Acquisitions (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended				1 Months Ended	0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Accrued Liabilities [Member]	Sep. 30, 2014 Other Noncurrent Liabilities [Member]	Dec. 28, 2012 Ford Wholesale Co [Member]	Nov. 01, 2012 Mcclure-Johnston Co [Member]
Business Acquisition [Line Items]
Business acquisition total cost		$ 64.6
Business acquisition, goodwill		27.8
Business Acquisition, sales reported by acquired entity for last annual period					60	85
Business acquisition, purchase price adjustments and post closing indemnification claims, liabilities			0.2	3.0
Number of Stores		19				14
Legal Fees	0.1	0.7
Amount Of Acquisition Prices That Remain In Escrow	$ 3.2