Accounting for Derivative Instruments and Hedging Activities Contractual Contingent Liability (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	$ 29,464	$ 42,885
Posted Collateral	11,990	20,903
Additional Collateral, Aggregate Fair Value	21,991	26,966
Natural Gas Portfolio [Member]
Derivative [Line Items]
Posted Collateral	12,000
Credit Rating [Member]
Derivative [Line Items]
Posted Collateral	3,200
Credit Rating [Member] \| Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	21,991	26,966
Posted Collateral	0	0
Additional Collateral, Aggregate Fair Value	21,991	26,966
Credit Rating [Member] \| Natural Gas Portfolio [Member]
Derivative [Line Items]
Posted Collateral	1,000
Requested Credit for Adequate Assurance [Member] \| Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	7,330	6,576
Posted Collateral	0	0
Additional Collateral, Aggregate Fair Value	0	0
Forward Value of Contract [Member] \| Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	143	9,343
Posted Collateral	$ 11,990	$ 20,903

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624258-113959

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- Definition

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624258-113959

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- Definition

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

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624258-113959

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