Accumulated Other Comprehensive Income (AOCI) (Schedule of Items Reclassified to Statement of Income) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Payments made on interest rate swaps included in income before taxes		$ 3,681	$ 2,671	$ 9,610	$ 8,049
Income before income taxes		20,897	21,923	57,439	40,197
Income tax effect		7,488	12,243	20,613	20,398
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		(13,069)	(9,658)	(36,937)	(19,699)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative Valuation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Payments made on interest rate swaps included in income before taxes	[1]	1,100	587	1,686	1,540
Income tax effect		(418)	(229)	(641)	(601)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		682	358	1,045	939
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and Postretirement Liability Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[2]	183	352	532	1,098
Income tax effect		(55)	(123)	(160)	(384)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		128	229	372	714
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes		(1,113)	(1,110)	(3,338)	(3,330)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes		$ 1,296	$ 1,462	$ 3,870	$ 4,428

[1] Included in Interest expense.

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