LONG-TERM DEBT - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jan. 26, 2021	Sep. 30, 2020	Oct. 31, 2016
Debt Schedule [Abstract]
Long-term debt	$ 1,938,754		$ 1,970,010
Less: current portion of long-term debt	(80,276)		(75,355)
Long-term debt, net of current portion	1,858,478		1,894,655
Line of Credit
Debt Schedule [Abstract]
Long-term debt	20,227		0
Line of Credit | New Senior Secured Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	27,000		0
Line of Credit | Prior Senior Secured Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	0		197,000
Line of Credit | Prior Senior Secured Credit Facility - Term Loan A
Debt Schedule [Abstract]
Long-term debt	0		227,710
Debt issuance costs			4,199
Line of Credit | Senior Secured Credit Facility - Term Loan B
Debt Schedule [Abstract]
Long-term debt	$ 0		792,829
Debt issuance costs			20,809
Line of Credit | 2021 Senior Unsecured Notes
Debt Schedule [Abstract]
Interest rate, stated	8.00%
Debt issuance costs	$ 17,269
Line of Credit | 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Debt issuance costs	6,401		8,179
Line of Credit | MGE Niagara Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	27,534		26,187
Line of Credit | MGE Niagara Credit Facility - Swingline
Debt Schedule [Abstract]
Long-term debt	4,333		0
Line of Credit | MGE Niagara Credit Facility - Term Loan
Debt Schedule [Abstract]
Long-term debt	68,965		69,297
Debt issuance costs	855		847
Line of Credit | Mohegan Expo Credit Facility
Debt Schedule [Abstract]
Long-term debt	25,697		27,750
Debt issuance costs	214		658
Line of Credit | Guaranteed Credit Facility
Debt Schedule [Abstract]
Long-term debt	27,208		29,529
Debt issuance costs	573		877
Line of Credit | Mohegan Tribe Subordinated Loan
Debt Schedule [Abstract]
Long-term debt	0		5,000
Line of Credit | Redemption note payable
Debt Schedule [Abstract]
Debt issuance costs	8,710		15,701
Senior Notes | 2021 Senior Unsecured Notes
Debt Schedule [Abstract]
Long-term debt	1,157,731		0
Interest rate, stated		8.00%
Senior Notes | 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Long-term debt	493,599		491,821
Convertible Debenture | MGE Niagara Convertible Debenture
Debt Schedule [Abstract]
Long-term debt	31,468		29,928
Note Payable to Banks | Redemption note payable
Debt Schedule [Abstract]
Long-term debt	$ 53,130		69,099
Other | 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Interest rate, stated	7.875%			7.875%
Other | Other
Debt Schedule [Abstract]
Long-term debt	$ 1,862		$ 3,860