LONG-TERM DEBT - Senior Secured Credit Facilities (Details) $ in Millions	Apr. 12, 2018 USD ($)
Revolving Facility and Term Loan B Facility
Debt Instrument [Line Items]
Debt issuance costs	$ 9.9
Credit Facility \| Senior Secured Credit Facility - Term Loan A \| Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	100.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan A \| Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	312.50%
Credit Facility \| Senior Secured Credit Facility - Term Loan A \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	0.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan A \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	200.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan A \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	412.50%
Credit Facility \| Senior Secured Credit Facility - Term Loan B
Debt Instrument [Line Items]
Increase to maximum borrowing capacity	$ 80.0
Credit Facility \| Senior Secured Credit Facility - Term Loan B \| Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	300.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan B \| Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	337.50%
Credit Facility \| Senior Secured Credit Facility - Term Loan B \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan B \| Eurodollar Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	400.00%
Credit Facility \| Senior Secured Credit Facility - Term Loan B \| Eurodollar Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	437.50%
Credit Facility \| Senior Secured Credit Facility, Term Loan A and B
Debt Instrument [Line Items]
Debt issuance costs	$ 7.3
Revolving Facility
Debt Instrument [Line Items]
Debt issuance costs	$ 2.6

Line of Credit Facility, Increase To Maximum Borrowing Capacity

No definition available.

Name:	mtga_LineofCreditFacilityIncreaseToMaximumBorrowingCapacity
Namespace Prefix:	mtga_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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

Amount, before accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section S45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68176171&loc=SL68176184-208336

+ Details

Name:	us-gaap_DebtIssuanceCostsLineOfCreditArrangementsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=mtga_SeniorSecuredCreditFacilityTermLoanAMaturingOctober2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=mtga_SeniorSecuredCreditFacilityTermLoanBMaturingOctober2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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