PROPERTY, PLANT AND EQUIPMENT - Impairments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019 USD ($) rig	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) rig	Jun. 30, 2018 USD ($)	Jun. 29, 2019 USD ($) rig	Sep. 30, 2018 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
Property, plant and equipment, net	$ 4,583,673		$ 4,583,673			$ 4,857,382
Asset impairment charge	224,327	$ 0	224,327	$ 0
Domestic FlexRig4 Asset Group
Impaired Long-Lived Assets Held and Used [Line Items]
Property, plant and equipment, net	$ 107,500		$ 107,500		$ 317,800
Number of drill rigs evaluated for impairment | rig	20		20		71
International FlexRig4 Asset Group
Impaired Long-Lived Assets Held and Used [Line Items]
Property, plant and equipment, net	$ 47,800		$ 47,800		$ 55,700
Number of drill rigs evaluated for impairment | rig	8		8		10
FlexRig4 Asset Group
Impaired Long-Lived Assets Held and Used [Line Items]
Property, plant and equipment, net					$ 235,300
U.S. Land
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge	$ 216,900
International Land
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge	$ 7,400