Employee Benefit Plans: Amounts Recognized in the Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-current liability	$ (14,606)	$ (16,285)
Regulatory Liabilities	(163,216)	(148,855)
Defined Benefit Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset	19,099	18,998
Current liability	0	0
Non-current liability	(7,255)	(7,676)
Regulatory Liabilities	0	0
Supplemental Non-qualified Defined Benefit Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset	0	0
Current liability	(230)	(245)
Non-current liability	(2,762)	(3,173)
Regulatory Liabilities	0	0
Non-pension Defined Benefit Postretirement Healthcare Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset	0	0
Current liability	(466)	(534)
Non-current liability	(4,589)	(5,436)
Regulatory Liabilities	$ (2,441)	$ (1,758)