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Segment Reporting and Geographical Area Data - Additional Information (Detail) - Customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Number of significant customers with sales greater than 10%	0	0	0

X

- Definition

Number of customers representing greater than ten percent of net sales.

+ References

No definition available.

+ Details

Name:	iosp_NumberOfCustomersRepresentingGreaterThanTenPercentOfNetSales
Namespace Prefix:	iosp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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