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Long-Term Debt and Capital Lease Obligations - Schedule of Long-Term Debt (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Long-term debt $ 568,000us-gaap_LongTermDebt $ 27,000us-gaap_LongTermDebt
Less: Current portion (10,000)us-gaap_LongTermDebtCurrent  
Long-term portion 558,000us-gaap_LongTermDebtNoncurrent 27,000us-gaap_LongTermDebtNoncurrent
Term Loan Credit Facility [Member]    
Debt Instrument [Line Items]    
Long-term debt 200,000us-gaap_OtherLongTermDebt
/ us-gaap_CreditFacilityAxis
= md_TermLoanCreditFacilityMember
 
Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Long-term debt $ 368,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
$ 27,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember