Retirement Benefits - Change in Net Benefit Obligation and Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Other Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$ 12,114	$ 11,627
Amendments	205	44
Service cost	155	190
Interest cost	302	368
Actuarial loss (gain)	514	(604)
Benefits paid	803	906
Medicare part D subsidy received	195	187
Administrative expense	0	0
Benefit obligation at end of period	11,654	12,114
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	5,918	6,289
Actual return on plan assets	1,005	278
Employer contribution	222	257
Benefits paid	(804)	(906)
Administrative expense	0	0
Fair value of plan assets at end of period	6,341	5,918
Funded status at end of period	(5,313)	(6,196)
Nonqualified Plan | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	46,742	63,000
Amendments	0	0
Service cost	456	756
Interest cost	1,183	1,464
Actuarial loss (gain)	(828)	(3,663)
Benefits paid	6,054	22,141
Medicare part D subsidy received	0	0
Administrative expense	0	0
Benefit obligation at end of period	43,155	46,742
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Employer contribution	6,054	22,141
Benefits paid	(6,054)	(22,141)
Administrative expense	0	0
Fair value of plan assets at end of period	0	0
Funded status at end of period	(43,155)	(46,742)
Qualified Plan | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	849,383	774,305
Amendments	0	0
Service cost	26,888	24,337
Interest cost	22,381	25,180
Actuarial loss (gain)	6,826	(69,413)
Benefits paid	55,831	42,775
Medicare part D subsidy received	0	0
Administrative expense	(1,035)	(1,077)
Benefit obligation at end of period	834,960	849,383
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	834,655	753,042
Actual return on plan assets	102,787	107,409
Employer contribution	18,000	18,000
Benefits paid	(55,831)	(42,775)
Administrative expense	(1,061)	(1,021)
Fair value of plan assets at end of period	898,550	834,655
Funded status at end of period	$ 63,590	$ (14,728)