REVENUE RECOGNITION - Changes in contract assets and liabilities (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2021 USD ($)
REVENUE RECOGNITION
Contract Assets: Unbilled receivables, beginning balance	$ 1,879
Contract Assets: Unbilled receivables, Additions	3,963
Contract Assets: Unbilled receivables, Deductions	(1,848)
Contract Assets: Unbilled receivables, ending balance	3,994
Contract Liabilities: Customer advances, beginning balance	11,392
Contract Liabilities: Customer advances, Additions	125,225
Contract Liabilities: Customer advances, Deductions	(116,648)
Contract Liabilities: Customer advances, ending balance	$ 19,969