REVENUE - TIMING OF REVENUE RECOGNITION (Details) $ in Thousands	12 Months Ended
	Sep. 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	(66,227)
Increase (decrease) for unbilled revenue	(689)
Increase (decrease) for customers' credits	(209)
Billed, end	139,263
Unbilled, end	6,510
Customers' credit, end	$ 27,116