REVENUE - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract costs and recognized income not yet billed, net of progress payments	$ 94,495	$ 105,111
Decrease in contract assets balance	10,616
Contract costs and recognized income not yet billed, noncurrent	12,612	13,100
Reserves for contract risk	1,570
Contract liabilities	21,292
Increase (decrease) in contract liabilities	$ (4,967)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract costs and recognized income not yet billed, net of progress payments		105,111
Contract liabilities		$ 26,259