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Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2018
Accounting Policies [Abstract] |
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 greater than 50 percent likelihood of being realized upon settlement.

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- Definition Uncertain Income Tax Position Description + References No definition available. + Details
Name: | iosp_UncertainIncomeTaxPositionDescription
Namespace Prefix: | iosp_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration