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Long-Term Debt - Schedule of Long-Term Debt (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Debt Instrument [Line Items]    
Long-term debt $ 139.2us-gaap_LongTermDebt $ 139.4us-gaap_LongTermDebt
Less current portion (0.2)us-gaap_LongTermDebtCurrent (0.4)us-gaap_LongTermDebtCurrent
Long-term debt, net of current portion 139.0us-gaap_LongTermDebtNoncurrent 139.0us-gaap_LongTermDebtNoncurrent
Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Long-term debt 139.0us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
139.0us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
Other Long-Term Debt [Member]    
Debt Instrument [Line Items]    
Long-term debt $ 0.2us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= iosp_OtherLongTermDebtMember
$ 0.4us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= iosp_OtherLongTermDebtMember