Postretirement Benefits - Pension and SERP Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 647,434	$ 627,560
Qualified Plan \| Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	574,981	554,957
Nonqualified Plan \| SERP
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 72,453	$ 72,603

Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant