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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - SALES TAX ACCOUNTING (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Jan. 01, 2017
Principal Transaction Revenue [Line Items]
Sales tax	$ 18.7	$ 16.9	$ 31.9	$ 28.1
NEW JERSEY
Principal Transaction Revenue [Line Items]
State sales tax, percent		7.00%		7.00%	6.625%	6.875%