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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 |

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