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Income Taxes - Details of Deferred Tax Asset Valuation Allowance (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Tax Disclosure [Abstract] |  |  |
At January 1 | $ 0 us-gaap_DeferredTaxAssetsValuationAllowance | $ 0 us-gaap_DeferredTaxAssetsValuationAllowance | $ (7.5)us-gaap_DeferredTaxAssetsValuationAllowance
Change in foreign tax credits | 0 iosp_ForeignTaxCreditChangeDuringPeriod | 0 iosp_ForeignTaxCreditChangeDuringPeriod | 7.5 iosp_ForeignTaxCreditChangeDuringPeriod
At December 31 | $ 0 us-gaap_DeferredTaxAssetsValuationAllowance | $ 0 us-gaap_DeferredTaxAssetsValuationAllowance | $ 0 us-gaap_DeferredTaxAssetsValuationAllowance

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- Definition Foreign Tax Credit Change During Period + References No definition available. + Details
Name: | iosp_ForeignTaxCreditChangeDuringPeriod
Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319 + Details
Name: | us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration