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Accounts receivable and allowance for doubtful accounts (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011 | Mar. 31, 2011
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Accounts receivable and allowance for doubtful accounts [Abstract] |  |  |
Receivables past due 90 days or more | $ 34.6 | $ 29.8 | $ 33.9
Allowance for doubtful accounts receivable | $ 12.2 | $ 12.4 | $ 16.4

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- Details
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Namespace Prefix: | mdu_
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- Definition For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Financing receivables that are equal to or greater than 90 days past due. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953401-111524 + Details
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Balance Type: | debit
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