REVENUE FROM CONTRACTS WITH CUSTOMERS - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 2,367	$ 2,151
Change in contract liabilities balance:
Contract liabilities beginning balance	23,354	38,472
Payment received/accrued and deferred	19,312	30,863
Revenue recognized during the period	(34,030)	(45,981)
Contract liabilities ending balance	$ 8,636	$ 23,354