PROPERTY, PLANT AND EQUIPMENT - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 9,161,704	$ 9,146,247
Accumulated depreciation	(4,659,620)	(4,288,865)
Property, plant and equipment, net	4,502,084	4,857,382	$ 5,001,051
Contract drilling services equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,881,323	7,829,038
Contract drilling services equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	4 years
Contract 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	$ 618,310	613,043
Real estate properties
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 72,507	68,888
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	$ 471,803	471,310
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	$ 117,761	$ 163,968