REVENUE - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Contract costs and recognized income not yet billed, net of progress payments	$ 86,260	$ 84,426
Increase (decrease) in contract assets balance	1,834
Contract costs and recognized income not yet billed, noncurrent	8,100	7,500
Contract liabilities	25,237	$ 24,386
Increase (decrease) in contract liabilities	$ 851