Retirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 155	$ 190
Interest cost	302	368
Parent Company [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	155	190	$ 61
Interest cost	302	368	410
Expected return on plan assets	(355)	(389)	(393)
Amortization of prior service cost (credit)	6	0	0
Amortization of net loss (gain)	(39)	(82)	(374)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	69	87	(296)
Subsidiaries [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	155	190	61
Interest cost	302	368	410
Expected return on plan assets	(355)	(389)	(393)
Amortization of prior service cost (credit)	6	0	0
Amortization of net loss (gain)	(52)	(137)	(562)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	56	32	(484)
Nonqualified Plan | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	456	756
Interest cost	1,183	1,464
Nonqualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	456	756	1,023
Interest cost	1,183	1,464	2,314
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	349	349	331
Amortization of net loss (gain)	2,165	2,122	1,365
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	4,153	4,691	5,033
Nonqualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	456	756	1,023
Interest cost	1,183	1,464	2,314
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	349	349	333
Amortization of net loss (gain)	2,344	2,385	1,733
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	4,332	4,954	5,403
Qualified Plan | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,888	24,337
Interest cost	22,381	25,180
Qualified Plan | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,888	24,337	22,656
Interest cost	22,381	25,180	28,913
Expected return on plan assets	(48,239)	(49,902)	(50,249)
Amortization of prior service cost (credit)	(1,904)	(1,980)	(1,980)
Amortization of net loss (gain)	11,803	8,160	1,151
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	10,929	5,795	491
Qualified Plan | Subsidiaries [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	26,888	24,337	22,656
Interest cost	22,381	25,180	28,913
Expected return on plan assets	(48,242)	(49,910)	(50,267)
Amortization of prior service cost (credit)	(1,513)	(1,573)	(1,573)
Amortization of net loss (gain)	21,862	19,043	12,877
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ 21,376	$ 17,077	$ 12,606