Acquisitions - Additional Information (Detail) - USD ($) $ in Millions				3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 16, 2015	Dec. 31, 2014	Oct. 01, 2014	Dec. 31, 2014	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	May 21, 2015	Oct. 31, 2014	Oct. 06, 2014	Jan. 02, 2014	Sep. 30, 2013	Feb. 14, 2013
Business Acquisition [Line Items]
Goodwill (Note 12)						$ 2,478.4	$ 2,487.4						$ 1,524.8
Estimated Income tax rate						35.00%		35.00%
Cash consideration							1,328.4	$ 27.3
HGI
Business Acquisition [Line Items]
Acquisition related charges						$ 0.2	0.4	4.2
Compass Production Partners [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						$ 118.8
Technology Assets [Member] | Minimum [Member]
Business Acquisition [Line Items]
Amortization period, intangible asset						4 years
Technology Assets [Member] | Maximum
Business Acquisition [Line Items]
Amortization period, intangible asset						18 years
Customer Relationships [Member]
Business Acquisition [Line Items]
Retention Rate						95.00%
Estimated Income tax rate						38.00%
Business Acquisition Contingent Consideration Key Assumptions Discount Rate						9.50%
Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Amortization period, intangible asset						2 years
Customer Relationships [Member] | Maximum
Business Acquisition [Line Items]
Amortization period, intangible asset						20 years
Compass Production Partners G.P. [Member]
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired						100.00%
AAG Acquisition [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)						$ 975.4
Property, plant and equipment						37.6
Goodwill (Note 12)						418.0			$ 418.0
Inventory						82.5
Business Combination, Consideration Transferred						929.3
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net						$ 929.3
Business Acquisition, Pro Forma Net Income (Loss)							$ (517.5)	(71.4)
Business Acquisition, Goodwill, Expected Tax Deductible Amount									4.9
AAG Acquisition [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						15 years
Goodwill (Note 12)									63.0
AAG Acquisition [Member] | Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate						2.00%
AAG Acquisition [Member] | Customer Relationships [Member] | Maximum
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate						12.10%
AAG Acquisition [Member] | Tradenames Trademarks And Patents [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)									$ 295.0
Compass | EXCO [Member]
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														24.50%
Compass | HGI
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired						74.40%
Compass | HGI Energy Holdings, LLC
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														73.50%
Compass | EXCO/HGI General Partner
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														2.00%
The Liquid Fence Company [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other								1.5
Goodwill (Note 12)												$ 7.1
Property, plant and equipment												0.1
Business Combination, Consideration Transferred, Liabilities Incurred								9.5
Goodwill (Note 12)			$ 26.9									26.9
Inventory												2.1
Business Combination, Consideration Transferred								35.8
Payments to Acquire Businesses, Gross								$ 24.8
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net												$ 35.8
The Liquid Fence Company [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				15 years
Goodwill (Note 12)			1.3
The Liquid Fence Company [Member] | Tradenames Trademarks And Patents [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)			5.1
Compass Production Partners [Member]
Business Acquisition [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired											25.50%
Compass Production Partners [Member] | Compass Production Partners [Member]
Business Acquisition [Line Items]
Percentage Of Ownership Interest						99.80%
Salix Animal Health LLC [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)	$ 71.5
Property, plant and equipment	1.2
Business Combination, Consideration Transferred, Liabilities Incurred						$ 1.5
Goodwill (Note 12)	55.5
Inventory	17.0
Business Combination, Consideration Transferred						148.3
Payments to Acquire Businesses, Gross						$ 146.8
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	148.3
Business Acquisition, Goodwill, Expected Tax Deductible Amount	$ 24.7
Salix Animal Health LLC [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Retention Rate	92.50%
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	13 years
Estimated Income tax rate	38.00%
Goodwill (Note 12)	$ 35.4
Salix Animal Health LLC [Member] | Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate	0.00%
Business Acquisition Contingent Consideration Key Assumptions Discount Rate	12.00%
Salix Animal Health LLC [Member] | Customer Relationships [Member] | Maximum
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate	12.10%
Business Acquisition Contingent Consideration Key Assumptions Discount Rate	13.00%
Salix Animal Health LLC [Member] | Tradenames Trademarks And Patents [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)	$ 17.0
European IAMS and Eukanuba [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)		$ 4.0		$ 4.0
Property, plant and equipment		58.3		58.3
Goodwill (Note 12)		39.6		39.6
Inventory		16.3		16.3
Business Combination, Consideration Transferred				115.7
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net		$ 115.7		115.7
European IAMS and Eukanuba [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						15 years
Estimated Income tax rate		25.00%
Goodwill (Note 12)		$ 10.5		$ 10.5
Business Acquisition Contingent Consideration Key Assumptions Discount Rate		12.50%
European IAMS and Eukanuba [Member] | Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate		0.00%
Retention Rate		90.00%		90.00%
European IAMS and Eukanuba [Member] | Customer Relationships [Member] | Maximum
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate		5.60%
Retention Rate		100.00%		100.00%
European IAMS and Eukanuba [Member] | Tradenames Trademarks And Patents [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)		$ 25.5		$ 25.5
Tell Manufacturing [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)			7.1
Property, plant and equipment			12.5
Goodwill (Note 12)			12.5
Inventory			7.2
Business combination, assets acquired			30.3
Business Combination, Consideration Transferred				$ 30.3
Business Acquisition, Goodwill, Expected Tax Deductible Amount			$ 7.1
Tell Manufacturing [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Retention Rate			90.00%
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				13 years
Estimated Income tax rate			38.00%
Goodwill (Note 12)			$ 8.5
Business Acquisition Contingent Consideration Key Assumptions Discount Rate					20.00%
Tell Manufacturing [Member] | Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate			2.50%
Tell Manufacturing [Member] | Customer Relationships [Member] | Maximum
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate			7.10%
Tell Manufacturing [Member] | Tradenames Trademarks And Patents [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)			$ 4.0
Ability Re [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Liabilities Incurred				$ 2.8
Business Combination, Consideration Transferred				19.2
Payments to Acquire Businesses, Gross				$ 17.9
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net										$ 19.2
Interest Expense [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)						$ 35.7
Acquisition-related Costs [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)						47.3
Fair Value Adjustment to Inventory [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)						$ 18.8
Share-based compensation [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments [Table Text Block]						10.4
Cost Approach Valuation Technique [Member] | Salix Animal Health LLC [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment, Measurement Basis, Percentage of Total	98.00%
Cost Approach Valuation Technique [Member] | Tell Manufacturing [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment, Measurement Basis, Percentage of Total			97.00%
Market Approach Valuation Technique [Member] | Salix Animal Health LLC [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment, Measurement Basis, Percentage of Total	2.00%
Market Approach Valuation Technique [Member] | Tell Manufacturing [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment, Measurement Basis, Percentage of Total			3.00%