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v3.20.4

Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | $ 3,322 | $ 3,104 | $ 3,393
Interest Cost | 5,776 | 6,484 | 5,878
Expected Return on Plan Assets | (9,019) | (8,475) | (7,785)
Prior Service Cost Amortization | 320 | 320 | 324
Actuarial Loss Amortization | 6,472 | 4,324 | 5,786
Sub-total | 6,871 | 5,757 | 7,596
Amounts Capitalized or Deferred | (3,083) | (2,227) | (3,465)
NPBC Recognized | 3,788 | 3,530 | 4,131
Other Postretirement Benefit Plans, Defined Benefit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 2,698 | 2,304 | 2,933
Interest Cost | 3,121 | 3,426 | 3,404
Expected Return on Plan Assets | (2,063) | (1,645) | (1,635)
Prior Service Cost Amortization | 1,210 | 1,213 | 1,309
Actuarial Loss Amortization | 744 | 227 | 1,383
Sub-total | 5,710 | 5,525 | 7,394
Amounts Capitalized or Deferred | (2,865) | (2,317) | (3,416)
NPBC Recognized | 2,845 | 3,208 | 3,978
Supplemental Employee Retirement Plans, Defined Benefit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 283 | 247 | 487
Interest Cost | 549 | 567 | 404
Prior Service Cost Amortization | 57 | 56 | 189
Actuarial Loss Amortization | 1,036 | 628 | 486
Sub-total | 1,925 | 1,498 | 1,566
Amounts Capitalized or Deferred | (579) | (430) | (451)
NPBC Recognized | $ 1,346 | $ 1,068 | $ 1,115

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