REVENUE - TIMING OF REVENUE RECOGNITION (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2020 USD ($)
Timing of Revenue Recognition [Roll Forward]
Billed, beginning	$ 139,263
Unbilled, beginning	6,510
Customers' credit, beginning	27,116
Increase (decrease) for accounts receivable, billed	3,796
Increase (decrease) for unbilled revenue	2,228
Increase (decrease) for customers' credits	(7,060)
Billed, end	143,059
Unbilled, end	8,738
Customers' credit, end	$ 20,056