Accumulated Other Comprehensive Income (Schedule of Items Reclassified to Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost/(credit)													$ 3,905		$ 3,631	$ 3,629
Amortization of transition obligation													(70)		(79)	(83)
Amortization of net actuarial loss													(6,512)		(7,438)	(8,694)
Swap interest expense													15,227		18,118	20,148
Total pretax amount reclassified													(31,076)		68,366	(53,848)
Income tax expense/(benefit)													13,372		(27,523)	32,582
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(8,700)	(4,700)	7,400	(11,500)	(8,200)	(9,500)	33,700	(47,000)	7,200	(16,700)	(8,800)	(16,700)	(17,517)		(30,977)	(34,938)
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													1,900
Income tax expense/(benefit)													(741)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income													1,159
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)													(3,905)
Amortization of transition obligation													70
Amortization of net actuarial loss													6,512
Total pretax amount reclassified													2,677	[1]
Income tax expense/(benefit)													(451)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income													$ 2,226

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 5).