SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Narrative (Details) bbl in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($) bbl	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) greographical_area bbl	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Nov. 13, 2018 USD ($)	Sep. 30, 2018 USD ($)
Summary of Significant Accounting Policies [Line Items]
Reduction in oil production | bbl	9.7		9.7
Cash, cash equivalents, and short-term investments	$ 492,000,000.0		$ 492,000,000.0
Cash and cash equivalents	426,245,000	$ 334,775,000	426,245,000	$ 334,775,000	$ 347,943,000		$ 284,355,000
Restricted cash	50,000,000.0	34,300,000	50,000,000.0	34,300,000	35,000,000.0		$ 41,800,000
Restricted cash from initial capitalization of captive insurance company	2,000,000.0		2,000,000.0		2,000,000
Additional cash restricted at the election of management for potential insurance claims	46,100,000		46,100,000		30,000,000.0
Restricted cash from other purposes	30,000.00		30,000.00
Underwriting expenses	1,100,000		15,800,000
Stop-loss program, maximum amount of claim			$ 50,000
Cumulative inflation rate before a country is considered highly inflationary (as a percent)			100.00%
Aggregate foreign currency gain (loss)	$ (3,200,000)	$ (100,000)	$ (6,000,000.0)	$ (4,600,000)
Minimum
Summary of Significant Accounting Policies [Line Items]
Rental contract period	1 year		1 year
Insurance coverage deductibles range for claims which occur outside or inside the United States			$ 1,000,000
Number of geographical areas operating in (more than) | greographical_area			1
Maximum
Summary of Significant Accounting Policies [Line Items]
Rental contract period	15 years		15 years
Insurance coverage deductibles range for claims which occur outside or inside the United States			$ 10,000,000
Intercompany Eliminations
Summary of Significant Accounting Policies [Line Items]
Premium revenues and expenses	$ 10,400,000		28,900,000
United States
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	376,100,000		376,100,000
International Locations
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 50,100,000		$ 50,100,000
International Locations | Operating Revenue | Geographic Concentration Risk
Summary of Significant Accounting Policies [Line Items]
Concentration percentage	7.30%	6.80%	7.90%	7.70%
Argentina
Summary of Significant Accounting Policies [Line Items]
Cash	$ 38,600,000		$ 38,600,000
International Solutions | South America | International Locations | Segment Operating Revenue | Geographic Concentration Risk
Summary of Significant Accounting Policies [Line Items]
Concentration percentage	33.20%	95.10%	68.20%	92.10%
Acquisition of Drilling Technology Companies
Summary of Significant Accounting Policies [Line Items]
Restricted cash	$ 1,900,000		$ 1,900,000		$ 3,000,000.0
2018 Credit Facility
Summary of Significant Accounting Policies [Line Items]
Maximum borrowing capacity						$ 750,000,000.0
Borrowings outstanding	0		0
Available borrowing capacity	$ 750,000,000.0		$ 750,000,000.0
2018 Credit Facility | Letters of Credit
Summary of Significant Accounting Policies [Line Items]
Maximum borrowing capacity						$ 75,000,000.0