SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - IMPACT OF ASC 740 ON THE UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization	$ 111,387	$ 107,368	$ 81,109
Deferred income taxes	$ 23,796	34,346	(2,822)
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization		119,894	91,730
Deferred income taxes		(9,092)	(59,013)
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization		(12,526)	(10,621)
Deferred income taxes		$ 43,438	$ 56,191