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Commitments and Contingencies (Narrative) (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Other Income And Other Expense Disclosure [Line Items] |  |  |
Rent expense | $ 23.9 | $ 20.8 | $ 19.8

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- Details
Name: | md_OtherIncomeAndOtherExpenseDisclosureLineItems
Namespace Prefix: | md_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Rental expense incurred for leased assets including furniture and equipment which has not been recognized in costs and expenses applicable to sales and revenues; for example, cost of goods sold or other operating costs and expenses. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration