REVENUE - Contract Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 57,231		$ 82,545
Contract liabilities	(60,868)		(43,174)
Net contract asset (liability)	(3,637)		39,371
Revenue recognized related to contract liabilities	2,200	$ 39,400
Retention amounts included in accounts receivable	4,700		$ 4,200
Retained amount expected to be collected in the next twelve months	$ 4,400