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, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified	$ (18,393)		$ 9,271		$ (36,543)		$ (8,488)
Income tax effect	7,216		(2,243)		14,673		4,005
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(11,219)		7,379		(21,840)		(4,132)
Derivative Valuation Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Payments made on interest rate swaps included in earnings	473		454		951		910
Income tax effect	(184)		(177)		(371)		(354)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	289		277		580		556
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified	(1,108)		(909)		(2,217)		(1,817)
Accumulated Defined Benefit Plans Adjustment, Net Transition Asset (Obligation) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified			17				34
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified	1,355		1,664		2,683		3,328
Pension and Postretirement Liability Adjustments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified	247	[1]	772	[1]	466	[1]	1,545	[1]
Income tax effect	(98)		(271)		(186)		(541)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 149		$ 501		$ 280		$ 1,004

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