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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Narrative (Details) MMBbls in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 USD ($) | Sep. 30, 2019 USD ($) | Sep. 30, 2018 USD ($) | Jul. 15, 2020 MMBbls | Jun. 30, 2020 MMBbls | Nov. 13, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Reduction in oil production | MMBbls |  |  |  | 7.7 | 9.7 |
Cash, cash equivalents, and short-term investments | $ 577,200,000 |  |  |  |  |
Foreign currency losses | 8,800,000 | $ 8,200,000 | $ 4,000,000.0 |  |  |
Restricted cash and cash equivalents | 48,900,000 | 35,000,000.0 |  |  |  |
Restricted cash and cash equivalents from initial capitalization of captive insurance company | 2,000,000.0 | 2,000,000 |  |  |  |
Additional cash and cash equivalents restricted at the election of management for potential insurance claims | 43,100,000 | 30,000,000.0 |  |  |  |
Reserves for excess and obsolete inventory | 36,500,000 | 11,500,000 |  |  |  |
Capitalized interest | 0 | 0 | 400,000 |  |  |
Drilling services | 1,761,714,000 | $ 2,785,557,000 | 2,474,458,000 |  |  |
Underwriting expenses | 16,400,000 |  |  |  |  |
Premium revenues and expenses | 36,900,000 |  |  |  |  |
Stop-loss program, maximum amount of claim | $ 50,000 |  |  |  |  |
Cumulative inflation rate before a country is considered highly inflationary | 100.00% |  |  |  |  |
Operating Revenues | Geographic Concentration Risk | International Locations |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Concentration percentage | 8.30% | 7.60% |  |  |  |
Segment Revenue | International Solutions Segment | Geographic Concentration Risk | International Locations | South America |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Concentration percentage | 61.60% | 91.60% |  |  |  |
Minimum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Estimated life of finite-lived intangible assets used for amortization | 5 years |  |  |  |  |
Lease term, lessor | 3 years |  |  |  |  |
Lease term, lessee | 1 year |  |  |  |  |
Deductible per occurrence | $ 1,000,000 |  |  |  |  |
Maximum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Estimated life of finite-lived intangible assets used for amortization | 20 years |  |  |  |  |
Lease term, lessor | 10 years |  |  |  |  |
Lease term, lessee | 15 years |  |  |  |  |
Deductible per occurrence | $ 10,000,000 |  |  |  |  |
Reimbursements Received for Out-of-Pocket Expenses |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Drilling services | 212,000,000.0 | $ 322,800,000 | 274,700,000 |  |  |
Contract Drilling - Early Termination |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Drilling services | 73,400,000 | 11,300,000 | $ 17,100,000 |  |  |
Acquisition of Drilling Technologies Companies |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Restricted cash and cash equivalents | 3,600,000 | $ 3,000,000.0 |  |  |  |
2018 Credit Facility |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  | $ 750,000,000.0
Borrowings outstanding | 0 |  |  |  |  |
Available borrowing capacity | $ 750,000,000.0 |  |  |  |  |
Letters of Credit | 2018 Credit Facility |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  | $ 75,000,000.0

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