Stockholders' Equity and Stock-Based Compensation Plans - Fair Value of Liability Cash-Settled Stock Appreciation Rights (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Balance at January 1	$ 0
Compensation charge for the period	0.1
Balance at June 30	$ 0.1

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

No definition available.

Name:	iosp_ChangeInFairValueOfLiabilityCashSettledStockAppreciationRights
Namespace Prefix:	iosp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration