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v2.4.1.9

Income Taxes - Roll-Forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | $ 13.0 us-gaap_UnrecognizedTaxBenefits | $ 12.8 us-gaap_UnrecognizedTaxBenefits | $ 12.6 us-gaap_UnrecognizedTaxBenefits
Reductions for tax positions of prior periods | (4.0)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions |  |
Additions for tax positions of prior periods | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 0.8 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Additions related to tax positions taken in the current period | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions |  | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Reductions due to lapsed statutes of limitations | (3.1)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | (0.6)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | (0.2)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations
Closing balance at December 31 | 6.2 us-gaap_UnrecognizedTaxBenefits | 13.0 us-gaap_UnrecognizedTaxBenefits | 12.8 us-gaap_UnrecognizedTaxBenefits
Current | 0 us-gaap_LiabilityForUncertainTaxPositionsCurrent | (6.8)us-gaap_LiabilityForUncertainTaxPositionsCurrent | (3.0)us-gaap_LiabilityForUncertainTaxPositionsCurrent
Non-current | 6.2 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent | 6.2 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent | 9.8 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent
Interest and Penalties [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 1.1 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.6 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.4 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Reductions for tax positions of prior periods | (0.4)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember |  |
Additions for tax positions of prior periods | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.6 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Additions related to tax positions taken in the current period | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember |  | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Reductions due to lapsed statutes of limitations | (0.2)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | (0.1)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Closing balance at December 31 | 0.5 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 1.1 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.6 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Current | 0 us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | (0.6)us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | (0.3)us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Non-current | 0.5 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.5 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember | 0.3 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Unrecognized Tax Benefits [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 11.9 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 12.2 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 12.2 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Reductions for tax positions of prior periods | (3.6)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember |  |
Additions for tax positions of prior periods | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Additions related to tax positions taken in the current period | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember |  | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Reductions due to lapsed statutes of limitations | (2.9)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | (0.5)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | (0.2)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Closing balance at December 31 | 5.7 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 11.9 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | 12.2 us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Current | 0 us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | (6.2)us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | (2.7)us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Non-current | $ 5.7 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | $ 5.7 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember | $ 9.5 us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember

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- Definition The current portion of the amount recognized for uncertain tax positions as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The noncurrent portion of the amount recognized for uncertain tax positions as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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