Net Commission Earned Under the Marketing Agreement (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Marketing Agreement [Line Items]
Gross commission	$ 85.2	$ 81.8	$ 81.3
Contribution expenses	(20.0)	(20.0)	(20.0)
Amortization of marketing fee	(0.8)	(0.8)	(0.8)
Net commission income	64.4	61.0	60.5
Reimbursements associated with Marketing Agreement	63.0	62.0	79.6
Total net sales associated with Marketing Agreement	$ 127.4	$ 123.0	$ 140.1
Monsanto Marketing Agreement | NA Consumer [Member]
Marketing Agreement [Line Items]
Useful life of consideration for marketing rights	20 years