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Components of Retirement Plan Costs (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost $ 3,165 $ 3,472 $ 3,322
Interest Cost 5,486 5,003 5,776
Expected Return on Plan Assets 10,883 9,693 9,019
Prior Service Cost Amortization 356 301 320
Actuarial Loss Amortization $ (5,507) (8,089) (6,472)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Other Nonoperating Income (Expense)    
Sub-total $ 3,631 7,172 6,871
Amounts Capitalized or Deferred 1,085 3,384 3,083
NPBC Recognized 2,546 3,788 3,788
Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost 2,890 3,034 2,698
Interest Cost 3,194 2,740 3,121
Expected Return on Plan Assets 3,415 2,508 2,063
Prior Service Cost Amortization 1,092 1,208 1,210
Actuarial Loss Amortization (1,020) (1,045) $ (744)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]     Other Nonoperating Income (Expense)
Sub-total 4,781 5,519 $ 5,710
Amounts Capitalized or Deferred 2,388 3,136 2,865
NPBC Recognized 2,393 2,383 2,845
Supplemental Employee Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service Cost 273 354 283
Interest Cost 472 458 549
Prior Service Cost Amortization 55 56 57
Actuarial Loss Amortization $ (794) $ (1,489) (1,036)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Other Nonoperating Income (Expense) Other Nonoperating Income (Expense)  
Sub-total $ 1,594 $ 2,357 1,925
Amounts Capitalized or Deferred 472 712 579
NPBC Recognized $ 1,122 $ 1,645 $ 1,346