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Property, Plant and Equipment - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Property, Plant and Equipment [Abstract] |  |  |
Amounts of assets held under finance leases | $ 2,200,000 us-gaap_CapitalLeasesBalanceSheetAssetsByMajorClassNet | $ 0 us-gaap_CapitalLeasesBalanceSheetAssetsByMajorClassNet |
Depreciation charges | 10,600,000 us-gaap_Depreciation | 8,900,000 us-gaap_Depreciation | 7,000,000 us-gaap_Depreciation
Estimated additional cost to complete work in progress | $ 1,400,000 iosp_EstimatedAdditionalCostToCompleteWorkInProgress | $ 2,200,000 iosp_EstimatedAdditionalCostToCompleteWorkInProgress |

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- Definition Estimated Additional Cost To Complete Work In Progress + References No definition available. + Details
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Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The total gross amount less the charge for the use of the long-lived depreciable assets subject to a lease meeting the criteria for capitalization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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