Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017
RESTRICTED CASH AND CASH EQUIVALENTS
Cash and cash equivalents	$ 243,912	$ 284,355	$ 334,764	$ 521,375
Restricted cash	34,200	41,800	45,300	39,100
Total cash, cash equivalents, and restricted cash	278,107	326,185	380,055	560,509
Restricted cash from initial capitalization of captive insurance company	2,000	2,000
Additional cash restricted at the election of management for potential insurance claims	29,200	28,500
Drilling technology companies
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash	3,000	11,300
Prepaid expenses and other
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash	30,363	39,830	38,385	32,439
Other assets.
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash	3,832	$ 2,000	$ 6,906	$ 6,695
United States
RESTRICTED CASH AND CASH EQUIVALENTS
Cash and cash equivalents	227,300
Other countries
RESTRICTED CASH AND CASH EQUIVALENTS
Cash and cash equivalents	$ 16,600