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Long-Term Debt - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended 0 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 31, 2014
Aug. 28, 2013
Dec. 14, 2011
Sep. 13, 2011
Installment
Schedule Of Debt Instruments [Line Items]                
Revolving credit facility, drawn down amount $ 30,000,000us-gaap_ProceedsFromLinesOfCredit $ 53,000,000us-gaap_ProceedsFromLinesOfCredit $ 145,000,000us-gaap_ProceedsFromLinesOfCredit $ 18,000,000us-gaap_ProceedsFromLinesOfCredit        
Maximum ratio of net debt to EBITDA   2.5iosp_MaximumDebtToEarningBeforeInterestTaxDepreciationAndAmortizationRatio            
Minimum ratio of EBITDA to net interest   4.0iosp_MinimumEarningBeforeInterestTaxDepreciationAndAmortizationToInterestRatio            
Weighted average rate of interest on borrowings 1.60%us-gaap_LongtermDebtWeightedAverageInterestRate 1.70%us-gaap_LongtermDebtWeightedAverageInterestRate 1.60%us-gaap_LongtermDebtWeightedAverageInterestRate          
Payments of interest on long-term debt   2,300,000us-gaap_InterestExpenseDebt 1,000,000us-gaap_InterestExpenseDebt 500,000us-gaap_InterestExpenseDebt        
Net cash outflows in respect of refinancing costs   100,000us-gaap_PaymentsOfDebtIssuanceCosts 900,000us-gaap_PaymentsOfDebtIssuanceCosts 0us-gaap_PaymentsOfDebtIssuanceCosts        
Revolving Credit Facility [Member]                
Schedule Of Debt Instruments [Line Items]                
Revolving credit facility term             5 years  
Credit facility maximum borrowing capacity         200,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		 100,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		 100,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		  
Expiration date of facility   Dec. 14, 2016       Dec. 31, 2016 Dec. 14, 2016  
Credit facility, borrowings capacity increased amount         20,000,000us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		      
Revolving Credit Facility [Member] | Amended Credit Facility [Member]                
Schedule Of Debt Instruments [Line Items]                
Revolving credit facility term           5 years    
Credit facility maximum borrowing capacity           150,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= iosp_AmendedRevolvingFacilityMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember		    
Previous Finance Facility [Member]                
Schedule Of Debt Instruments [Line Items]                
Expiration date of facility             Feb. 06, 2012  
Additional Amount to be Committed by Lenders [Member]                
Schedule Of Debt Instruments [Line Items]                
Revolving credit facility, drawn down amount           50,000,000us-gaap_ProceedsFromLinesOfCredit
/ us-gaap_LongtermDebtTypeAxis
= iosp_AdditionalAmountToBeCommittedByLendersMember		    
Promissory Note [Member] | NewMarket Corporation [Member]                
Schedule Of Debt Instruments [Line Items]                
Promissory note issued               $ 15,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= iosp_PromissoryNoteMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= iosp_NewMarketCorporationMember
Carrying simple interest per annum               1.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= iosp_PromissoryNoteMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= iosp_NewMarketCorporationMember
Number of repayment installments               3iosp_NumberOfRepaymentInstallment
/ us-gaap_LongtermDebtTypeAxis
= iosp_PromissoryNoteMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= iosp_NewMarketCorporationMember
Minimum [Member] | Revolving Credit Facility [Member]                
Schedule Of Debt Instruments [Line Items]                
Margin rate based on U.S. dollar LIBOR             1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maximum [Member] | Revolving Credit Facility [Member]                
Schedule Of Debt Instruments [Line Items]                
Margin rate based on U.S. dollar LIBOR             2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember