Accumulated Other Comprehensive Income (Schedule of Items Reclassified to Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost/(credit)	$ 974	$ 595	$ 2,791	$ 2,412
Amortization of transition obligation	(17)	(22)	(51)	(59)
Amortization of net actuarial loss	(1,635)	(1,739)	(4,963)	(6,186)
Total pretax amount reclassified	(7,079)	(16,046)	(15,567)	81,473
Income tax effect	2,381	6,965	6,386	(32,650)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(4,698)	(9,463)	(8,830)	(22,759)
Derivative Valuation Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Swap interest expense	500		1,400
Income tax effect	(195)		(546)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	305		854
Pension and Postretirement Liability Adjustments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost/(credit)	(974)		(2,791)
Amortization of transition obligation	17		51
Amortization of net actuarial loss	1,635		4,963
Total pretax amount reclassified	678		2,223
Income tax effect	(265)		(806)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 413		$ 1,417