Risk Management Activities (Details) (USD $)	6 Months Ended				12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Derivative [Line Items]
Credit Exposure, Non-Investment Grade Company	$ 600,000
Derivative assets, current	903,000		16,595,000		3,236,000
Derivative assets, non-current	0		1,770,000		510,000
Derivative liabilities, current	69,270,000		85,675,000		96,541,000
Derivative liabilities, non-current	12,384,000		42,077,000		16,941,000
Cash Collateral included in other current assets or other liabilities	4,094,000		318,000		6,141,000
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative liabilities, current	6,965,000		6,766,000		7,039,000
Derivative liabilities, non-current	12,384,000		18,976,000		16,941,000
Accumulated Other Comprehensive Income (Loss) Pre Tax	(19,349,000)		(25,742,000)		(23,980,000)
Cash collateral receivable (payable) included in derivatives	0		0		0
Derivative, Remaining Maturity	3 years 6 months		4 years 6 months		4 years
Notional Amount, Interest Rate Derivatives	150,000,000	[1]	150,000,000	[1]	150,000,000	[1]
Weighted Average Fixed Interest Rate	5.04%		5.04%		5.04%
Pre-tax gain (loss) included in Consolidated Statement of Income	0		0		0
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	(7,000,000)
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative liabilities, current	61,899,000		78,001,000		88,148,000
Derivative liabilities, non-current	0		15,336,000		0
Accumulated Other Comprehensive Income (Loss) Pre Tax	0		0		0
Cash collateral receivable (payable) included in derivatives	5,960,000		6,160,000		5,960,000
Derivative, Remaining Maturity	0 years 6 months		1 year 6 months		1 year
Notional Amount, Interest Rate Derivatives	250,000,000	[2]	250,000,000	[2]	250,000,000	[2]
Weighted Average Fixed Interest Rate	5.67%		5.67%		5.67%
Pre-tax gain (loss) included in Consolidated Statement of Income	26,249,000		(3,507,000)		1,882,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Dedesignated Interest Rate Swap Expiring 2018 [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	5 years 6 months
Notional Amount, Interest Rate Derivatives	100,000,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Dedesignated Interest Rate Swaps Expiring 2028 [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	15 years 6 months
Notional Amount, Interest Rate Derivatives	150,000,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Credit Risk [Member]
Derivative [Line Items]
Notional Amount, Interest Rate Derivatives	50,000,000
Potential Future Exposure on Credit Related Contingent Feature	20,000,000
Black Hills Corporation [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount, Interest Rate Derivatives	75,000,000
Utilities Group [Member] | Natural Gas, Distribution [Member]
Derivative [Line Items]
Derivative assets, current	0		9,726,000		0
Derivative assets, non-current	0		199,000		43,000
Derivative liabilities, non-current	0		6,453,000		0
Cash collateral receivable (payable) included in derivatives	7,203,000		15,925,000		8,576,000
Cash Collateral included in other current assets or other liabilities	2,938,000		0		4,354,000
Net Unrealized (Gain) Loss Included in Regulatory Assets or Regulatory liabilities	8,450,000		13,691,000		9,596,000
Option Premium and commission included in Derivatives	1,247,000		1,238,000		1,063,000
Utilities Group [Member] | Future [Member] | Purchase Contract [Member] | Natural Gas, Distribution [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	13,330,000		12,440,000		15,350,000
Derivative, Remaining Maturity	77 months		78 months		83 months
Utilities Group [Member] | Commodity Option [Member] | Purchase Contract [Member] | Natural Gas, Distribution [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,850,000		2,840,000		2,430,000
Derivative, Remaining Maturity	5 months		9 months		2 months
Utilities Group [Member] | Basis Swap [Member] | Purchase Contract [Member] | Natural Gas, Distribution [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,650,000		7,270,000		12,020,000
Derivative, Remaining Maturity	66 months		78 months		72 months
Oil and Gas [Member]
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	700,000
Oil and Gas [Member] | Crude Oil [Member]
Derivative [Line Items]
Cash collateral receivable (payable) included in derivatives	(142,000)		613,000		786,000
Cash Collateral included in other current assets or other liabilities	(149,000)		267,000		1,078,000
Oil and Gas [Member] | Natural Gas [Member]
Derivative [Line Items]
Cash collateral receivable (payable) included in derivatives	(1,419,000)		553,000		620,000
Cash Collateral included in other current assets or other liabilities	(1,007,000)		51,000		709,000
Oil and Gas [Member] | Swaps, Options and Futures [Member] | Crude Oil [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	520,500	[3]	672,000	[3]	528,000	[3]
Maximum Length of Time Hedged in Cash Flow Hedge	0 years 6 months	[4]	1 year 6 months	[4]	1 year	[4]
Derivative assets, current	610,000		2,483,000		1,405,000
Derivative assets, non-current	0		1,316,000		297,000
Derivative liabilities, current	130,000		456,000		847,000
Derivative liabilities, non-current	0		981,000		0
Accumulated Other Comprehensive Income (Loss) Pre Tax	827,000		1,727,000		206,000
Oil and Gas [Member] | Swaps and Futures [Member] | Natural Gas [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,712,500	[3]	9,020,500	[3]	8,215,500	[3]
Maximum Length of Time Hedged in Cash Flow Hedge	0 years 1 month	[4]	1 year 3 months	[4]	0 years 9 months	[4]
Derivative assets, current	293,000		4,386,000		1,831,000
Derivative assets, non-current	0		255,000		170,000
Derivative liabilities, current	276,000		452,000		507,000
Derivative liabilities, non-current	0		331,000		0
Accumulated Other Comprehensive Income (Loss) Pre Tax	1,415,000		3,305,000		873,000
Power Generation [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount, Interest Rate Derivatives	$ 75,000,000

[1] These swaps have been designated to $75.0 million of borrowings on our Revolving Credit Facility and $75.0 million of borrowings on our project financing debt at Black Hills Wyoming. The swaps transferred to Black Hills Wyoming such that BHC and Black Hills Wyoming are both jointly and severally liable for the amount of those obligations. These swaps are priced using three-month LIBOR, matching the floating portion of the related swaps.

[2] Maximum terms in years reflect the amended early termination dates. If the early termination dates are not extended, the swaps will require cash settlement based on the swap value on the termination date. If extended, de-designated swaps totaling $100.0 million notional terminate in 5.5 years and de-designated swaps totaling $150.0 million notional terminate in 15.5 years.

[3] Crude oil in Bbls, natural gas in MMBtus.

[4] Refers to the term of the derivative instrument. Assets and liabilities are classified as current/non-current based on the term of the hedged transaction and the corresponding settlement of the derivative instrument.