REVENUE FROM CONTRACTS WITH CLIENTS - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Revenue from Contract with Customer [Abstract]
Contract Assets: Trade receivables	$ 77,618	$ 88,867
Contract Assets: Unbilled revenue	17,211	17,474
Contract liabilities: Client deposits	36,689	39,222
Contract liabilities: Deferred revenue	18,933	29,420
Allowance for doubtful, uncollected archive invoices	$ 10,220	$ 2,647
Percentage of revenue billed from unbilled revenue	86.00%
Percentage of contract liabilities recognized as revenue	80.00%