SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - IMPACT OF ASC 740 ON THE UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization	$ 26,848	$ 27,516	$ 54,210	$ 52,153
Deferred income taxes			$ 20,909	34,975
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization		30,784		58,542
Deferred income taxes				318
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization		$ (3,268)		(6,389)
Deferred income taxes				$ 34,657