LEASES - Cost and Accumulated Depreciation (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
Property and equipment, at cost	$ 3,015,669	$ 2,906,648
Less: accumulated depreciation	(1,484,050)	(1,408,601)
Property and equipment, net	1,531,619	1,498,047
Mohegan Sun
Lessee, Lease, Description [Line Items]
Property and equipment, at cost	491,673	484,143
Less: accumulated depreciation	(218,873)	(198,080)
Property and equipment, net	$ 272,800	$ 286,063