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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2021 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 29, 2021 | Sep. 27, 2021 | Apr. 16, 2021 | Oct. 01, 2020 | Dec. 20, 2018 | Nov. 13, 2018
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Cash, cash equivalents, and short-term investments |  | $ 1,100,000,000 |  |  |  |  |  |  |  |
Foreign currency losses |  | 5,300,000 | $ 8,800,000 | $ 8,200,000 |  |  |  |  |  |
Restricted cash and cash equivalents |  | 19,200,000 | 48,900,000 |  |  |  |  |  |  |
Restricted cash and cash equivalents from initial capitalization of captive insurance company |  | 2,000,000 | 2,000,000 |  |  |  |  |  |  |
Additional cash and cash equivalents restricted at the election of management for potential insurance claims |  | 17,700,000 | 43,100,000 |  |  |  |  |  |  |
Reserves for excess and obsolete inventory |  | 29,300,000 | 36,500,000 |  |  |  |  |  |  |
Capitalized interest |  | 0 | 0 | 0 |  |  |  |  |  |
Drilling services |  | 1,210,800,000 | 1,761,714,000 | 2,785,557,000 |  |  |  |  |  |
Early termination revenue |  | 7,700,000 | 73,400,000 | 11,300,000 |  |  |  |  |  |
Retained earnings |  | 2,573,375,000 | 3,010,012,000 |  |  |  |  |  |  |
Underwriting expenses |  | 12,600,000 | 16,400,000 |  |  |  |  |  |  |
Casualty insurance premiums |  | 21,900,000 | 6,700,000 |  |  |  |  |  |  |
Premium revenues and expenses |  | 35,400,000 | 36,900,000 |  |  |  |  |  |  |
Stop-loss program, maximum amount of claim |  | 50,000 |  |  |  |  |  |  |  |
Stop-loss medical expenses |  | $ 12,000,000 | $ 8,000,000 |  |  |  |  |  |  |
Cumulative inflation rate before a country is considered highly inflationary |  | 100.00% |  |  |  |  |  |  |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Accounts receivable, allowance for credit loss |  |  |  |  |  |  |  | $ 1,600,000 |  |
Retained earnings |  |  |  |  |  |  |  | $ (1,300,000) |  |
Operating Revenues | Geographic Concentration Risk | International Locations |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Concentration percentage |  | 5.00% | 8.30% |  |  |  |  |  |  |
Segment Revenue | International Solutions | Geographic Concentration Risk | International Locations | South America |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Concentration percentage |  | 48.90% | 61.60% |  |  |  |  |  |  |
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 |  | 148,000,000 | $ 212,000,000 | $ 322,800,000 |  |  |  |  |  |
Acquisition of Drilling Technologies Companies |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Restricted cash and cash equivalents |  | 1,500,000 | $ 3,600,000 |  |  |  |  |  |  |
2018 Credit Facility |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  |  |  |  |  | $ 750,000,000
Borrowings outstanding |  | 0 |  |  |  |  |  |  |  |
Available borrowing capacity |  | $ 750,000,000 |  |  |  |  |  |  |  |
2018 Credit Facility, Due November 2025 |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  |  | $ 680,000,000 |  |  |
Unsecured Senior Notes due March 19, 2025 |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  | 4.65% |  |  | 4.65% |
Face amount of debt |  |  |  |  |  |  |  |  | $ 487,100,000 |
Unsecured Senior Notes due March 19, 2025 | Forecast |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Make-whole premium and accrued interest | $ 58,100,000 |  |  |  |  |  |  |  |  |
Write-off of unamortized discount and debt issuance costs | $ 3,700,000 |  |  |  |  |  |  |  |  |
Unsecured Senior Notes due September 29, 2031 |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  | 2.90% |  |  |  |  |
Face amount of debt |  |  |  |  | $ 550,000,000 |  |  |  |  |
Letters of Credit | 2018 Credit Facility |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  |  |  |  |  | $ 75,000,000

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