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DERIVATIVE FINANCIAL INSTRUMENTS: Derivative Financial Instruments Level 3 (Tables) | 12 Months Ended
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Dec. 31, 2025
General Discussion of Derivative Instruments and Hedging Activities [Abstract] |
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance | The table below presents the gains and losses on derivatives not designated as hedging instruments for the years ended December 31 (in thousands of dollars):
|  | Location of Realized Gain/(Loss) on Derivatives Recognized in Income |  | Gain/(Loss) on Derivatives Recognized in Income(1)
|  |  | 2025 |  | 2024 |  | 2023
Financial swaps |  | Operating revenues |  | $ | 559 |  |  | $ | 5,189 |  |  | $ | 4,216 |
Financial swaps |  | Purchased power |  | (3,967) |  |  | (7,101) |  |  | (8,542) |
Financial swaps |  | Fuel expense |  | (37,659) |  |  | (63,380) |  |  | (16,209) |
Forward contracts |  | Operating revenues |  | 917 |  |  | 1,885 |  |  | 2,280 |
Forward contracts |  | Purchased power |  | (1,017) |  |  | (3,742) |  |  | (4,035) |
Forward contracts |  | Fuel expense |  | (1,457) |  |  | (2,510) |  |  | (866) |
(1) Excludes unrealized gains or losses on derivatives, which are recorded on the balance sheet as regulatory assets or regulatory liabilities.
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value | The table below presents the fair values and locations of derivative instruments not designated as hedging instruments recorded on the balance sheets and reconciles the gross amounts of derivatives recognized as assets and as liabilities to the net amounts presented in the balance sheets (in thousands of dollars):
|  |  |  | Asset Derivatives |  | Liability Derivatives
|  | Balance Sheet Location |  | Gross Fair Value |  | Amounts Offset |  | Net Assets |  | Gross Fair Value |  | Amounts Offset |  | Net Liabilities
December 31, 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial swaps |  | Other current liabilities |  | 2,535 |  |  | (2,535) |  |  | — |  |  | 34,486 |  |  | (29,394) |  | (1) | 5,092 |
Forward contracts |  | Other current assets |  | 3 |  |  | — |  |  | 3 |  |  | — |  |  | — |  |  | — |
Forward contracts |  | Other current liabilities |  | — |  |  | — |  |  | — |  |  | 1,009 |  |  | — |  |  | 1,009 |
Long-term: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial swaps |  | Other liabilities |  | 1,444 |  |  | (1,444) |  |  | — |  |  | 7,479 |  |  | (4,385) |  | (2) | 3,094 |
Forward contracts |  | Other liabilities |  | — |  |  | — |  |  | — |  |  | 10,524 |  |  | — |  |  | 10,524 |
Total |  |  |  | $ | 3,982 |  |  | $ | (3,979) |  |  | $ | 3 |  |  | $ | 53,498 |  |  | $ | (33,779) |  |  | $ | 19,719 |
December 31, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial swaps |  | Other current liabilities |  | 3,072 |  |  | (3,072) |  |  | — |  |  | 18,092 |  |  | (14,931) |  | (3) | 3,161 |
Forward contracts |  | Other current liabilities |  | — |  |  | — |  |  | — |  |  | 1,291 |  |  | — |  |  | 1,291 |
Long-term: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial swaps |  | Other assets |  | 1,939 |  |  | (1,939) |  | (4) | — |  |  | 409 |  |  | (409) |  |  | — |
Financial swaps |  | Other liabilities |  | 177 |  |  | (177) |  |  | — |  |  | 1,019 |  |  | (177) |  |  | 842 |
Forward contracts |  | Other liabilities |  | — |  |  | — |  |  | — |  |  | 10,965 |  |  | — |  |  | 10,965 |
Total |  |  |  | $ | 5,188 |  |  | $ | (5,188) |  |  | $ | — |  |  | $ | 31,776 |  |  | $ | (15,517) |  |  | $ | 16,259 |
(1) Current liability derivative amounts offset include $26.9 million of collateral receivable at December 31, 2025. (2) Long-term liability derivative amounts offset include $2.9 million of collateral receivable at December 31, 2025. (3) Current liability derivative amounts offset include $11.9 million of collateral receivable at December 31, 2024. (4) Long-term asset derivative amounts offset include $1.5 million of collateral payable at December 31, 2024.
Schedule of Derivative Instruments | The table below presents the volumes of derivative commodity forward contracts and swaps outstanding at December 31 (in thousands of units):
Commodity |  | Units |  | 2025 |  | 2024
Electricity purchases |  | MWh |  | 200 |  |  | 161 |
Electricity sales |  | MWh |  | 33 |  |  | 16 |
Natural gas purchases |  | MMBtu |  | 131,863 |  |  | 88,330 |

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- Definition Tabular disclosure of the location and amount of derivative instruments and nonderivative instruments designated as hedging instruments reported before netting adjustments, and the amount of gain (loss) on derivative instruments and nonderivative instruments designated and qualified as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4CC -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4CC Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4C -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4C Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4A -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4E + Details
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- Definition Tabular disclosure of pertinent information about a derivative or group of derivatives on a disaggregated basis, such as for individual instruments, or small groups of similar instruments. May include a combination of the type of instrument, risks being hedged, notional amount, hedge designation, related hedged item, inception date, maturity date, or other relevant item. + References No definition available. + Details
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