Employee Benefit Plans and Other Postretirement Benefits - Components Of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension and SERPA Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 27,224	$ 25,408	$ 32,340
Interest cost	76,447	85,483	82,778
Expected return on plan assets	(135,056)	(142,323)	(147,671)
Prior service credit	(1,088)	(1,930)	(420)
Net loss	65,489	44,511	64,773
Special early retirement benefits	0	1,583	0
Curtailment loss (gain)	74	0	1,017
Settlement loss	2,742	1,503	0
Net periodic benefit cost	35,832	14,235	32,817
Postretirement Health Coverage
Defined Benefit Plan Disclosure [Line Items]
Service cost	11,761	4,449	7,180
Interest cost	9,391	11,753	11,556
Expected return on plan assets	(13,870)	(14,030)	(14,161)
Prior service credit	(2,381)	(2,381)	(1,842)
Net loss	492	277	1,817
Special early retirement benefits	0	0	0
Curtailment loss (gain)	(392)	(960)	(886)
Settlement loss	0	0	0
Net periodic benefit cost	$ 5,001	$ (892)	$ 3,664