SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017
RESTRICTED Cash and Investments [Abstract]
Cash	$ 334,775	$ 284,355	$ 306,426	$ 521,375
Restricted cash	34,300	41,800	41,500	39,100
Total cash, cash equivalents, and restricted cash	369,106	326,185	347,942	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	29,300	28,500
Drilling technology companies
RESTRICTED Cash and Investments [Abstract]
Restricted cash	3,000	11,300
Prepaid expenses and other
RESTRICTED Cash and Investments [Abstract]
Restricted cash	30,543	39,830	34,614	32,439
Other assets
RESTRICTED Cash and Investments [Abstract]
Restricted cash	3,788	$ 2,000	$ 6,902	$ 6,695
United States
RESTRICTED Cash and Investments [Abstract]
Cash	318,900
Other countries
RESTRICTED Cash and Investments [Abstract]
Cash	$ 15,900