REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenue From Contract With Customer [Line Items]
Drilling services	$ 1,761,714	$ 2,785,557	$ 2,474,458
Capitalized fulfillment costs	$ 6,200	13,900
Period of unsatisfied performance obligations represented in backlog contracts with month-to-month terms	1 month
Accounts receivable payment period	30 days
Contract Drilling - Early Termination
Revenue From Contract With Customer [Line Items]
Drilling services	$ 73,400	11,300	17,100
Notification Fee
Revenue From Contract With Customer [Line Items]
Drilling services	$ 2,900	$ 1,200	$ 200