PROPERTY, PLANT AND EQUIPMENT - Impairments (Details) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) item $ / shares	Sep. 30, 2018 USD ($) item	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)
Impairments
Property, plant and equipment, net	$ 4,857,382	$ 4,857,382	$ 5,144,733	$ 5,001,051
International FlexRig4 Asset Group
Impairments
Property, plant and equipment, net	$ 63,000	$ 63,000
Two conventional rigs asset group
Impairments
Number of asset groups potentially impaired | item	2	2
Number of asset groups evaluated | item	2	2
Impairment charge for asset held for use		$ 0
U.S. Land | Land Rigs
Impairments
Impairment charge for assets held for sale			$ 6,300
U.S. Land | Two conventional rigs asset group
Impairments
Property, plant and equipment, net	$ 9,000	$ 9,000
Percentage the fair values exceed the net book values		64.00%
U.S. Land | Decommissioned rigs
Impairments
Impairment charge for assets held for sale	5,700
Impairment charge for assets held for sale, net of tax	$ 4,200
Diluted earnings per share for impairment charge for assets held for sale (in dollars per share) | $ / shares	$ 0.04
International Land | Two conventional rigs asset group
Impairments
Property, plant and equipment, net	$ 15,200	$ 15,200
Percentage the fair values exceed the net book values		141.00%
International Land | Six conventional rigs asset group
Impairments
Property, plant and equipment, net	20,800	$ 20,800
Impairment charge for asset held for use	$ 1,400
Number of rigs held for sale | item	6	6
Net book value of certain rig components transferred	$ 8,500	$ 8,500
Impairment charge for assets held for sale	9,200
Impairment charge for assets held for sale, net of tax	$ 7,000
Diluted earnings per share for impairment charge for assets held for sale (in dollars per share) | $ / shares	$ 0.06
Impairment charge for asset held for use, net of tax	$ 1,000
Diluted earnings per share for impairment charge for assets held for use (in dollars per share) | $ / shares	$ 0.01