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Risk Management and Derivatives: Derivatives Designated as Hedge Instruments (Details) - Cash Flow Hedging - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Derivative [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | $ (381) | $ (890) | $ (1,782) | $ (2,872)
Designated as Hedging Instrument |  |  |  |
Derivative [Line Items] |  |  |  |
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax | 6,248 | 1,403 | 9,034 | 3,097
Interest rate swaps | Interest Expense |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | (712) | (712) | (2,138) | (2,138)
Interest rate swaps | Designated as Hedging Instrument |  |  |  |
Derivative [Line Items] |  |  |  |
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax | 712 | 712 | 2,138 | 2,138
Commodity Contract | Fuel, purchased power and cost of natural gas sold |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 331 | (178) | 356 | (734)
Commodity Contract | Designated as Hedging Instrument |  |  |  |
Derivative [Line Items] |  |  |  |
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax | $ 5,536 | $ 691 | 6,896 | $ 959
Interest Rate Swap and Commodity Derivative |  |  |  |
Derivative [Line Items] |  |  |  |
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months |  |  | $ 4,000 |

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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=125515794&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=125515794&loc=SL5624171-113959 + Details
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- Definition Amount of unrealized gain (loss) arising from the change in fair value of price risk derivatives designated as cash flow hedging instruments recorded in accumulated other comprehensive income in the period, before taxes, to the extent that the cash flow hedge is determined to be effective. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959 + Details
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