REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2019 USD ($) month	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Revenue From Contract With Customer [Line Items]
Contract drilling services	$ 2,785,557	$ 2,474,458	$ 1,792,476
Capitalized fulfillment costs	$ 13,900
Period of unsatisfied performance obligations represented in backlog contracts with month-to-month terms | month	1
Accounts receivable payment period	30 days
Contract Drilling - Early Termination
Revenue From Contract With Customer [Line Items]
Contract drilling services	$ 11,300	$ 17,100	$ 29,400