Amount of contributions to defined contribution schemes.

No definition available.

Name:	iosp_AmountOfContributionsToDefinedContributionSchemes
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Annual cash contribution.

+ References

No definition available.

+ Details

Name:	iosp_AnnualCashContribution
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Average Remaining Life Expectancy Of Inactive Participants

+ References

No definition available.

+ Details

Name:	iosp_AverageRemainingLifeExpectancyOfInactiveParticipants
Namespace Prefix:	iosp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan benefit obligation period decrease due to pension increase exchange program.

+ References

No definition available.

+ Details

Name:	iosp_DefinedBenefitPlanBenefitObligationPeriodDecreaseDueToPensionIncreaseExchangeProgram
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Defined benefit plan benefit prior service credit amortization period.

+ References

No definition available.

+ Details

Name:	iosp_DefinedBenefitPlanBenefitPriorServiceCreditAmortizationPeriod
Namespace Prefix:	iosp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Definite benefit plan employee retirement age.

+ References

No definition available.

+ Details

Name:	iosp_DefiniteBenefitPlanEmployeeRetirementAge
Namespace Prefix:	iosp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Definite benefit plan expected change in discount rate.

+ References

No definition available.

+ Details

Name:	iosp_DefiniteBenefitPlanExpectedChangeInDiscountRate
Namespace Prefix:	iosp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Definite benefit plan expected change project benefit obligation due to discount rate change.

+ References

No definition available.

+ Details

Name:	iosp_DefiniteBenefitPlanExpectedChangeProjectBenefitObligationDueToDiscountRateChange
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Definite benefit plan expected change project benefit obligation due to inflation rate change.

+ References

No definition available.

+ Details

Name:	iosp_DefiniteBenefitPlanExpectedChangeProjectBenefitObligationDueToInflationRateChange
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Definite benefit plan expected net pension cost due change in discount rate.

+ References

No definition available.

+ Details

Name:	iosp_DefiniteBenefitPlanExpectedNetPensionCostDueChangeInDiscountRate
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum Percent of investment in individual securities.

+ References

No definition available.

+ Details

Name:	iosp_MaximumPercentOfInvestmentInIndividualSecurities
Namespace Prefix:	iosp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The interest rate used to adjust for the time value of money for the plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

Name:	us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Name:	us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=iosp_UnitedKingdomGovernmentGiltsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=iosp_GermanPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=iosp_UkPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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
Remaining life expectancy of Plan pensioners				15 years
Average remaining life expectancy of the inactive participants		24 years
Annual cash contribution		11.4iosp_AnnualCashContribution
Maximum percentage of Plan's assets invested in individual company's investment funds		5.00%
Accumulated benefit obligation for the Plan		817.1	819.8
Amount of contributions to defined contribution schemes		8.2	7.7
United Kingdom Government Gilts [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of asset allocation, actual		40.00%	25.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		65.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		35.00%
Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage change in discount rate					0.25%
Amount change in PBO due to discount rate					29
Amount change in net pension credit due to discount rate					0.3
Amount change in PBO due to change price inflation					22
Percentage change in price inflation					0.25%
German Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Amount of unrecognized actuarial net losses		2.7
Amount of unrecognized actuarial net losses, net of tax		$ 0.7
United Kingdom Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		100.00%	100.00%			100.00%
United Kingdom Plan [Member] \| Index-Tracking Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of asset allocation, actual		50.00%	55.00%
United Kingdom Plan [Member] \| Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		63.00%	61.00%			61.00%
United Kingdom Plan [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		32.00%	35.00%			33.00%