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Segmental Reporting and Geographical Area Data - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Segment Reporting Information [Line Items]      
Number of segments 3us-gaap_NumberOfOperatingSegments    
Shell [Member]      
Segment Reporting Information [Line Items]      
Amount of net group sales $ 81.9us-gaap_Revenues
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember
$ 83.1us-gaap_Revenues
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember
$ 82.9us-gaap_Revenues
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember
Sales [Member] | Shell [Member]      
Segment Reporting Information [Line Items]      
Percentage of net group sales 8.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember
10.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember
11.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesMember
/ us-gaap_MajorCustomersAxis
= iosp_ShellMember