Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - Commodity Contract - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	$ (286)	$ (515)
Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	8	1
Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	0	3
Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(284)	(490)
Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(10)	(29)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	1,332	(1,484)
Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	1,772	341
Not Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	156	2
Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(568)	(1,764)
Not Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	$ (28)	$ (63)