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Risk Management and Derivatives: Derivatives Designated as Hedge Instruments (Details) - Cash Flow Hedging - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | $ (744) | $ (1,199)
Designated as Hedging Instrument |  |
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 886 | 970
Interest rate swaps | Designated as Hedging Instrument |  |
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 713 | 713
Commodity Contract | Designated as Hedging Instrument |  |
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 173 | 257
Interest Rate Swap and Commodity Derivative |  |
Derivative [Line Items] |  |
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | 900 |
Interest Expense | Interest rate swaps |  |
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | (713) | (713)
Fuel, purchased power and cost of natural gas sold | Commodity Contract |  |
Derivative [Line Items] |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | $ (31) | $ (486)

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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + Details
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- Definition The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4D -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624177-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959 + Details
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