PROPERTY, PLANT AND EQUIPMENT - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 8,554,789	$ 9,161,704
Accumulated depreciation	(4,800,583)	(4,659,620)
Property, plant and equipment, net	3,754,206	4,502,084
Contract drilling services equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,330,464	7,881,323
Contract drilling services equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	4 years
Contract drilling services equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Tubulars
Property, Plant and Equipment [Line Items]
Estimated useful lives	4 years
Property, plant and equipment, gross	$ 616,460	618,310
Real estate properties
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 72,525	72,507
Real estate properties | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Real estate properties | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	45 years
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 465,278	471,803
Other | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Other | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	23 years
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 70,062	$ 117,761