Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,689,932	$ 7,558,457
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	167,350	130,245
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,982,841	2,900,983
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,052,860	4,032,339
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	407,107	417,715
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 79,774	$ 77,175