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Income Taxes - Roll-Forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Opening balance at January 1, 2015	$ 6.2us-gaap_UnrecognizedTaxBenefits
Additions for tax positions of prior periods	0.1us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Closing balance at March 31, 2015	6.3us-gaap_UnrecognizedTaxBenefits
Current	0us-gaap_LiabilityForUncertainTaxPositionsCurrent
Non-current	6.3us-gaap_LiabilityForUncertainTaxPositionsNoncurrent	6.2us-gaap_LiabilityForUncertainTaxPositionsNoncurrent
Unrecognized Tax Benefits [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1, 2015	5.7us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Additions for tax positions of prior periods	0us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Closing balance at March 31, 2015	5.7us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Current	0us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Non-current	5.7us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_UnrecognizedTaxBenefitsMember
Interest and Penalties [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1, 2015	0.5us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Additions for tax positions of prior periods	0.1us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Closing balance at March 31, 2015	0.6us-gaap_UnrecognizedTaxBenefits / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Current	0us-gaap_LiabilityForUncertainTaxPositionsCurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember
Non-current	$ 0.6us-gaap_LiabilityForUncertainTaxPositionsNoncurrent / us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis = iosp_InterestAndPenaltiesMember

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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

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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

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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

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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