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Pension and other post-employment benefits - Schedule of Amounts Recognized in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Pension benefits |  |
Actuarial losses (gains) |  |
Balance, January 1 | $ (6,902) | $ (671)
Additions to AOCI | (31,048) | (12,600)
Amortization in current period | 1,499 | 617
Recognition of settlement gain |  | 235
Reclassification to regulatory accounts | 15,425 | 5,517
Ending balance, December 31 | (21,026) | (6,902)
Past service losses (gains) |  |
Beginning balance, January 1 | (2,627) | (3,363)
Additions to AOCI | 0 | 0
Amortization in current period | 1,468 | 1,491
Recognition of settlement gain |  | 0
Reclassification to regulatory accounts | (755) | (755)
Ending balance, December 31 | (1,914) | (2,627)
OPEB |  |
Actuarial losses (gains) |  |
Balance, January 1 | (35,275) | (33,550)
Additions to AOCI | (16,958) | (23,797)
Amortization in current period | 3,499 | 2,554
Recognition of settlement gain |  | 0
Reclassification to regulatory accounts | 15,257 | 19,518
Ending balance, December 31 | (33,477) | (35,275)
Past service losses (gains) |  |
Beginning balance, January 1 | (1,337) | (2,190)
Additions to AOCI | 853 | 853
Amortization in current period | 0 | 0
Recognition of settlement gain |  | 0
Reclassification to regulatory accounts | 0 | 0
Ending balance, December 31 | $ (484) | $ (1,337)

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- Definition Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-14A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (j) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-11 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A + Details
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