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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Expense related to interest rate swaps included in Income before taxes		$ 4,838	$ 5,200	$ 15,072	$ 14,929
Total pretax amount reclassified		53,319	39,364	138,867	87,437
Income tax effect		13,194	11,359	35,075	21,690
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		(40,009)	(27,736)	(103,253)	(65,300)
Pension/postretirement curtailment			232		750
Prior service credit		(1,105)	(1,114)	(3,315)	(3,341)
Net actuarial loss		1,118	1,294	3,357	3,882
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]	(245)	(96)	(1,117)	138
Income tax effect		62	23	285	(33)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		(183)	(73)	(832)	105
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]	13	(52)	42	(209)
Income tax effect		(4)	16	(3)	63
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income		$ 9	$ (36)	$ 29	$ (146)

[1] Included in Interest expense, net, are payments related to the interest rate swap agreements and amortization of swap buyouts (see Notes 15 and 16).

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