REVENUE - TIMING OF REVENUE RECOGNITION (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2019 USD ($)
Timing of Revenue Recognition [Roll Forward]
Billed, beginning	$ 205,490
Unbilled, beginning	7,199
Customers' credit, beginning	27,325
Increase (decrease) for accounts receivable, billed	(30,820)
Increase (decrease) for unbilled revenue	214
Increase (decrease) for customers' credits	(7,832)
Billed, end	174,670
Unbilled, end	7,413
Customers' credit, end	$ 19,493