Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,037,572	$ 6,963,327	$ 6,626,989
Changes To Our Segment Performance Measure - Assets	0
Discontinued Operations, Held-for-sale
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	0	0	24,724
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	207,495	209,478	194,193
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,755,056	2,707,695	2,629,267
Changes To Our Segment Performance Measure - Assets	(186,000)
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,639,430	3,623,475	3,398,473
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	372,503	342,085	314,764
Changes To Our Segment Performance Measure - Assets	186,000
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 63,088	80,594	65,568
Recasting of Intercompany Capital Lease
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		0	0
Recasting of Intercompany Capital Lease | Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		(188,000)	(261,000)
Recasting of Intercompany Capital Lease | Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		$ 188,000	$ 261,000