Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Derivative [Line Items]
Regulatory assets	$ 272,229		$ 271,344
Gas price derivatives
Derivative [Line Items]
Regulatory assets	1,302		$ 3,328
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	2,128	$ 25
Not Designated as Hedging Instrument | Cost of Sales | Electricity
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	1,362	0
Not Designated as Hedging Instrument | Cost of Sales | Natural Gas, Distribution
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 766	$ 25