Employee Benefit Plans and Other Postretirement Benefits - Schedule Of Obligation And Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Prepaid pension costs	$ 56,014	$ 0
Pension and SERPA Benefits
Change in benefit obligation:
Benefit obligation, beginning of period	1,984,708	2,201,021
Service cost	25,408	32,340	$ 31,584
Interest cost	85,483	82,778	85,076
Actuarial losses (gains)	236,719	(213,583)
Plan participant contributions	0	0
Plan amendments	8,371	(12,926)
Special early retirement benefits	1,583	0
Benefits paid	(126,079)	(106,280)
Net curtailments and settlements	(4,181)	1,358
Benefit obligation, end of period	2,212,012	1,984,708	2,201,021
Change in plan assets:
Fair value of plan assets, beginning of period	1,874,618	2,162,885
Return on plan assets	459,388	(185,468)
Plan participant contributions	0	0
Benefits paid	(124,784)	(102,799)
Fair value of plan assets, end of period	2,209,222	1,874,618	2,162,885
Funded status of the plan	(2,790)	(110,090)
Prepaid pension costs	56,014	0
Accrued liabilities	(2,666)	(2,314)
Pension and Postretirement healthcare liabilities	(56,138)	(107,776)
Net amount recognized	(2,790)	(110,090)
Prior service credits	(6,489)	(14,371)
Actuarial losses (gains)	496,919	593,608
Amounts included in other comprehensive income, net of tax	490,430	579,237
Postretirement Health Coverage
Change in benefit obligation:
Benefit obligation, beginning of period	286,574	338,488
Service cost	4,449	7,180	7,500
Interest cost	11,753	11,556	13,648
Actuarial losses (gains)	9,590	(42,039)
Plan participant contributions	1,999	2,492
Plan amendments	0	(4,710)
Special early retirement benefits	0	0
Benefits paid	(20,860)	(23,448)
Net curtailments and settlements	0	(2,945)
Benefit obligation, end of period	293,505	286,574	338,488
Change in plan assets:
Fair value of plan assets, beginning of period	190,357	217,537
Return on plan assets	41,717	(13,287)
Plan participant contributions	1,999	2,492
Benefits paid	(13,081)	(16,385)
Fair value of plan assets, end of period	220,992	190,357	$ 217,537
Funded status of the plan	(72,513)	(96,217)
Prepaid pension costs	0	0
Accrued liabilities	0	(1,764)
Pension and Postretirement healthcare liabilities	(72,513)	(94,453)
Net amount recognized	(72,513)	(96,217)
Prior service credits	(7,559)	(9,381)
Actuarial losses (gains)	(1,321)	12,005
Amounts included in other comprehensive income, net of tax	$ (8,880)	$ 2,624