Accumulated Other Comprehensive Income (Schedule of Items Reclassified to Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost/(credit)	$ 1,109		$ 908
Amortization of transition obligation			(17)
Amortization of net actuarial loss	(1,328)		(1,664)
Total pretax amount reclassified	(18,150)		(17,759)
Income tax effect	7,457		6,248
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(10,621)		(11,511)
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	478		456
Income tax effect	(186)		(178)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	292		278
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)	(1,109)		(908)
Amortization of transition obligation			17
Amortization of net actuarial loss	1,328		1,664
Total pretax amount reclassified	219	[1]	773	[1]
Income tax effect	(88)		(270)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 131		$ 503

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 4).