Employee Benefit Plans: Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plan
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Net (gain) loss	$ 0	$ 0
Total AOCI	0	0
Supplemental Non-qualified Defined Benefit Retirement Plans
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Net (gain) loss	391	707
Total AOCI	391	707
Non-pension Defined Benefit Postretirement Healthcare Plan
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Net (gain) loss	0	0
Total AOCI	$ 0	$ 0