other comprehensive loss	3,288	(1,946)
Amounts reclassified from accumulated other comprehensive loss	(1,531)	(2,798)
Net other comprehensive loss (income)	1,757	(4,744)
Ending balance	(6,403)	(8,160)	(3,416)
Defined Benefit Pension Plan [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	16,361	16,508
Change excluding amounts reclassified from accumulated other comprehensive loss	1,719	1,276
Amounts reclassified from accumulated other comprehensive loss	(1,552)	(1,423)
Net other comprehensive loss (income)	167	(147)
Ending balance	16,528	16,361	16,508
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	7,644	12,436	4,202
Change excluding amounts reclassified from accumulated other comprehensive loss	4,600	(571)
Amounts reclassified from accumulated other comprehensive loss	(3,083)	(4,221)
Net other comprehensive loss (income)	1,517	(4,792)	8,234
Ending balance	$ 9,161	$ 7,644	$ 12,436