SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Allowance for doubtful accounts [Roll Forward]
Balance, beginning of period	$ 2,377	$ 1,900
Amount of charge (benefit) to expense	(1,122)
Amount of charge (benefit) to expense		432
Deductions and adjustments	(672)	45
Balance, end of period	$ 583	$ 2,377