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Common Stock Repurchase Programs - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2014 | Oct. 31, 2014 | Dec. 15, 2014 | Dec. 17, 2014
Common Stock [Line Items] |  |  |  |
Common stock paid | $ 488.4 us-gaap_StockRepurchaseProgramAuthorizedAmount1 | $ 600.0 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |  |
Common stock shares issued | 7.1 us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased |  |  |
Amount withheld to satisfy minimum statutory tax withholding obligations | 1.1 us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings |  |  |
JPMorgan Chase Bank, N.A [Member] |  |  |  |
Common Stock [Line Items] |  |  |  |
Common stock purchase |  |  | 200.0 us-gaap_AcceleratedShareRepurchasesSettlementPaymentOrReceipt / dei_LegalEntityAxis = md_JpMorganChaseBankMember |
Accelerated Share Repurchase (ASR) Agreements [Member] | JPMorgan Chase Bank, N.A [Member] |  |  |  |
Common Stock [Line Items] |  |  |  |
Common stock paid |  |  |  | $ 200.0 us-gaap_StockRepurchaseProgramAuthorizedAmount1 / dei_LegalEntityAxis = md_JpMorganChaseBankMember / us-gaap_ShareRepurchaseProgramAxis = md_AcceleratedShareRepurchaseAgreementsMember
Common stock shares issued |  |  |  | 2.5 us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased / dei_LegalEntityAxis = md_JpMorganChaseBankMember / us-gaap_ShareRepurchaseProgramAxis = md_AcceleratedShareRepurchaseAgreementsMember

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- Details
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Data Type: | xbrli:stringItemType
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- Definition Amount of cash receipt from (payment to) bank; or stock received from (issuance to) bank in the settlement of the accelerated share repurchase agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 25 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6405686&loc=d3e22802-112653 + Details
Name: | us-gaap_AcceleratedShareRepurchasesSettlementPaymentOrReceipt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The value of restricted shares issued as compensation, net of the value of shares for the payment of withholding taxes. This element is to be used only if shares are used in lieu of cash to satisfy all or a portion of withholding taxes. + References No definition available. + Details
Name: | us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
Name: | us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan. + References No definition available. + Details
Name: | us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Details
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- Details
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Data Type: | na
Balance Type: |
Period Type: |