REVENUE - Contract Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2021	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Contract costs and recognized income not yet billed, net of progress payments	$ 74,341	$ 84,426
Increase (decrease) in contract assets balance	(10,085)
Contract costs and recognized income not yet billed, noncurrent	9,600	7,500
Contract liabilities	23,757	$ 24,386
Increase (decrease) in contract liabilities	$ (629)