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Pension Plans - Reconciliation of Fair Value of Plan Assets (Detail) (United Kingdom Plan [Member], Non-financial Assets and Liabilities (Level 3 Measurement) [Member], Other Assets [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
United Kingdom Plan [Member] | Non-financial Assets and Liabilities (Level 3 Measurement) [Member] | Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 38.3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	$ 31.0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember
Realized/unrealized gains/(losses):
Relating to assets still held at the reporting date	7.3iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetStillHeldGainLossIncludedInEarningsOne / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	3.5iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetStillHeldGainLossIncludedInEarningsOne / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember
Relating to assets sold during the period	0iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSoldGainLossIncludedInEarningsOne / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	0iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSoldGainLossIncludedInEarningsOne / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember
Purchases, issuances and settlements	0.7us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	3.6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember
Exchange effect	(2.2)iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetExchangeEffect / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	0.2iosp_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetExchangeEffect / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember
Ending balance	$ 44.1us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember	$ 38.3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_OtherAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_PlanNameAxis = iosp_UkPlanMember

X

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset exchange effect.

+ References

No definition available.

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X

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset sold gain loss included in earnings one.

+ References

No definition available.

+ Details

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X

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset still held gain loss included in earnings one.

+ References

No definition available.

+ Details

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- Definition

Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph c

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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