SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment, Intangible Assets and Insurance (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets:
Impairment of goodwill, indefinite-lived assets or identifiable intangible assets with finite lives	$ 0.0	$ 0.0
Insurance
Letter of credit issued for worker's compensation insurance carrier as part of the entity's self-insured loss control program	$ 0.4
Buildings
Property and Equipment
Estimated useful lives	40 years
Warehouse equipment | Minimum
Property and Equipment
Estimated useful lives	5 years
Warehouse equipment | Maximum
Property and Equipment
Estimated useful lives	7 years
Furniture, fixtures and leasehold improvements | Minimum
Property and Equipment
Estimated useful lives	2 years
Furniture, fixtures and leasehold improvements | Maximum
Property and Equipment
Estimated useful lives	12 years
Vehicles | Minimum
Property and Equipment
Estimated useful lives	2 years
Vehicles | Maximum
Property and Equipment
Estimated useful lives	5 years