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Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | $ 3,393 | $ 3,295 | $ 3,402
Interest Cost | 5,878 | 6,057 | 5,945
Expected Return on Plan Assets | (7,785) | (7,306) | (7,257)
Prior Service Cost Amortization | 324 | 263 | 263
Actuarial Loss Amortization | 5,786 | 4,662 | 4,398
Sub-total | 7,596 | 6,971 | 6,751
Amounts Capitalized or Deferred | (3,465) | (3,122) | (3,008)
NPBC Recognized | 4,131 | 3,849 | 3,743
Other Postretirement Benefit Plans, Defined Benefit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 2,933 | 2,974 | 2,610
Interest Cost | 3,404 | 3,913 | 3,232
Expected Return on Plan Assets | (1,635) | (1,347) | (1,205)
Prior Service Cost Amortization | 1,309 | 1,399 | 1,486
Actuarial Loss Amortization | 1,383 | 2,098 | 1,049
Sub-total | 7,394 | 9,037 | 7,172
Amounts Capitalized or Deferred | (3,416) | (4,515) | (3,351)
NPBC Recognized | 3,978 | 4,522 | 3,821
Supplemental Employee Retirement Plans, Defined Benefit |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 487 | 460 | 162
Interest Cost | 404 | 392 | 386
Prior Service Cost Amortization | 189 | 189 | 189
Actuarial Loss Amortization | 486 | 295 | 375
Sub-total | 1,566 | 1,336 | 1,112
Amounts Capitalized or Deferred | (451) | (397) | (290)
NPBC Recognized | $ 1,115 | $ 939 | $ 822

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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