Risk Management and Derivatives: Derivatives Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative [Line Items]
Derivative Instrument, Loss Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Expense	Interest Expense	Interest Expense	Interest Expense
Derivative Instrument, Gain Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Fuel, purchased power and cost of natural gas sold	Fuel, purchased power and cost of natural gas sold	Fuel, purchased power and cost of natural gas sold	Fuel, purchased power and cost of natural gas sold
Cash Flow Hedging \| Interest Rate Swap and Commodity Derivative
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 4,000
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	$ 3,004	$ 6,248	(808)	$ 9,034
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(669)	(381)	1,482	(1,782)
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest rate swaps
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	712	712	2,138	2,138
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	(712)	(712)	(2,138)	(2,138)
Cash Flow Hedging \| Designated as Hedging Instrument \| Commodity Contract
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	2,292	5,536	(2,946)	6,896
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 43	$ 331	$ 3,620	$ 356

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.

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)
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Indicates line item in statement of income or comprehensive income that includes gain from effective portion of derivative instrument reclassified from accumulated other comprehensive income (AOCI) into income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
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Indicates line item in statement of income or comprehensive income that includes loss from effective portion of derivative instrument reclassified from accumulated other comprehensive income (AOCI) into income.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The effective portion of gain reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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The effective portion of loss reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

+ References

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-SubTopic 10
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