v3.26.1
Retirement Benefit Obligations - Components of Retirement Plan Costs (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 405 $ 436 $ 809 $ 872
Interest Cost 2,004 2,016 4,009 4,032
Expected Return on Plan Assets (2,860) (2,625) (5,719) (5,249)
Prior Service Cost Amortization 92 64 184 128
Actuarial Loss Amortization 83 319 165 638
Sub-total (276) 210 (552) 421
Amounts Capitalized and Deferred 245 26 584 135
Net Periodic Benefit Cost Recognized (31) 236 32 556
Retirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 518 501 1,036 1,003
Interest Cost 1,163 992 2,326 1,984
Expected Return on Plan Assets (1,210) (1,085) (2,421) (2,171)
Prior Service Cost Amortization 0 0 0 0
Actuarial Loss Amortization (21) (187) (41) (374)
Sub-total 450 221 900 442
Amounts Capitalized and Deferred (147) (48) (226) (34)
Net Periodic Benefit Cost Recognized 303 173 674 408
Supplemental Employee Retirement Plans, Defined Benefit        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 44 40 89 79
Interest Cost 174 172 347 344
Expected Return on Plan Assets 0 0 0 0
Prior Service Cost Amortization 0 2 0 4
Actuarial Loss Amortization 0 (54) 0 (107)
Sub-total 218 160 436 320
Amounts Capitalized and Deferred (68) (50) (136) (101)
Net Periodic Benefit Cost Recognized $ 150 $ 110 $ 300 $ 219