Retirement Benefit Plans - Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss (gain)	$ 18,319	$ (12,052)	$ 5,262
Amounts reclassified from (AOCL) AOCI	(2,210)	(4,102)	(3,976)
Total loss (gain) recognized in (OCL) OCI	16,109	(16,154)	1,286
Pension
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss (gain)	17,148	(12,008)	5,375
Amounts reclassified from (AOCL) AOCI	(2,224)	(4,102)	(4,027)
Total loss (gain) recognized in (OCL) OCI	14,924	(16,110)	1,348
SERP
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss (gain)	(581)	(77)	194
Amounts reclassified from (AOCL) AOCI	(26)	(38)	(23)
Total loss (gain) recognized in (OCL) OCI	(607)	(115)	171
OPEB
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss (gain)	(4,992)	33	(307)
Amounts reclassified from (AOCL) AOCI	40	38	74
Total loss (gain) recognized in (OCL) OCI	$ (4,952)	$ 71	$ (233)