The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 130,200	$ 141,700	$ 258,500	$ 281,700
Abandonments included in depreciation	900	4,400	1,700	5,400
Gain on sale of assets	10,310	$ 11,546	14,589	$ 17,090
Property, plant and equipment, net	3,840,213		3,840,213		$ 4,502,084
Domestic And International Conventional, FlexRig3, And FlexRig4 Asset Groups
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	605,800		605,800
Tangible asset impairment charges	441,400		441,400
In-Process Drilling Equipment And Rotational Inventory
Property, Plant and Equipment [Line Items]
Tangible asset impairment charges			83,500
In-Process Drilling Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	68,400		68,400
Tangible asset impairment charges	44,900		44,900
Rotational Inventory
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	38,600		38,600
Tangible asset impairment charges	$ 38,600		38,600
U.S. Land \| Domestic And International Conventional, FlexRig3, And FlexRig4 Asset Groups
Property, Plant and Equipment [Line Items]
Tangible asset impairment charges			292,400
U.S. Land \| In-Process Drilling Equipment And Rotational Inventory
Property, Plant and Equipment [Line Items]
Tangible asset impairment charges			75,800
International Land \| Domestic And International Conventional, FlexRig3, And FlexRig4 Asset Groups
Property, Plant and Equipment [Line Items]
Tangible asset impairment charges			149,000
International Land \| In-Process Drilling Equipment And Rotational Inventory
Property, Plant and Equipment [Line Items]
Tangible asset impairment charges			$ 7,700