XML 117 R58.htm IDEA: XBRL DOCUMENT v2.4.1.9
Property, Plant and Equipment - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Property, Plant and Equipment [Abstract]      
Amounts of assets held under finance leases $ 2,200,000us-gaap_CapitalLeasesBalanceSheetAssetsByMajorClassNet $ 0us-gaap_CapitalLeasesBalanceSheetAssetsByMajorClassNet  
Depreciation charges 10,600,000us-gaap_Depreciation 8,900,000us-gaap_Depreciation 7,000,000us-gaap_Depreciation
Estimated additional cost to complete work in progress $ 1,400,000iosp_EstimatedAdditionalCostToCompleteWorkInProgress $ 2,200,000iosp_EstimatedAdditionalCostToCompleteWorkInProgress