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Pension Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |
Net pension charge | $ 0 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost | $ 0.8 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
German Plan [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net pension charge | $ 0.2 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_PlanNameAxis = iosp_GermanPlanMember | $ 0.2 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_PlanNameAxis = iosp_GermanPlanMember

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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Definition The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. + 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 (j) -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 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |