Accounting for Derivative Instruments and Hedging Activities - Contractual Contingent Liability (Details) - Electric derivative instruments - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Derivative [Line Items]
Fair Value Liability	$ 302,780	$ 329,553
Posted Collateral	52,260	77,969
Additional Collateral, Aggregate Fair Value	238,318	253,105
Credit rating2
Derivative [Line Items]
Fair Value Liability	238,318	253,105
Posted Collateral	0	0
Additional Collateral, Aggregate Fair Value	238,318	253,105
Requested credit for adequate assurance
Derivative [Line Items]
Fair Value Liability	20,833	21,927
Posted Collateral	0	0
Additional Collateral, Aggregate Fair Value	0	0
Forward value of contract3
Derivative [Line Items]
Fair Value Liability	43,629	54,521
Posted Collateral	$ 52,260	$ 77,969

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 185
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-URI https://asc.fasb.org/1943274/2147480401/815-10-55-185

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
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-Section 55
-Paragraph 185
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-185

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
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- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 185
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-185

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-Topic 815
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-Name Accounting Standards Codification
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-Paragraph 4H
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4H

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