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Stock-Based Compensation Plans - Summary of Fair Value of Balance Sheet Dates (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |  |
Balance at January 1 | $ 0.1 iosp_FairValueOfLiabilityCashSettledStockAppreciationRights | $ 0 iosp_FairValueOfLiabilityCashSettledStockAppreciationRights
Compensation charge for the period | 0.1 iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights | 0.1 iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights
Balance at March 31 | $ 0.2 iosp_FairValueOfLiabilityCashSettledStockAppreciationRights | $ 0.1 iosp_FairValueOfLiabilityCashSettledStockAppreciationRights

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- Definition Change in fair value of liability cash-settled stock appreciation rights. + References No definition available. + Details
Name: | iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights
Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Fair value of liability cash-settled stock appreciation rights. + References No definition available. + Details
Name: | iosp_FairValueOfLiabilityCashSettledStockAppreciationRights
Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration