Retirement Benefits Change in Net Benefit Obligation (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Beginning Balance	$ 849,383	$ 774,305
Defined Benefit Plan, Service Cost	20,166	24,337
Defined Benefit Plan, Interest Cost	16,786	25,180
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	4,580	69,413
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(37,807)	(42,775)
Defined Benefit Plan, Benefit Obligation, Prescription Drug Subsidy Receipt	0	0
defined benefit plan expected administration expense	0	1,077
Defined Benefit Plan, Benefit Obligation, Ending Balance	853,108	849,383
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Beginning Balance	46,742	63,000
Defined Benefit Plan, Service Cost	344	756
Defined Benefit Plan, Interest Cost	879	1,464
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(630)	3,663
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(1,485)	(22,141)
Defined Benefit Plan, Benefit Obligation, Prescription Drug Subsidy Receipt	0	0
defined benefit plan expected administration expense	0	0
Defined Benefit Plan, Benefit Obligation, Ending Balance	45,850	46,742
Other Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Beginning Balance	12,114	11,627
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	(44)
Defined Benefit Plan, Service Cost	117	190
Defined Benefit Plan, Interest Cost	226	368
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(80)	604
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(669)	(906)
Defined Benefit Plan, Benefit Obligation, Prescription Drug Subsidy Receipt	195	187
defined benefit plan expected administration expense	0	0
Defined Benefit Plan, Benefit Obligation, Ending Balance	11,903	12,114
Qualified Plan [Member] | Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	0
Nonqualified Plan [Member] | Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	$ 0	$ 0