Acquisitions - Summary of Acquisition and Integration Related Charges Incurred (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition [Line Items]
Total acquisition and integration related charges	$ 37,300,000	$ 61,100,000	$ 24,400,000
AAG Acquisition [Member]
Business Acquisition [Line Items]
Total acquisition and integration related charges	14,600,000	21,800,000	0
HHI Business
Business Acquisition [Line Items]
Total acquisition and integration related charges	13,300,000	12,000,000	11,100,000
Salix Animal Health LLC [Member]
Business Acquisition [Line Items]
Total acquisition and integration related charges	2,100,000	10,700,000	0
European IAMS and Eukanuba [Member]
Business Acquisition [Line Items]
Total acquisition and integration related charges	3,500,000	9,300,000	0
Other
Business Acquisition [Line Items]
Total acquisition and integration related charges	$ 3,800,000	$ 7,300,000	$ 13,300,000