Components of Accumulated Other Comprehensive Income (Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		$ 2,153,272	$ 2,228,263	$ 2,171,098	$ 2,263,153
Reclassifications from AOCI to earnings:
Balance, end of period		2,112,599	2,233,169	2,112,599	2,233,169
Pension and Other Postretirement Employee Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		(19,154)	(28,625)	(18,925)	(28,494)
Reclassifications from AOCI to earnings:
Other	[1]	(305)	(176)	(611)	(352)
Tax effect		75	43	152	88
Net of tax amount		(230)	(133)	(459)	(264)
Other reclassifications		0	(211)	0	(211)
Balance, end of period		(19,384)	(28,969)	(19,384)	(28,969)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		137,882	108,811	121,957	126,146
Unrecognized gains (losses) arising in AOCI during the period:
Gross		9,325	22,754	31,197	8,873
Tax effect		(141)	(462)	(493)	(172)
Reclassifications from AOCI to earnings:
Gross	[2]	(5,697)	(4,726)	(11,416)	(8,563)
Tax effect		124	108	248	201
Net of tax amount		3,611	17,674	19,536	339
Other reclassifications		0	45	0	45
Balance, end of period		141,493	126,530	141,493	126,530
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, beginning of period		118,728	80,186	103,032	97,652
Reclassifications from AOCI to earnings:
Balance, end of period		$ 122,109	$ 97,561	$ 122,109	$ 97,561

[1] Included in the computation of net periodic pension costs.

[2] Included in Interest expense, net on the Condensed Consolidated Statement of Operations.