Retirement Benefits - Amounts Recognized (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 11,654	$ 12,114	$ 11,627
Accumulated benefit obligation	11,549	12,070
Fair value of plan assets	6,341	5,918	6,289
Defined Benefit Plan, Amounts Recognized in Statement of Financial Position Consist of: [Abstract]
Noncurrent assets	0	0
Current liabilities	(280)	(293)
Noncurrent liabilities	(5,033)	(5,903)
Net assets (liabilities)	(5,313)	(6,196)
Parent Company [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	(525)	600
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	242	44
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	(283)	644
Subsidiaries [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	(622)	489
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	242	44
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	(380)	533
Nonqualified Plan | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	43,155	46,742	63,000
Accumulated benefit obligation	40,773	44,033
Fair value of plan assets	0	0	0
Defined Benefit Plan, Amounts Recognized in Statement of Financial Position Consist of: [Abstract]
Noncurrent assets	0	0
Current liabilities	(2,822)	(6,763)
Noncurrent liabilities	(40,333)	(39,979)
Net assets (liabilities)	(43,155)	(46,742)
Nonqualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	9,571	11,738
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	578	927
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	10,149	12,665
Nonqualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	10,103	12,504
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	578	927
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	10,681	13,431
Qualified Plan | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	834,960	849,383	774,305
Accumulated benefit obligation	823,418	837,455
Fair value of plan assets	898,550	834,655	$ 753,042
Defined Benefit Plan, Amounts Recognized in Statement of Financial Position Consist of: [Abstract]
Noncurrent assets	63,590	0
Current liabilities	0	0
Noncurrent liabilities	0	(14,728)
Net assets (liabilities)	63,590	(14,728)
Qualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	24,859	98,010
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	0	(1,904)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	24,859	96,106
Qualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Amounts Recognized in Accumulated Other Comprehensive Income Consist of: [Abstract]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	127,111	210,317
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	0	(1,513)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Total	$ 127,111	$ 208,804