Pension Plan and Employee Benefits - Benefit Obligation, Plan Assets, and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
PENSION BENEFITS
Change in benefit obligation
Benefit obligation at beginning of period	$ 680,417	$ 686,384
Service cost	8,589	10,516	$ 9,820
Interest cost	19,841	18,668	20,816
Plan participants’ contributions	0	0
Actuarial gain	(174,733)	(9,823)
Expenses paid	(3,744)	(3,306)
Benefits paid	(29,501)	(25,292)
Special/contractual termination benefits	0	3,270	0
Benefit obligation at end of period	500,869	680,417	686,384
Change in plan assets
Fair value of plan assets at beginning of period	527,427	516,120
Actual (loss) gain return on plan assets	(91,897)	39,905
Expenses paid	(3,744)	(3,306)
Benefits paid	(29,501)	(25,292)
Fair value of plan assets at end of period	402,285	527,427	516,120
Unfunded status	(98,584)	(152,990)
Accumulated benefit obligation	481,398	640,490
OTHER BENEFITS
Change in benefit obligation
Benefit obligation at beginning of period	55,257	56,331
Service cost	2,204	2,425	2,153
Interest cost	1,484	1,283	1,651
Plan participants’ contributions	1,904	0
Actuarial gain	(10,289)	(81)
Expenses paid	0	0
Benefits paid	(7,254)	(4,701)
Special/contractual termination benefits	0	0	0
Benefit obligation at end of period	43,306	55,257	56,331
Change in plan assets
Fair value of plan assets at beginning of period	0	0
Actual (loss) gain return on plan assets	0	0
Expenses paid	0	0
Benefits paid	0	0
Fair value of plan assets at end of period	0	0	0
Unfunded status	(43,306)	(55,257)
SERP BENEFITS
Change in benefit obligation
Benefit obligation at beginning of period	93,179	97,225
Service cost	227	232	399
Interest cost	2,679	2,538	2,932
Actuarial gain	(22,097)	(1,932)
Benefits paid	(5,561)	(4,884)
Benefit obligation at end of period	68,427	93,179	$ 97,225
Change in plan assets
Accumulated benefit obligation	$ 68,427	$ 93,179