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Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Income tax, Uncertain tax position description	The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has greater than 50 percent likelihood of being realized upon settlement.

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- Definition

Uncertain Income Tax Position Description

+ References

No definition available.

+ Details

Name:	iosp_UncertainIncomeTaxPositionDescription
Namespace Prefix:	iosp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

Name:	us-gaap_AccountingPoliciesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration