BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contract with Customers (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Contract assets	$ 129,200	$ 53,200
Contract related liabilities	60,331	71,248
Mohegan Sun Pocono
Revenue from External Customer [Line Items]
Contract related liabilities	16,800	18,000
Outstanding gaming chips and slot tickets liability
Revenue from External Customer [Line Items]
Contract related liabilities	7,623	7,968
Loyalty points deferred revenue liability
Revenue from External Customer [Line Items]
Contract related liabilities	35,368	40,968
Patron advances and other liability
Revenue from External Customer [Line Items]
Contract related liabilities	$ 17,340	$ 22,312