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Goodwill - Summary of Goodwill (Parenthetical) (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Fuel Specialties [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization | $ 8.7 | $ 8.7 | $ 8.7
Performance Chemicals [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization | 0.3 | 0.3 | 0.3
Octane Additives [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization | $ 289.5 | $ 289.5 | $ 289.5

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- Definition Goodwill historical accumulated amortization. + References No definition available. + Details
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Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_GoodwillLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=iosp_FuelSpecialtiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=iosp_PerformanceChemicalsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=iosp_OctaneAdditivesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |