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Long-Term Debt and Capital Lease Obligations - Additional Information (Detail) (USD $) | 0 Months Ended | 12 Months Ended
--- | --- | ---
Oct. 29, 2014 | Dec. 31, 2014
Line of Credit Facility [Line Items] |  |
Line of Credit facility, maturity date | Oct. 29, 2019 |
Line of Credit facility, estimated increase in borrowings |  | $ 1,800,000,000 md_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity
Line of credit description |  | At the Company’s option, borrowings under the Credit Agreement (other than swingline loans) will bear interest at (i) the Alternate Base Rate (defined as the higher of (a) the prime rate, (b) the Federal Funds Rate plus 1/2 of 1.00% and (c) LIBOR for an interest period of one month plus 1.00%) plus an applicable margin rate ranging from 0.125% to 0.750% based on the Company’s consolidated leverage ratio or (ii) the LIBOR rate plus an applicable margin rate ranging from 1.125% to 1.750% based on the Company’s consolidated leverage ratio. Swingline loans will bear interest at the alternate base rate plus the applicable margin.
Line of Credit facility, reduction in the available balance |  | 200,000 md_LineOfCreditFacilityReductionInAvailableBalance
Line of Credit facility, available balance |  | 931,800,000 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Minimum [Member] |  |
Line of Credit Facility [Line Items] |  |
Commitment fee percentage | 0.15%us-gaap_LineOfCreditFacilityCommitmentFeePercentage / us-gaap_RangeAxis = us-gaap_MinimumMember |
Maximum [Member] |  |
Line of Credit Facility [Line Items] |  |
Commitment fee percentage | 0.30%us-gaap_LineOfCreditFacilityCommitmentFeePercentage / us-gaap_RangeAxis = us-gaap_MaximumMember |
Alternate Base Rate [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt instrument, interest rate |  | 1/2 of 1.00%
Alternate Base Rate [Member] | LIBOR [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt instrument, interest rate |  | LIBOR for an interest period of one month plus 1.00%
Debt instrument, variable interest rate | 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = md_AlternateBaseRateMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember |
Applicable Margin Rate [Member] | LIBOR [Member] | Minimum [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt instrument, variable interest rate | 0.125%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = md_ApplicableMarginRateMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember |
Applicable Margin Rate [Member] | LIBOR [Member] | Maximum [Member] |  |
Line of Credit Facility [Line Items] |  |
Debt instrument, variable interest rate | 0.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = md_ApplicableMarginRateMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember |
Unsecured Revolving Credit Facility [Member] |  |
Line of Credit Facility [Line Items] |  |
Line of Credit facility, borrowing capacity | 1,300,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = md_UnsecuredRevolvingCreditFacilityMember |
Term Loan Credit Facility [Member] |  |
Line of Credit Facility [Line Items] |  |
Line of Credit facility, borrowing capacity | 200,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = md_TermLoanCreditFacilityMember |
Swingline Loans [Member] |  |
Line of Credit Facility [Line Items] |  |
Line of Credit facility, borrowing capacity | 75,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = md_SwingLineLoansMember |
Letter of Credit [Member] |  |
Line of Credit Facility [Line Items] |  |
Line of Credit facility, borrowing capacity | 37,500,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = us-gaap_LetterOfCreditMember |

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- Definition Line of credit facility potential increase in borrowing capacity. + References No definition available. + Details
Name: | md_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity
Namespace Prefix: | md_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line of credit facility, reduction in the available balance + References No definition available. + Details
Name: | md_LineOfCreditFacilityReductionInAvailableBalance
Namespace Prefix: | md_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used. + References No definition available. + Details
Name: | us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Description of the terms of a credit facility arrangement. Terms typically include interest rate, collateral required, guarantees required, repayment requirements, and restrictions on use of assets and activities of the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityDescription
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | us-gaap_CreditFacilityAxis=md_TermLoanCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=md_UnsecuredRevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=md_AlternateBaseRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=md_ApplicableMarginRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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