LONG-TERM DEBT - Additional Information (Details) - USD ($)					1 Months Ended				3 Months Ended			9 Months Ended		12 Months Ended
	Nov. 13, 2019	Jan. 17, 2019	Apr. 17, 2015	Feb. 10, 2014	Dec. 19, 2018	Jun. 30, 2017	Apr. 18, 2017	Apr. 21, 2016	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Jun. 25, 2020	Dec. 31, 2019	Feb. 28, 2019	Dec. 20, 2018	Feb. 15, 2014
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage											9.25%			9.25%
Debt Instrument, Interest Rate Terms							During each of the nine month periods in September 30, 2020 and 2019, the Company repaid approximately $2.5 million under the 2017 Credit Facility.The 2017 Credit Facility contains 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 2022 Notes. The 2017 Credit Facility also contains 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 contains 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 also contains 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 and 6.75 to 1.00 in 2022.
Interest Expense, Total									$ 18,243,000	$ 20,239,000		$ 55,776,000	$ 61,647,000
Repayments of Long Term Debt, Excess Cash Flow Payments										3,500,000		11,100,000
Comcast Note [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount																	$ 11,900,000
Debt Instrument, Interest Rate, Stated Percentage																	10.47%
Senior Secured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 350,000,000						$ 350,000,000			$ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage									7.375%			7.375%
9.25% Senior Subordinated Notes due February 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage									9.25%			9.25%
Debt Instrument, Repurchase Amount											$ 243,000,000			$ 243,000,000
Debt Instrument, Redemption Price, Percentage											100.88%
9.25% Senior Subordinated Notes due February 2020 [Member] | Private Offering [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 335,000,000
Debt Instrument, Periodic Payment				$ 15,500,000
Senior Subordinated Notes due April 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Description			an original issue price of 100.0% plus accrued interest									The 2022 Notes were offered at an original issue price of 100.0% plus accrued interest from April 17, 2015, and will mature on April 15, 2022.
MGM National Harbor Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 50,000,000			$ 50,000,000						$ 50,000,000
Long-term Debt, Gross									$ 57,300,000			$ 57,300,000
Debt Instrument, Interest Rate, Stated Percentage									7.00%			7.00%
Debt Instrument, Unamortized Discount (Premium), Net									$ 1,000,000			$ 1,000,000
Long Term Debt Percentage Paid In Kind												4.00%
Debt Issuance Costs, Net									1,700,000			$ 1,700,000
ABL Facility
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 37,500,000
Letters of Credit									871,000			871,000
Line of Credit Facility, Maximum Borrowing Capacity	25,000,000							$ 25,000,000
Percentage Borrowing Of Eligible Accounts								(85.00%)
ABL Amendment
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 37,500,000
Period prior to the earlier to occur of the term loan maturity or stated maturity	30 days
Revolving Loan
Debt Instrument [Line Items]
Letters of Credit	$ 7,500,000
Letter of Credit Facility
Debt Instrument [Line Items]
Borrowings outstanding									27,500,000			$ 27,500,000
2017 Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 350,000,000
Covenant Compliance Description For Maintaining Interest Coverage Ratio												maintaining an interest coverage ratio of no less than:1.25 to 1.00 on June 30, 2017 and the last day of each fiscal quarter thereafter.
Covenant Compliance Description For Maintaining Total Leverage Ratio												maintaining a senior leverage ratio of no greater than:5.85 to 1.00 on June 30, 2017 and the last day of each fiscal quarter thereafter.
Repayments of Long-term Debt, Total					$ 20,000,000				824,000	824,000
Percentage of Outstanding Principal Amount						0.25%
Long-term Debt, Gross							$ 350,000,000		318,200,000			$ 318,200,000				$ 320,600,000
Debt Instrument, Interest Rate, Stated Percentage							2.00%
Debt Instrument, Description							The 2017 Credit Facility matures 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 2022 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 5.23% for 2020 and was 6.41% for 2019.
2018 Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount															$ 3,600,000			$ 192,000,000
Number of Days to Notify the Changes														5 days
Debt Instrument, Interest Rate, Stated Percentage, If 50% of Term Repaid														11.875%
Debt Instrument, Interest Rate, Stated Percentage, If 75% of Term Repaid														10.875%
Excess Cash Flows														75.00%
Percentage of Distributions														100.00%
Repayments of Long-term Debt, Total									12,100,000	7,100,000		32,400,000	21,300,000
Long-term Debt, Gross									134,700,000			$ 134,700,000				$ 167,100,000
Debt Instrument, Interest Rate, Stated Percentage											12.875%			12.875%
Debt Instrument, Interest Rate Terms												Borrowings under the 2018 Credit Facility are 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 satisfy 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 notifies the Company within five (5) business days prior to funding the borrowings under the 2018 Credit Facility that it disagrees with such determination (including a reasonable description of the basis upon which it disagrees).
Interest Expense, Total									1,100,000	$ 986,000		$ 3,200,000	$ 2,900,000
Debt Instrument Additional Interest Payment Term On Prepayment												The term loans could have been voluntarily prepaid prior to February 15, 2020 subject to payment of a prepayment premium. The Company is 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 is also required to use 75% of excess cash flow ("ECF payment") as defined in the 2018 Credit Facility, which exclude 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.
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, Net									$ 875,000			$ 875,000
Senior Subordinated Notes Due From 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.375%	100.00%															9.25%
Debt Instrument, Redemption Price, Percentage		100.00%