DERIVATIVE FINANCIAL INSTRUMENTS: Derivative Instruments, Notional Amounts (Details) (Details) MWh in Thousands, MMBTU in Thousands	Dec. 31, 2019 MMBTU MWh	Dec. 31, 2018 MMBTU MWh
Electricity (MWh) \| Long
Derivative
Derivative, Nonmonetary Notional Amount \| MWh	91	52
Electricity (MWh) \| Short
Derivative
Derivative, Nonmonetary Notional Amount \| MWh	138	39
Natural Gas (MMBTU) \| Long
Derivative
Derivative, Nonmonetary Notional Amount \| MMBTU	14,053	7,514
Natural Gas (MMBTU) \| Short
Derivative
Derivative, Nonmonetary Notional Amount \| MMBTU	78	446

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=109980867&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=109980867&loc=SL5579245-113959

Name:	us-gaap_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant