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Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounting Policies [Line Items]      
Impairment of goodwill $ 0us-gaap_GoodwillImpairmentLoss $ 1.3us-gaap_GoodwillImpairmentLoss $ 1.2us-gaap_GoodwillImpairmentLoss
Income tax, Uncertain tax position description The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon settlement.    
Minimum [Member]      
Accounting Policies [Line Items]      
Short-term investments maturity period 3 months    
Maximum [Member]      
Accounting Policies [Line Items]      
Cash equivalents maturity period 3 months    
Short-term investments maturity period 12 months    
Fuel Specialties [Member]      
Accounting Policies [Line Items]      
Impairment of goodwill 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= iosp_FuelSpecialtiesMember		 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= iosp_FuelSpecialtiesMember		  
Performance Chemicals [Member]      
Accounting Policies [Line Items]      
Impairment of goodwill $ 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= iosp_PerformanceChemicalsMember		 $ 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= iosp_PerformanceChemicalsMember