Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014	Dec. 31, 2014
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		$ 4,220,271			$ 3,934,925	$ 4,220,271		$ 3,934,925	$ 4,245,902
Impairment of Oil and Gas Properties						121,690		0
Non-cash impairment of our Oil and Gas equity investments		5,170			0	5,170		0
Corporate activities[Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		138,656			100,426	138,656		100,426	106,605
Electric Utilities [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	2,856,903			2,603,900	2,856,903		2,603,900	2,748,680
Gas Utilities [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		801,295			799,365	801,295		799,365	906,922
Power Generation [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	72,270			85,269	72,270		85,269	76,945
Coal Mining [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		76,079			73,701	76,079		73,701	74,407
Oil and Gas [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		275,068	[2],[3]		$ 272,264	275,068	[2],[3]	$ 272,264	$ 332,343
Impairment of Oil and Gas Properties		$ 94,000		$ 22,000		117,000
Non-cash impairment of our Oil and Gas equity investments						$ 5,170

[1] The PPA under which Black Hills Colorado IPP provides generation to support Colorado Electric customers from the Pueblo Airport Generation Station is accounted for as a capital lease. As such, assets owned by our Power Generation segment are recorded at Colorado Electric under accounting for a capital lease.

[2] As a result of continued low commodity prices during 2015, we recorded non-cash impairments of oil and gas assets included in our Oil and Gas segment of $94 million and $117 million for the for the three and six months ended June 30, 2015, respectively. See Note 16 to the Condensed Consolidated Financial statements in this Quarterly Report on Form 10-Q.

[3] Includes a noncash impairment of our Oil and Gas equity investments of $5.2 million for the three and six months ended June 30, 2015.