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Pension Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2010 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2010 | Dec. 31, 2015 | Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Retirement age of service |  | 65 years |  |  |  |
Reduced in Projected Benefit Obligation (PBO) | $ 17.1 iosp_DefinedBenefitPlanBenefitObligationPeriodDecreaseDueToPensionIncreaseExchangeProgram |  |  |  |  |
Remaining life expectancy of Plan pensioners |  |  |  | 15 years |  |
Average remaining life expectancy of the inactive participants |  | 24 years |  |  |  |
Annual cash contribution |  | 11.4 iosp_AnnualCashContribution |  |  |  |
Maximum percentage of Plan's assets invested in individual company's investment funds |  | 5.00%iosp_MaximumPercentOfInvestmentInIndividualSecurities |  |  |  |
Accumulated benefit obligation for the Plan |  | 817.1 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation | 819.8 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation |  |  |
Amount of contributions to defined contribution schemes |  | 8.2 iosp_AmountOfContributionsToDefinedContributionSchemes | 7.7 iosp_AmountOfContributionsToDefinedContributionSchemes |  |  |
United Kingdom Government Gilts [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Percentage of asset allocation, actual |  | 40.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = iosp_UnitedKingdomGovernmentGiltsMember | 25.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = iosp_UnitedKingdomGovernmentGiltsMember |  |  |
Debt Securities [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Asset allocation |  | 65.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember |  |  |  |
Equity Securities [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Asset allocation |  | 35.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember |  |  |  |
Forecast [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Percentage change in discount rate |  |  |  |  | 0.25%iosp_DefiniteBenefitPlanExpectedChangeInDiscountRate / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |
Amount change in PBO due to discount rate |  |  |  |  | 29 iosp_DefiniteBenefitPlanExpectedChangeProjectBenefitObligationDueToDiscountRateChange / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |
Amount change in net pension credit due to discount rate |  |  |  |  | 0.3 iosp_DefiniteBenefitPlanExpectedNetPensionCostDueChangeInDiscountRate / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |
Amount change in PBO due to change price inflation |  |  |  |  | 22 iosp_DefiniteBenefitPlanExpectedChangeProjectBenefitObligationDueToInflationRateChange / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |
Percentage change in price inflation |  |  |  |  | 0.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |
German Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Amount of unrecognized actuarial net losses |  | 2.7 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax / us-gaap_PlanNameAxis = iosp_GermanPlanMember |  |  |  |
Amount of unrecognized actuarial net losses, net of tax |  | $ 0.7 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax / us-gaap_PlanNameAxis = iosp_GermanPlanMember |  |  |  |
United Kingdom Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Asset allocation |  | 100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_PlanNameAxis = iosp_UkPlanMember | 100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_PlanNameAxis = iosp_UkPlanMember |  |  | 100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_PlanNameAxis = iosp_UkPlanMember
United Kingdom Plan [Member] | Index-Tracking Funds [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Percentage of asset allocation, actual |  | 50.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = iosp_IndexTrackingFundsMember / us-gaap_PlanNameAxis = iosp_UkPlanMember | 55.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = iosp_IndexTrackingFundsMember / us-gaap_PlanNameAxis = iosp_UkPlanMember |  |  |
United Kingdom Plan [Member] | Debt Securities [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Asset allocation |  | 63.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember | 61.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember |  |  | 61.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember
United Kingdom Plan [Member] | Equity Securities [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Asset allocation |  | 32.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember | 35.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember |  |  | 33.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_PlanNameAxis = iosp_UkPlanMember

X
- Definition Amount of contributions to defined contribution schemes. + References No definition available. + Details
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- Definition Annual cash contribution. + References No definition available. + Details
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- Definition Average Remaining Life Expectancy Of Inactive Participants + References No definition available. + Details
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- Definition Defined benefit plan benefit obligation period decrease due to pension increase exchange program. + References No definition available. + Details
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- Definition Defined benefit plan benefit prior service credit amortization period. + References No definition available. + Details
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- Definition Definite benefit plan employee retirement age. + References No definition available. + Details
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- Definition Definite benefit plan expected change in discount rate. + References No definition available. + Details
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Balance Type: | na
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- Definition Definite benefit plan expected change project benefit obligation due to discount rate change. + References No definition available. + Details
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Namespace Prefix: | iosp_
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- Definition Definite benefit plan expected change project benefit obligation due to inflation rate change. + References No definition available. + Details
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- Definition Definite benefit plan expected net pension cost due change in discount rate. + References No definition available. + Details
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- Definition Maximum Percent of investment in individual securities. + References No definition available. + Details
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- Definition For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503844 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money for the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Details
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- Definition Target allocation of investments of this type to total plan assets presented on a weighted average basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of tax expense (benefit) related to (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Details
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- Details
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