Accumulated Other Comprehensive Income (AOCI) (Schedule of Items Reclassified to Statement of Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Expense related to interest rate swaps included in Income before taxes	$ 5,218	$ 5,059	$ 10,234	$ 9,729
Total pretax amount reclassified	48,664	36,809	85,548	48,073
Income tax effect	14,405	6,966	21,881	10,331
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(34,054)	(29,902)	(63,244)	(37,564)
Pension/postretirement curtailment		(518)		(518)
Prior service credit	(1,105)	(1,113)	(2,210)	(2,227)
Net actuarial loss	1,118	1,291	2,239	2,588
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	(420)	54	(872)	234
Income tax effect	107	(13)	223	(56)
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	(313)	41	(649)	178
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	13	(340)	29	(157)
Income tax effect	(4)	102	(9)	47
Effect on net income due to items reclassified from Accumulated Other Comprehensive Income	$ 9	$ (238)	$ 20	$ (110)