Employee Benefit Plans and Other Postretirement Benefits - Schedule Of Obligation And Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets:
Pension and postretirement assets	$ 95,711	$ 56,014
Pension and SERPA Benefits
Change in benefit obligation:
Benefit obligation, beginning of period	2,212,012	1,984,708
Service cost	27,224	25,408	$ 32,340
Interest cost	76,447	85,483	82,778
Actuarial losses (gains)	228,081	236,719
Plan participant contributions	0	0
Plan amendments	0	8,371
Special early retirement benefits	0	1,583
Benefits paid	(137,381)	(126,079)
Net curtailments and settlements	(15,948)	(4,181)
Benefit obligation, end of period	2,390,435	2,212,012	1,984,708
Change in plan assets:
Fair value of plan assets, beginning of period	2,209,222	1,874,618
Return on plan assets	361,674	459,388
Plan participant contributions	0	0
Benefits paid	(136,921)	(124,784)
Fair value of plan assets, end of period	2,433,975	2,209,222	1,874,618
Funded status of the plan	43,540	(2,790)
Pension and postretirement assets	82,537	56,014
Accrued liabilities	(8,814)	(2,666)
Pension and Postretirement healthcare liabilities	(30,183)	(56,138)
Total benefits included in balance sheet	43,540	(2,790)
Prior service credits	(5,712)	(6,489)
Actuarial losses (gains)	445,804	496,919
Amounts included in other comprehensive income, net of tax	440,092	490,430
Postretirement Health Coverage
Change in benefit obligation:
Benefit obligation, beginning of period	293,505	286,574
Service cost	11,761	4,449	7,180
Interest cost	9,391	11,753	11,556
Actuarial losses (gains)	18,824	9,590
Plan participant contributions	2,140	1,999
Plan amendments	0	0
Special early retirement benefits	0	0
Benefits paid	(19,703)	(20,860)
Net curtailments and settlements	(673)	0
Benefit obligation, end of period	315,245	293,505	286,574
Change in plan assets:
Fair value of plan assets, beginning of period	220,992	190,357
Return on plan assets	36,349	41,717
Plan participant contributions	2,140	1,999
Benefits paid	(15,446)	(13,081)
Fair value of plan assets, end of period	244,035	220,992	$ 190,357
Funded status of the plan	(71,210)	(72,513)
Pension and postretirement assets	13,174	0
Accrued liabilities	(361)	0
Pension and Postretirement healthcare liabilities	(84,023)	(72,513)
Total benefits included in balance sheet	(71,210)	(72,513)
Prior service credits	(5,438)	(7,559)
Actuarial losses (gains)	(4,942)	(1,321)
Amounts included in other comprehensive income, net of tax	$ (10,380)	$ (8,880)