Retirement Benefit Plans - Changes in Plan Assets and Funded Status of Pension Plans and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jul. 01, 2021
Change in plan assets:
Beginning balance	$ 271,846
Ending balance	201,382	$ 271,846
Funded status of the plan at year end				$ 2,100
Pension
Change in benefit obligation:
Beginning balance	250,263	266,414
Service cost	0	0	$ 0
Interest cost	5,565	4,663	6,511
Actuarial (gain) loss	(57,751)	(11,131)
Benefits and administrative expenses paid	(10,241)	(9,683)
Benefit obligation assumed from Sterling	0	0
Ending balance	187,836	250,263	266,414
Change in plan assets:
Beginning balance	271,846	266,268
Actual return on plan assets	(60,223)	15,261
Employer contributions	0	0
Benefits paid	(10,241)	(9,683)
Ending balance	201,382	271,846	266,268
Funded status of the plan at year end	13,546	21,583
SERP
Change in benefit obligation:
Beginning balance	1,873	2,046
Service cost	0	0	0
Interest cost	107	30	46
Actuarial (gain) loss	(581)	(77)
Benefits and administrative expenses paid	(1,671)	(126)
Benefit obligation assumed from Sterling	4,517	0
Ending balance	4,245	1,873	2,046
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	1,671	126
Benefits paid	(1,671)	(126)
Ending balance	0	0	0
Funded status of the plan at year end	(4,245)	(1,873)
OPEB
Change in benefit obligation:
Beginning balance	1,904	1,998
Service cost	34	0	0
Interest cost	652	19	46
Actuarial (gain) loss	(4,992)	32
Benefits and administrative expenses paid	(806)	(145)
Benefit obligation assumed from Sterling	26,030	0
Ending balance	22,822	1,904	1,998
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	806	145
Benefits paid	(806)	(145)
Ending balance	0	0	$ 0
Funded status of the plan at year end	$ (22,822)	$ (1,904)