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, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified	$ (18,536)		$ (7,079)		$ (55,079)		$ (15,567)
Income tax effect	6,762		2,381		21,435		6,386
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(11,812)		(4,698)		(33,652)		(8,830)
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	480		467		1,431		1,377
Income tax effect	(187)		(183)		(558)		(537)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	293		284		873		840
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)		(974)		(3,325)		(2,791)
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				51
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	1,343		1,635		4,026		4,963
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	235	[1]	678	[1]	701	[1]	2,223	[1]
Income tax effect	(94)		(265)		(280)		(806)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 141		$ 413		$ 421		$ 1,417

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