SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RISKS AND UNCERTAINTIES - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash and cash equivalents	$ 41,800	$ 39,100
Restricted cash and cash equivalents from initial capitalization of captive insurance company	2,000
Additional cash and cash equivalents restricted at the election of management for potential insurance claims	28,500	27,700
Drilling technology companies acquisitions
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash and cash equivalents	11,300	9,400
Prepaid expenses and other
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash and cash equivalents	39,830	32,439
Other assets.
RESTRICTED CASH AND CASH EQUIVALENTS
Restricted cash and cash equivalents	$ 2,000	$ 6,695