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Employee Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Net Periodic Benefit Cost (Income) | $ (1,651) | $ (1,566) | $ (3,301) | $ (3,132)
Pension Benefits (Pension Plan) |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service Cost | 971 | 924 | 1,943 | 1,849
Interest Cost | 4,297 | 4,109 | 8,594 | 8,218
Expected Return on Assets | (6,379) | (6,478) | (12,759) | (12,957)
Amortization of Prior Service Cost | 0 | 0 | 0 | 0
Amortization of Net Actuarial Loss | 39 | 0 | 79 | 0
Net Periodic Benefit Cost (Income) | (1,072) | (1,445) | (2,143) | (2,890)
Pension Benefits (ESSRP) |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service Cost | 0 | 18 | 0 | 36
Interest Cost | 474 | 473 | 948 | 945
Expected Return on Assets | 0 | 0 | 0 | 0
Amortization of Prior Service Cost | 0 | 0 | 0 | 0
Amortization of Net Actuarial Loss | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | 474 | 491 | 948 | 981
Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service Cost | 122 | 153 | 245 | 306
Interest Cost | 400 | 669 | 800 | 1,338
Expected Return on Assets | 0 | 0 | 0 | 0
Amortization of Prior Service Cost | (1,575) | (1,434) | (3,151) | (2,867)
Amortization of Net Actuarial Loss | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | $ (1,053) | $ (612) | $ (2,106) | $ (1,223)

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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 -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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