SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Narrative (Details)	3 Months Ended
	Dec. 31, 2020 USD ($) greographical_area	Dec. 31, 2019 USD ($)	Oct. 01, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Nov. 13, 2018 USD ($)
Summary of Significant Accounting Policies [Line Items]
Other operating expenses	$ 1,362,000	$ 1,422,000
Drilling services operating expenses, excluding depreciation and amortization	198,689,000	399,329,000
Cash, cash equivalents, and short-term investments	523,800,000
Restricted cash	48,700,000	39,300,000		$ 48,900,000	$ 35,000,000.0
Restricted cash from initial capitalization of captive insurance company	2,000,000.0			2,000,000.0
Additional cash restricted at the election of management for potential insurance claims	43,400,000			43,100,000
Retained earnings	2,911,006,000			3,010,012,000
Underwriting expenses	500,000	8,500,000
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)	$ (1,800,000)	1,000,000.0
Revision of Prior Period, Reclassification, Adjustment [Member]
Summary of Significant Accounting Policies [Line Items]
Other operating expenses		(10,100,000)
Drilling services operating expenses, excluding depreciation and amortization		10,100,000
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)
Argentina
Summary of Significant Accounting Policies [Line Items]
Cash	23,800,000
Intercompany Eliminations
Summary of Significant Accounting Policies [Line Items]
Premium revenues and expenses	7,100,000	$ 7,700,000
Minimum
Summary of Significant Accounting Policies [Line Items]
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]
Insurance coverage deductibles range for claims which occur outside or inside the United States	$ 10,000,000
Acquisition of Drilling Technology Companies
Summary of Significant Accounting Policies [Line Items]
Restricted cash	$ 3,200,000			$ 3,600,000
International Locations | Operating Revenue | Geographic Concentration Risk
Summary of Significant Accounting Policies [Line Items]
Concentration percentage	4.40%	7.80%
International Locations | South America | Segment Operating Revenue | Geographic Concentration Risk | International Solutions
Summary of Significant Accounting Policies [Line Items]
Concentration percentage	18.10%	87.00%
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
2018 Credit Facility | Letters of Credit
Summary of Significant Accounting Policies [Line Items]
Maximum borrowing capacity						$ 75,000,000.0