DERIVATIVE FINANCIAL INSTRUMENTS: Derivative Instruments, Notional Amounts (Details) (Details) MWh in Thousands, MMBTU in Thousands, Gallon in Thousands	Dec. 31, 2015 MWh MMBTU Gallon	Dec. 31, 2014 MWh MMBTU Gallon
Electricity [Member] | Long [Member]
Derivative
Derivative, Nonmonetary Notional Amount | MWh	357	115
Electricity [Member] | Short [Member]
Derivative
Derivative, Nonmonetary Notional Amount | MWh	120	238
Fuel [Member] | Long [Member]
Derivative
Derivative, Nonmonetary Notional Amount | MMBTU	11,597	6,913
Fuel [Member] | Short [Member]
Derivative
Derivative, Nonmonetary Notional Amount | MMBTU	78	409
Diesel Fuel [Member] | Long [Member]
Derivative
Derivative, Nonmonetary Notional Amount | Gallon	1,068	243