v3.25.2
Retirement Benefit Obligations - Components of Retirement Plan Costs (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 436 $ 497 $ 872 $ 994
Interest Cost 2,016 1,886 4,032 3,772
Expected Return on Plan Assets (2,625) (2,649) (5,249) (5,298)
Prior Service Cost Amortization 64 81 128 162
Actuarial Loss Amortization 319 362 638 724
Sub-total 210 177 421 354
Amounts Capitalized and Deferred 26 27 135 135
Net Periodic Benefit Cost Recognized 236 204 556 489
Other Postretirement Benefits Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 501 497 1,003 994
Interest Cost 992 817 1,984 1,634
Expected Return on Plan Assets (1,085) (969) (2,171) (1,938)
Prior Service Cost Amortization 0 0 0 0
Actuarial Loss Amortization (187) (218) (374) (437)
Sub-total 221 127 442 253
Amounts Capitalized and Deferred (48) 54 (34) 178
Net Periodic Benefit Cost Recognized 173 181 408 431
Supplemental Employee Retirement Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 40 55 79 109
Interest Cost 172 181 344 362
Expected Return on Plan Assets 0 0 0 0
Prior Service Cost Amortization 2 2 4 4
Actuarial Loss Amortization (54) 0 (107) 0
Sub-total 160 238 320 475
Amounts Capitalized and Deferred (50) (74) (101) (148)
Net Periodic Benefit Cost Recognized $ 110 $ 164 $ 219 $ 327