LONG-TERM DEBT - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Debt Schedule [Abstract]
Long-term debt	$ 1,960,018	$ 1,909,157
Less: current portion of long-term debt	(74,266)	(76,909)
Long-term debt, net of current portion	1,885,752	1,832,248
Line of Credit | Senior Secured Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	137,000	102,000
Debt issuance costs	1,111	1,191
Line of Credit | Senior Secured Credit Facility - Term Loan A
Debt Schedule [Abstract]
Long-term debt	253,272	263,829
Debt issuance costs	3,668	4,236
Line of Credit | Senior Secured Credit Facility - Term Loan B
Debt Schedule [Abstract]
Long-term debt	804,174	805,394
Debt issuance costs	15,975	16,925
Line of Credit | 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Long-term debt	490,821	490,435
Line of Credit | Line of Credit
Debt Schedule [Abstract]
Long-term debt	75	0
Line of Credit | MGE Niagara Resorts Credit Facility - Revolving
Debt Schedule [Abstract]
Long-term debt	30,728	0
Line of Credit | MGE Niagara Credit Facility - Term Loan
Debt Schedule [Abstract]
Long-term debt	73,936	73,564
Debt issuance costs	963	1,002
Line of Credit | Mohegan Expo Credit Facility
Debt Schedule [Abstract]
Long-term debt	28,831	29,357
Debt issuance costs	827	925
Line of Credit | Guaranteed Credit Facility
Debt Schedule [Abstract]
Long-term debt	31,264	31,840
Convertible Debenture | MGE Niagara Convertible Debentures
Debt Schedule [Abstract]
Long-term debt	30,728	30,204
Note payable to banks | Redemption Note Payable
Debt Schedule [Abstract]
Long-term debt	78,035	81,329
Debt issuance costs	$ 22,072	23,905
Senior Unsecured Notes | 2016 7 7/8% Senior Unsecured Notes
Debt Schedule [Abstract]
Note stated interest rate	7.875%
Debt issuance costs	$ 9,179	9,565
Senior Unsecured Notes | Other
Debt Schedule [Abstract]
Long-term debt	$ 1,154	$ 1,205