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