SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - SALES TAX ACCOUNTING (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Sales tax	$ 41.7	$ 39.4	$ 31.0
Sales tax, percentage	6.625%	6.875%	7.00%