Debt Instrument, Basis Spread On Variable Rate Upon Rating Upgrade

No definition available.

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Period Type:	duration

- Definition

Debt Instrument, Payment Terms, Percent Of Principal Due At Payment

+ References

No definition available.

+ Details

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Namespace Prefix:	mgp_
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- Definition

Line Of Credit Facility, Increase (Decrease) In Maximum Borrowing Capacity

+ References

No definition available.

+ Details

Name:	mgp_LineOfCreditFacilityIncreaseDecreaseInMaximumBorrowingCapacity
Namespace Prefix:	mgp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
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Data Type:	xbrli:stringItemType
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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

+ Details

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Balance Type:	credit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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Debt - Narrative (Details)			3 Months Ended		6 Months Ended
Debt - Narrative (Details)	Jun. 14, 2018 USD ($)	Mar. 23, 2018	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Repayments of long-term debt					$ 13,000,000	$ 25,125,000
Estimated fair value of long-term debt			$ 3,900,000,000		3,900,000,000		$ 4,100,000,000
Amortization of deferred financing costs			3,100,000	$ 2,800,000	6,100,000	$ 5,600,000
Term Loan \| Senior Secured Term Loan A Facility
Debt Instrument [Line Items]
Principal amount under term loan facility			470,000,000		470,000,000
Borrowing capacity under credit facility	$ 200,000,000
Percentage of the aggregate principal amount due at quarterly payment	0.00625
Repayments of long-term debt			$ 5,000,000		$ 5,000,000
Interest rate			4.34%		4.34%
Term Loan \| Senior Secured Term Loan A Facility \| LIBOR
Debt Instrument [Line Items]
Variable rate	2.25%
Term Loan \| Senior Secured Term Loan B Facility
Debt Instrument [Line Items]
Principal amount under term loan facility			$ 1,800,000,000.0		$ 1,800,000,000.0
Repayments of long-term debt			$ 13,000,000		$ 13,000,000
Interest rate			4.09%		4.09%
Term Loan \| Senior Secured Term Loan B Facility \| LIBOR
Debt Instrument [Line Items]
Variable rate		2.00%
Variable rate upon corporate rating upgrade by S&P or Moody's		1.75%
Revolving Credit Facility \| Senior Secured Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing capacity under credit facility	$ 1,350,000,000.00		$ 1,400,000,000.0		$ 1,400,000,000.0
Variable rate	1.75%
Increase to the revolving facility	$ 750,000,000