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Defined Benefit Pension Plans Significant Actuarial Weighted Assumptions (Discount Rate) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 2.36%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate 3.76%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate 3.36%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Percentage of Benefit Plans Denominated in Euro [Domain]      
Defined Benefit Plan Disclosure [Line Items]      
Percentage of benefit plans denominated in euro 94%    
Euro Denominated Benefit Plans [Domain]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Support, Methodology and Source Data we use two discount rates, with consideration of the duration of the plans, using a hypothetical yield curve developed from euro-denominated AA-rated corporate bond issues, partially weighted for market value, with minimum amounts outstanding of €500 million for bonds with less than 10 years to maturity and €50 million for bonds with 10 or more years to maturity, and excluding the highest and lowest yielding 10% of bonds within each maturity group.    
Shorter duration euro denominated defined benefit plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 1.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= itri_ShorterDurationEuroDenominatedDefinedBenefitPlansMember
   
Longer duration euro denominated defined benefit plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 2.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= itri_LongerDurationEuroDenominatedDefinedBenefitPlansMember
   
Defined Benefit Obligations [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Change in Discount Rate 140 basis point    
Actuarial (gain) loss 25,838us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= itri_DefinedBenefitObligationsMember
$ (6,160)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= itri_DefinedBenefitObligationsMember