Employee Postretirement Benefits - Reconciliation of Changes in Fair Value of Plan Assets and Plan's Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets, beginning balance	$ 360,678
Fair Value of Plan Assets, ending balance	387,212	$ 360,678
Pension Plan
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets, beginning balance	360,678	329,781
Actual Return on Plan Assets	32,816	35,474
Company Contributions	10,000	11,200
Benefit Payments	(16,282)	(15,777)
Participant Premium Payments	0	0
Fair Value of Plan Assets, ending balance	387,212	360,678	$ 329,781
Change in Benefit Obligation:
Projected Benefit Obligation, beginning balance	428,396	384,785
Service Cost	7,462	6,621	5,491
Interest Cost	11,660	13,053	14,412
Benefit Payments	(16,282)	(15,777)
Participant Premium Payments	0	0
Plan Amendments	0	0
Actuarial Loss (Gain)	(14,539)	39,714
Projected Benefit Obligation, ending balance	416,697	428,396	384,785
Funded Status	(29,485)	(67,718)
Amounts Recognized in Consolidated Balance Sheet at December 31:
Current Liabilities	0	0
Noncurrent Liabilities and Deferred Credits	(29,485)	(67,718)
Total Liabilities	(29,485)	(67,718)
Executive Survivor and Supplemental Retirement Plan
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets, beginning balance	0	0
Actual Return on Plan Assets	0	0
Company Contributions	1,562	1,505
Benefit Payments	(1,562)	(1,505)
Participant Premium Payments	0	0
Fair Value of Plan Assets, ending balance	0	0	0
Change in Benefit Obligation:
Projected Benefit Obligation, beginning balance	47,894	43,966
Service Cost	187	179	418
Interest Cost	1,228	1,449	1,735
Benefit Payments	(1,562)	(1,505)
Participant Premium Payments	0	0
Plan Amendments	0	0
Actuarial Loss (Gain)	(907)	3,805
Projected Benefit Obligation, ending balance	46,840	47,894	43,966
Funded Status	(46,840)	(47,894)
Amounts Recognized in Consolidated Balance Sheet at December 31:
Current Liabilities	(2,352)	(1,557)
Noncurrent Liabilities and Deferred Credits	(44,488)	(46,337)
Total Liabilities	(46,840)	(47,894)
Other Postretirement Benefits Plan
Change in Fair Value of Plan Assets:
Fair Value of Plan Assets, beginning balance	0	0
Actual Return on Plan Assets	0	0
Company Contributions	2,695	2,662
Benefit Payments	(8,385)	(6,694)
Participant Premium Payments	5,690	4,032
Fair Value of Plan Assets, ending balance	0	0	0
Change in Benefit Obligation:
Projected Benefit Obligation, beginning balance	70,185	71,437
Service Cost	1,722	1,847	1,286
Interest Cost	1,891	2,393	3,083
Benefit Payments	(8,385)	(6,694)
Participant Premium Payments	5,690	4,032
Plan Amendments	0	(3,891)
Actuarial Loss (Gain)	(1,792)	1,061
Projected Benefit Obligation, ending balance	69,311	70,185	$ 71,437
Funded Status	(69,311)	(70,185)
Amounts Recognized in Consolidated Balance Sheet at December 31:
Current Liabilities	(2,830)	(2,826)
Noncurrent Liabilities and Deferred Credits	(66,481)	(67,359)
Total Liabilities	$ (69,311)	$ (70,185)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.