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Subsequent events (Details) (USD $) | Oct. 04, 2012 Borrowing capacity amendment [Member] | Oct. 22, 2012 Refinancing of Debt [Member] MDU Energy Capital, LLC [Member] | May 15, 2013 Future issuance of debt [Member] MDU Energy Capital, LLC [Member]
--- | --- | --- | ---
Subsequent events [Line Items] |  |  |
Borrowing capacity of amended revolving credit agreement | $ 125,000,000 |  |
Issuance under agreement |  | 25,000,000 |
Weighted average interest rate |  | 4.10% |
Future issuance of debt |  |  | $ 25,000,000

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- Definition Borrowing capacity of amended revolving credit agreement. + References No definition available. + Details
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- Details
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