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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=mgp_A5.625SeniorNotesDue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgp_A4.5SeniorNotesDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgp_A4.50SeniorNotesDue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=mgp_OperatingPartnershipSeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgp_A5.75seniornotesdue2027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Operating Partnership Senior Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Dec. 31, 2017	Sep. 30, 2016	Aug. 31, 2016	Apr. 30, 2016
$1,050 million 5.625% senior notes, due 2024
Debt Instrument [Line Items]
Aggregate principal amount	$ 1,050,000		$ 1,050,000
$500 million 4.50% senior notes, due 2026
Debt Instrument [Line Items]
Aggregate principal amount	500,000		500,000
$350 million 4.50% senior notes, due 2028
Debt Instrument [Line Items]
Aggregate principal amount	$ 350,000		$ 350,000
Operating Partnership Senior Notes \| $1,050 million 5.625% senior notes, due 2024
Debt Instrument [Line Items]
Aggregate principal amount						$ 1,050,000
Interest rate						5.625%
Debt instrument redemption price percentage	100.00%
Operating Partnership Senior Notes \| $500 million 4.50% senior notes, due 2026
Debt Instrument [Line Items]
Aggregate principal amount					$ 500,000
Interest rate					4.50%
Operating Partnership Senior Notes \| $350 million 4.50% senior notes, due 2028
Debt Instrument [Line Items]
Aggregate principal amount				$ 350,000
Interest rate		5.75%		4.50%
Operating Partnership Senior Notes \| $750 million 5.75% senior notes due 2027
Debt Instrument [Line Items]
Aggregate principal amount		$ 750,000