Accumulated Other Comprehensive Income (Schedule of Items Reclassified to Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost/(credit)	$ 909	$ 909	$ 1,817	$ 1,817
Amortization of transition obligation	(17)	(18)	(34)	(37)
Amortization of net actuarial loss	(1,664)	(1,870)	(3,328)	(4,447)
Total pretax amount reclassified	9,271	87,418	(8,488)	97,519
Income tax effect	(2,243)	(29,643)	4,005	(39,615)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	7,379	33,745	(4,132)	(13,296)
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)		(900)
Income tax effect	(195)		(351)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(305)		(549)
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)	(908)		(1,817)
Amortization of transition obligation	17		34
Amortization of net actuarial loss	1,664		3,328
Total pretax amount reclassified	773		1,545
Income tax effect	(270)		(541)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 503		$ 1,004