Common Stock Dividend Restrictions Subsidiaries (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Utilities Group [Member]
Restriction to Transfer Funds	No dividend is permitted if it would reduce the equity ratio of Black Hills Energy entities to below 40% of their total capitalization
Amount of Restricted Net Assets for Subsidiaries	$ 61.5
Non Regulated Energy Group [Member]
Amount of Restricted Net Assets for Subsidiaries	100.0
Restricted Cash and Cash Equivalents, Current	$ 9.3
Cheyenne Light [Member]
Debt Instrument, Covenant Description	Debt capitalization requirement of 0.60 to 1.00

Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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