Retirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 217	$ 155
Interest cost	311	302
Parent Company [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	217	155	$ 190
Interest cost	311	302	368
Expected return on plan assets	(379)	(355)	(389)
Amortization of prior service cost (credit)	22	6	0
Amortization of net loss (gain)	(29)	(39)	(82)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	142	69	87
Subsidiaries [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	217	155	190
Interest cost	311	302	368
Expected return on plan assets	(379)	(355)	(389)
Amortization of prior service cost (credit)	22	6	0
Amortization of net loss (gain)	(35)	(52)	(137)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	136	56	32
Nonqualified Plan | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	557	456
Interest cost	1,253	1,183
Nonqualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	557	456	756
Interest cost	1,253	1,183	1,464
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	289	349	349
Amortization of net loss (gain)	2,471	2,165	2,122
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	4,570	4,153	4,691
Nonqualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	557	456	756
Interest cost	1,253	1,183	1,464
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	289	349	349
Amortization of net loss (gain)	2,648	2,344	2,385
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	4,747	4,332	4,954
Qualified Plan | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,351	26,888
Interest cost	24,263	22,381
Qualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,351	26,888	24,337
Interest cost	24,263	22,381	25,180
Expected return on plan assets	(51,014)	(48,239)	(49,902)
Amortization of prior service cost (credit)	0	(1,904)	(1,980)
Amortization of net loss (gain)	6,381	11,803	8,160
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	5,981	10,929	5,795
Qualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,351	26,888	24,337
Interest cost	24,263	22,381	25,180
Expected return on plan assets	(51,016)	(48,242)	(49,910)
Amortization of prior service cost (credit)	0	(1,513)	(1,573)
Amortization of net loss (gain)	15,080	21,862	19,043
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 14,678	$ 21,376	$ 17,077