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Stock-Based Compensation Plans - Summary of Fair Value of Balance Sheet Dates (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Balance at January 1	$ 0.1iosp_FairValueOfLiabilityCashSettledStockAppreciationRights	$ 0iosp_FairValueOfLiabilityCashSettledStockAppreciationRights
Compensation charge for the period	0.1iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights	0.1iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights
Balance at March 31	$ 0.2iosp_FairValueOfLiabilityCashSettledStockAppreciationRights	$ 0.1iosp_FairValueOfLiabilityCashSettledStockAppreciationRights

X

- Definition

Change in fair value of liability cash-settled stock appreciation rights.

+ References

No definition available.

+ Details

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X

- Definition

Fair value of liability cash-settled stock appreciation rights.

+ References

No definition available.

+ Details

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Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
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X

- Details

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