Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,829,050	$ 7,558,457
Corporate and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	108,418	130,245
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,040,064	2,900,983
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,201,325	4,032,339
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	403,491	417,715
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 75,752	$ 77,175