SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - LOAN RECEIVABLE (Details) - USD ($)	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable in other current assets	$ 9,400,000	$ 8,900,000
Loans receivable in other noncurrent assets	$ 40,700,000	40,400,000
Threshold period in establishing allowance for doubtful accounts	60 days
Allowance for doubtful accounts	$ 0	$ 0
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan term	3 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan term	10 years