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Goodwill - Summary of Goodwill (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
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Fuel Specialties [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization | $ 8.7 iosp_GoodwillHistoricalAccumulatedAmortization / us-gaap_StatementBusinessSegmentsAxis = iosp_FuelSpecialtiesMember |  |
Performance Chemicals [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization |  | 0.3 iosp_GoodwillHistoricalAccumulatedAmortization / us-gaap_StatementBusinessSegmentsAxis = iosp_PerformanceChemicalsMember |
Octane Additives [Member] |  |  |
Goodwill [Line Items] |  |  |
Historical accumulated amortization |  |  | $ 289.5 iosp_GoodwillHistoricalAccumulatedAmortization / us-gaap_StatementBusinessSegmentsAxis = iosp_OctaneAdditivesMember

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

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- 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: |

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

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