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COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands		1 Months Ended	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands	Apr. 28, 2015 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) ft²	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Purchase obligations
Purchase orders outstanding for drilling equipment			$ 56,200
Fiscal Year
2018			8,015
2019			5,454
2020			3,795
2021			2,944
2022			2,926
Thereafter			6,825
Total			29,959
Commitments and Contingencies
Total rent expense			14,000	$ 13,500	$ 13,600
CONTINGENCIES
Gain contingencies recognized in consolidated financial statements			$ 0
Judicial ruling \| Keel accident case
CONTINGENCIES
Legal settlement paid		$ 72,000
Judicial ruling \| Minimum \| Keel accident case
CONTINGENCIES
Damages value	$ 100,000
Operating lease
LEASES
Area of leased office space (in square feet) \| ft²			221,021