Employee Benefit Plans: Plan Contributions (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Estimated Future Employer Contributions in Next Fiscal Year	$ 0
Payment for Pension Benefits	0
Estimated Future Employer Contributions in Current Fiscal Year	0
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated Future Employer Contributions in Next Fiscal Year	4,808
Payment for Pension Benefits	3,690
Estimated Future Employer Contributions in Current Fiscal Year	1,230
Supplemental Non-Qualified Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Estimated Future Employer Contributions in Next Fiscal Year	2,417
Payment for Pension Benefits	1,673
Estimated Future Employer Contributions in Current Fiscal Year	$ 558