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LONG-TERM DEBT - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Jan. 26, 2021	Sep. 30, 2020
Debt Schedule [Abstract]
Long-term debt	$ 1,942,942		$ 1,970,010
Less: current portion of long-term debt	(58,422)		(75,355)
Long-term debt, net of current portion	1,884,520		1,894,655
Credit Facility \| New Senior Secured Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	45,000		0
Credit Facility \| Prior Senior Secured Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	0		197,000
Credit Facility \| Prior Senior Secured Credit Facility - Term Loan A
Debt Schedule [Abstract]
Long-term debt	0		227,710
Debt issuance costs			4,199
Credit Facility \| Senior Secured Credit Facility - Term Loan B
Debt Schedule [Abstract]
Long-term debt	0		792,829
Debt issuance costs			20,809
Credit Facility \| MGE Niagara Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	28,231		26,187
Credit Facility \| MGE Niagara Credit Facility - Term Loan
Debt Schedule [Abstract]
Long-term debt	71,806		69,297
Debt issuance costs	788		847
Credit Facility \| Mohegan Expo Credit Facility
Debt Schedule [Abstract]
Long-term debt	26,211		27,750
Debt issuance costs	324		658
Credit Facility \| Guaranteed Credit Facility
Debt Schedule [Abstract]
Long-term debt	27,789		29,529
Debt issuance costs	649		877
Credit Facility \| Mohegan Tribe Subordinated Loan
Debt Schedule [Abstract]
Long-term debt	0		5,000
Senior Notes \| 2021 Senior Unsecured Notes
Debt Schedule [Abstract]
Long-term debt	1,156,911		0
Debt issuance costs	$ 18,089
Note stated interest rate	8.00%	8.00%
Senior Notes \| 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Long-term debt	$ 493,140		491,821
Debt issuance costs	$ 6,860		8,179
Note stated interest rate	7.875%
Convertible Debenture \| MGE Niagara Convertible Debenture
Debt Schedule [Abstract]
Long-term debt	$ 32,264		29,928
Note Payable to Banks \| Redemption Note Payable
Debt Schedule [Abstract]
Long-term debt	57,278		69,099
Debt issuance costs	10,302		15,701
Other \| Other
Debt Schedule [Abstract]
Long-term debt	$ 4,312		$ 3,860