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Stock-Based Compensation Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Maximum cash bonus under long-term incentive plan | $ 3.0 iosp_LongTermIncentivePlanMaximumBonus |
Stock Options Plan [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number exercisable and fully vested | 115,793 us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember |
Fully vested stock options with performance conditions attached | 39,000 iosp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumberPerformanceConditionsAttached / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember |
Stock option compensation cost of SEUs | 0.9 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember | 0.6 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember
Total intrinsic value of options exercised | 2.0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember | 0.5 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember
Total compensation cost related to non-vested stock options not yet recognized | 5.7 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions / us-gaap_AwardTypeAxis = us-gaap_StockOptionMember |
Expected compensation cost recognized over the weighted-average period | 2 years 4 months 2 days |
Stock Equivalent Units [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Fully vested stock options with performance conditions attached | 63,838 iosp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumberPerformanceConditionsAttached / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember |
Stock option compensation cost of SEUs | 1.0 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember | 0.6 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember
Total intrinsic value of options exercised | $ 1.9 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember | $ 3.0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember
Expected compensation cost recognized over the weighted-average period | 2 years 11 days |
Number of exercisable SEUs | 73,890 iosp_ShareBasedCompensationSharesAuthorizedUnderStockEquivalentUnitsExercisePriceRangeNumberOfExercisableOptions / us-gaap_AwardTypeAxis = iosp_StockEquivalentUnitsMember |

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- Definition Maximum bonus under long term incentive plan. + References No definition available. + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Share based compensation arrangement by share based payment award options exercisable number performance conditions attached. + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Share-based compensation shares authorized under stock equivalent units exercise price range number of exercisable options. + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested options awarded to employees as compensation. + References No definition available. + Details
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- Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Details
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- Details
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