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Commitments And Contingencies: Future Purchase Agreement - Related Party (Details) - Wygen I Generating Facility - Purchase Option, Property
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
MW
Unrecorded Unconditional Purchase Obligation [Line Items]  
Number of Megawatts Capacity Purchased | MW 60
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration Dec. 31, 2022
Asset Purchase Option | $ $ 2.6
Property, Plant and Equipment, Useful Life 35 years