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Accounts receivable and allowance for doubtful accounts | 9 Months Ended
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Sep. 30, 2011
Accounts receivable and allowance for doubtful accounts [Abstract] |
Accounts receivable and allowance for doubtful accounts |
3. | Accounts receivable and allowance for doubtful accounts
| Accounts receivable consists primarily of trade receivables from the sale of goods and services which are recorded at the invoiced amount net of allowance for doubtful accounts, and costs and estimated earnings in excess of billings on uncompleted contracts. The total balance of receivables past due 90 days or more was $27.9 million and $21.6 million as of September 30, 2011 and December 31, 2010, respectively.
| The allowance for doubtful accounts is determined through a review of past due balances and other specific account data. Account balances are written off when management determines the amounts to be uncollectible. The Company's allowance for doubtful accounts as of September 30, 2011 and 2010, and December 31, 2010, was $12.1 million, $15.9 million and $15.3 million, respectively.

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- Definition An element designated to encapsulate the entire schedule of any allowance and reserve accounts (their beginning and ending balances, as well as a reconciliation by type of activity during the period). Alternatively, disclosure of the required information may be within the footnotes to the financial statements or a supplemental schedule to the financial statements. Also, presents disclosure of balances of receivables past due 90 days or more. + Details
Name: | mdu_Accountsreceivableallowancefordoubtfulaccounts
Namespace Prefix: | mdu
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_ReceivablesAbstract
Namespace Prefix: | us-gaap
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration