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Goodwill - Summary of Goodwill (Parenthetical) (Detail) - USD ($) $ in Millions | Sep. 30, 2019 | Sep. 30, 2018
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Goodwill [Line Items] |  |
Historical accumulated amortization | $ 298.5 | $ 298.5

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- Definition Goodwill historical accumulated amortization. + References No definition available. + Details
Name: | iosp_GoodwillHistoricalAccumulatedAmortization
Namespace Prefix: | iosp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_GoodwillLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration