LONG-TERM DEBT - Additional Information (Details)								1 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended
	Feb. 19, 2021 USD ($)	Jan. 08, 2021	Nov. 09, 2020 USD ($)	Nov. 13, 2019 USD ($)	Dec. 19, 2018 USD ($)	Apr. 18, 2017 USD ($)	Apr. 17, 2015 USD ($)	Apr. 18, 2017 USD ($)	Apr. 21, 2016 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jan. 07, 2021 USD ($)	Jun. 25, 2020 USD ($)	Dec. 31, 2018	Dec. 20, 2018 USD ($)
Debt Instrument [Line Items]
Deferred financing costs included in interest expense													$ 1,296,000	$ 2,128,000
Repayments of Long-term Debt, Total														20,300,000
Debt Instrument, Description						The 2017 Credit Facility contained customary representations and warranties and events of default, affirmative and negative covenants (in each case, subject to materiality exceptions and qualifications) which may be more restrictive than those governing the 7.375% Notes. The 2017 Credit Facility also contained certain financial covenants, including a maintenance covenant requiring the Company’s interest expense coverage ratio (defined as the ratio of consolidated EBITDA to consolidated interest expense) to be greater than or equal to 1.25 to 1.00 and its total senior secured leverage ratio (defined as the ratio of consolidated net senior secured indebtedness to consolidated EBITDA) to be less than or equal to 5.85 to 1.00.							The 2018 Credit Facility contained customary representations and warranties and events of default, affirmative and negative covenants (in each case, subject to materiality exceptions and qualifications). The 2018 Credit Facility, as amended, also contained certain financial covenants, including a maintenance covenant requiring the Company's total gross leverage ratio to be not greater than 8.0 to 1.00 in 2019, 7.5 to 1.00 in 2020, 7.25 to 1.00 in 2021, 6.75 to 1.00 in 2022 and 6.25 to 1.00 in 2023.
Gain Losses on Extinguishment of Debt										$ 0	$ 0		$ (6,949,000)	0	$ 2,900,000
Repayments of Long Term Debt, Excess Cash Flow Payments														3,800,000
Amortization of debt premium															3,500,000
Loss on retirement of debt													6,949,000	0
Senior Secured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							$ 350,000,000.0
Debt Instrument, Description							The 7.375% Notes were offered at an original issue price of 100.0% plus accrued interest from April 17, 2015 and matured on April 15, 2022
2028 Notes Offering
Debt Instrument [Line Items]
Face amount of debt																$ 825,000,000
Interest rate																7.375%
Percentage of issue price		100
Debt issuance costs										15,400,000			15,400,000
Deferred financing costs included in interest expense										471,000	1,100,000		1,300,000	2,100,000
Debt Issuance Costs, Net										15,400,000			15,400,000
Loss on retirement of debt													6,900,000
MGM National Harbor Loan [Member]
Debt Instrument [Line Items]
Face amount of debt										$ 50,000,000.0			$ 50,000,000.0						$ 50,000,000.0
Interest rate										7.00%			7.00%
Debt issuance costs										$ 1,700,000			$ 1,700,000
Long-term Debt, Gross															$ 57,900,000
Debt Instrument, Unamortized Discount (Premium), Net										1,000,000.0			$ 1,000,000.0
Long Term Debt Percentage Paid In Kind													4.00%
Debt Issuance Costs, Net										$ 1,700,000			$ 1,700,000
7.375% Senior Secured Notes due April 2022
Debt Instrument [Line Items]
Face amount of debt			$ 347,000,000
Interest rate										7.375%			7.375%
Percentage of exchange offer			99.15%
8.75% Senior Secured Notes due December 2022
Debt Instrument [Line Items]
Interest rate			8.75%							8.75%			8.75%		8.75%
Long-term Debt, Gross															$ 347,000,000.0
Debt Instrument, Redemption Price, Percentage													100.00%
Amount redeemable										$ 15,000,000			$ 15,000,000
ABL Facility
Debt Instrument [Line Items]
Face amount of debt				$ 37,500,000
Letters of Credit										871,000			$ 871,000
Line of Credit Facility, Maximum Borrowing Capacity	$ 50,000,000			37,500,000					$ 25,000,000
Letter of credit facility, maximum capacity	$ 5,000,000			$ 7,500,000
Percentage Borrowing Of Eligible Accounts	85.00%								(85.00%)
Period prior to the earlier to occur of the term loan maturity or stated maturity				30 days
Line of Credit Facility, Current Borrowing Capacity	$ 50,000,000
ABL Amendment
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 25,000,000
Letter of Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Description													Until its termination on settlement of the 2028 Notes, borrowings under the 2018 Credit Facility were subject to customary conditions precedent, as well as a requirement under the 2018 Credit Facility that (i) the Company's total gross leverage ratio on a pro forma basis be not greater than 8:00 to 1:00 (this total gross leverage ratio test steps down as described below), (ii) neither of the administrative agents under the Company's existing credit facilities nor the trustee under the Company's existing senior secured notes due 2022 have objected to the terms of the new credit documents and (iii) certification by the Company that the terms and conditions of the 2018 Credit Facility satisfied the requirements of the definition of “Permitted Refinancing” (as defined in the agreements governing the Company's existing credit facilities) and neither of the administrative agents under the Company's existing credit facilities notified the Company within five (5) business days prior to funding the borrowings under the 2018 Credit Facility that it disagreed with such determination (including a reasonable description of the basis upon which it disagrees).
2017 Credit Facility [Member]
Debt Instrument [Line Items]
Face amount of debt										$ 350,000,000.0			$ 350,000,000.0
Interest rate										8.75%			8.75%
Covenant Compliance Description For Maintaining Interest Coverage Ratio													maintaining an interest coverage ratio of no less than:
Covenant Compliance Description For Maintaining Total Leverage Ratio													maintaining a senior leverage ratio of no greater than:
Repayments of Long-term Debt, Total					$ 20,000,000.0						$ 824,000			$ 1,600,000
Long-term Debt, Gross						$ 350,000,000		$ 350,000,000
Debt Instrument, Description								Until its termination on settlement of the 2028 Notes, the 2017 Credit Facility matured on the earlier of (i) April 18, 2023, or (ii) in the event such debt is not repaid or refinanced, 91 days prior to the maturity of the Company’s 7.375% Notes (as defined below). At the Company’s election, the interest rate on borrowings under the 2017 Credit Facility are based on either (i) the then applicable base rate (as defined in the 2017 Credit Facility) as, for any day, a rate per annum (rounded upward, if necessary, to the next 1/100th of 1%) equal to the greater of (a) the prime rate published in the Wall Street Journal, (b) 1/2 of 1% in excess rate of the overnight Federal Funds Rate at any given time, (c) the one-month LIBOR rate commencing on such day plus 1.00%) and (d) 2%, or (ii) the then applicable LIBOR rate (as defined in the 2017 Credit Facility). The average interest rate was approximately 5.0% for 2021 and 5.62% for 2020.
2018 Credit Facility [Member]
Debt Instrument [Line Items]
Face amount of debt										$ 10,000,000			$ 10,000,000				$ 3,600,000		$ 192,000,000.0
Interest rate																		9.25%
Repayments of Long-term Debt, Total												$ 8,400,000
Long-term Debt, Gross															$ 129,900,000
Debt Instrument, Description													The 2018 Credit Facility was scheduled to mature on December 31, 2022 (the “Maturity Date”). In connection with the November 2020 Exchange Offer, we also entered into an amendment to certain terms of our 2018 Credit Facility including the extension of the maturity date to March 31, 2023. Interest rates on borrowings under the 2018 Credit Facility were either (i) from the Funding Date to the Maturity Date, 12.875% per annum, (ii) 11.875% per annum, once 50% of the term loan borrowings had been repaid or (iii) 10.875% per annum, once 75% of the term loan borrowings had been repaid. Interest payments began on the last day of the 3-month period commencing on the Funding Date. Within 90 days following the completion of the November 2020 Exchange Offer, the Company was required to repay $10 million of the 2018 Credit Facility. The amendment was accounted for as a modification in accordance with the provisions of ASC 470, “Debt”.
Debt Instrument Additional Interest Payment Term On Prepayment													The term loans could be voluntarily prepaid prior to February 15, 2020 subject to payment of a prepayment premium. The Company was required to repay principal to the extent then outstanding on each quarterly interest payment date, commencing on the last business day in March 2019, equal to one quarter of 7.5% of the aggregate initial principal amount of all term loans incurred on the Funding Date to December 2019, commencing on the last business day in March 2020, one quarter of 10.0% of the aggregate initial principal amount of all term loans incurred on the Funding Date to December 2021, and, commencing on the last business day in March 2021, one quarter of 12.5% of the aggregate initial principal amount of all term loans incurred on the Funding Date to December 2022. The Company was also required to use 75% of excess cash flow (“ECF payment”) as defined in the 2018 Credit Facility, which excluded any distributions to the Company or its restricted subsidiaries in respect of its interests in the MGM National Harbor, to repay outstanding term loans at par, paid semiannually and to use 100% of all distributions to the Company or its restricted subsidiaries received in respect of its interest in the MGM National Harbor to repay outstanding terms loans at par. During the three and six months ended June 30, 2020, the Company repaid approximately $8.4 million and $20.3 million, respectively under the 2018 Credit Facility. Included in the repayments made during the six months ended June 30, 2020 was approximately $3.8 million in ECF payments in accordance with the agreement.
Debt Instrument, Unamortized Discount (Premium), Net										3,800,000			$ 3,800,000
2018 Credit Facility [Member] | Debt Financing Cost [Member]
Debt Instrument [Line Items]
Debt issuance costs										875,000			875,000
Debt Issuance Costs, Net										$ 875,000			$ 875,000
Credit Facility 2017 And 2018 [Member] | 7.375% Senior Secured Notes due April 2022
Debt Instrument [Line Items]
Interest rate										7.375%			7.375%
Credit Facility 2017 And 2018 [Member] | 8.75% Senior Secured Notes due December 2022
Debt Instrument [Line Items]
Interest rate										8.75%			8.75%