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Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Accounting Policies [Line Items] |  |  |
Impairment of goodwill | $ 0 us-gaap_GoodwillImpairmentLoss | $ 1.3 us-gaap_GoodwillImpairmentLoss | $ 1.2 us-gaap_GoodwillImpairmentLoss
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 a greater than 50% likelihood of being realized upon settlement. |  |
Minimum [Member] |  |  |
Accounting Policies [Line Items] |  |  |
Short-term investments maturity period | 3 months |  |
Maximum [Member] |  |  |
Accounting Policies [Line Items] |  |  |
Cash equivalents maturity period | 3 months |  |
Short-term investments maturity period | 12 months |  |
Fuel Specialties [Member] |  |  |
Accounting Policies [Line Items] |  |  |
Impairment of goodwill | 0 us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = iosp_FuelSpecialtiesMember | 0 us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = iosp_FuelSpecialtiesMember |
Performance Chemicals [Member] |  |  |
Accounting Policies [Line Items] |  |  |
Impairment of goodwill | $ 0 us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = iosp_PerformanceChemicalsMember | $ 0 us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = iosp_PerformanceChemicalsMember |

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- Details
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Namespace Prefix: | iosp_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Cash And Cash Equivalents Maturity Period + References No definition available. + Details
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Namespace Prefix: | iosp_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Short Term Investment Maturity Period + References No definition available. + Details
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Namespace Prefix: | iosp_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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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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- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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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
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |