PROPERTY, PLANT AND EQUIPMENT - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,368,606	$ 7,353,541
Accumulated depreciation	(4,346,271)	(4,226,254)
Property, plant and equipment, net	3,022,335	3,127,287
Assets held-for-sale	57,373	71,453
Drilling services equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 6,284,174	6,229,011
Drilling services equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	4 years
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	$ 555,968	573,900
Real estate properties
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 44,916	43,302
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	$ 420,589	459,741
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	$ 62,959	$ 47,587