DERIVATIVE FINANCIAL INSTRUMENTS: Derivative Instruments, Notional Amounts (Details) (Details) MWh in Thousands, MMBTU in Thousands	Dec. 31, 2020 MMBTU MWh	Dec. 31, 2019 MMBTU MWh
Electricity (MWh) \| Long
Derivative
Derivative, Nonmonetary Notional Amount \| MWh	74	91
Electricity (MWh) \| Short
Derivative
Derivative, Nonmonetary Notional Amount \| MWh	0	138
Natural Gas (MMBTU) \| Long
Derivative
Derivative, Nonmonetary Notional Amount \| MMBTU	7,923	14,053
Natural Gas (MMBTU) \| Short
Derivative
Derivative, Nonmonetary Notional Amount \| MMBTU	775	78

Nominal number of units used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

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Balance Type:	na
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