Accumulated Other Comprehensive Income (Schedule of Items Reclassified to Statement of Income) (Details) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Expense related to interest rate swaps included in Income before taxes														$ 19,650	$ 20,242	$ 18,602
Total pretax amount reclassified														(178,212)	(115,247)	(54,708)
Income tax effect														44,829	32,228	22,123
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		$ (29,100)	$ (40,000)	$ (34,100)	$ (29,200)	$ (17,600)	$ (27,700)	$ (29,900)	$ (7,700)	$ (5,900)	$ (15,300)	$ (1,100)	$ (10,800)	(132,398)	(82,891)	(33,111)
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 before taxes	[1]													(1,011)	(146)	1,490
Income tax effect														259	37	(566)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income														(752)	(109)	924
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Settlements and Curtailments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total pretax amount reclassified														450	1,494
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]
Total pretax amount reclassified														(4,420)	(4,454)	(4,453)
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]
Total pretax amount reclassified														4,480	5,175	5,439
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	[2]													510	2,215	986
Income tax effect														(87)	(506)	(22)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income														$ 423	$ 1,709	$ 964

[1] Included in interest expense, net are payments related to the interest rate swap agreements and amortization of swap buyouts (see Notes 17 and 18).

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