Postretirement Benefits - Pension and SERP Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	$ 743,586	$ 778,934
Nonqualified Plan \| SERP
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	91,725	92,017
Funded defined benefit pension \| Qualified Plan \| Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	$ 651,861	$ 686,917

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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