Accumulated Other Comprehensive Income (AOCI) (Schedule of Items Reclassified to Statement of Income) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Expense related to interest rate swaps included in Income		$ 4,328	$ 2,238
Total pretax amount reclassified (b)		17,524	20,359
Income tax effect		6,550	7,043
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		(10,839)	(13,501)
Prior service credit		(1,113)	(1,113)
Net actuarial loss		1,347	1,278
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivative valuation adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Expense related to interest rate swaps included in Income	[1]	600	281
Income tax effect		(228)	(107)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		372	174
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and postretirement liability adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified (b)	[2]	234	165
Income tax effect		(70)	(49)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		$ 164	$ 116

[1] Included in Interest expense are payments related to the interest rate swap agreements and amortization of swap buyouts (see Note 15).

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