PROPERTY, PLANT AND EQUIPMENT - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 8,486,200	$ 9,161,704
Accumulated depreciation	(4,839,859)	(4,659,620)
Property, plant and equipment, net	3,646,341	4,502,084
Drilling services equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,313,234	7,881,323
Drilling services equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	4 years
Drilling services equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Tubulars
Property, Plant and Equipment [Line Items]
Estimated useful life	4 years
Property, plant and equipment, gross	$ 615,281	618,310
Real estate properties
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 43,389	72,507
Real estate properties | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Real estate properties | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	45 years
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 464,704	471,803
Other | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Other | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	23 years
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 49,592	$ 117,761