REVENUE - TIMING OF REVENUE RECOGNITION (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Timing of Revenue Recognition [Roll Forward]
Billed, beginning	$ 212,838	$ 134,173
Unbilled, beginning	10,351	9,226
Customers' credit, beginning	32,586	25,934
Increase (decrease) for accounts receivable, billed	55,205	71,309
Increase (decrease) for unbilled revenue	4,681	3,437
Increase (decrease) for customers' credits	(10,370)	(3,235)
Billed, end	268,043	205,482
Unbilled, end	15,032	12,663
Customers' credit, end	$ 22,216	$ 22,699