Subsequent Event - Additional Information (Detail) - New Credit Agreement [Member] - Subsequent Event [Member]	Oct. 30, 2017 USD ($)
Subsequent Event [Line Items]
Line of Credit facility, maturity date	Oct. 31, 2022
Minimum [Member]
Subsequent Event [Line Items]
Commitment fee percentage	0.15%
Maximum [Member]
Subsequent Event [Line Items]
Commitment fee percentage	0.30%
Alternate Base Rate [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Debt instrument, applicable margin rate	0.125%
Alternate Base Rate [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Debt instrument, applicable margin rate	0.75%
Alternate Base Rate [Member] \| Federal Funds Rate [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate	Federal Funds Rate plus 1/2 of 1.00%
Debt instrument, variable interest rate	1.00%
Alternate Base Rate [Member] \| LIBOR [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate	LIBOR for an interest period of one month plus 1.00%) plus an applicable margin rate ranging from 0.125% to 0.750%
Debt instrument, variable interest rate	1.00%
Applicable Margin Rate [Member] \| LIBOR [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Debt instrument, variable interest rate	1.125%
Applicable Margin Rate [Member] \| LIBOR [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Debt instrument, variable interest rate	1.75%
Unsecured Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Line of Credit facility, borrowing capacity	$ 2,000,000,000
Letters of Credit [Member]
Subsequent Event [Line Items]
Line of Credit facility, borrowing capacity	$ 37,500,000

Debt instrument additional basis spread.

No definition available.

Name:	md_DebtInstrumentAdditionalBasisSpread
Namespace Prefix:	md_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

- 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

- 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

- 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

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=md_NewCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_FederalFundsEffectiveSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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