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Stock-Based Compensation Long-Term Performance Restricted Stock Unit Award Monte Carlo Pricing Model Assumptions (Details) (Restricted Stock Units (RSUs) [Member], USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted-average fair value $ 35.30us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue [1] $ 35.38us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue [1]
Long Term Performance Restricted Stock Award [Member]
    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember		 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember
Expected volatility 30.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember		 30.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember
Risk-free interest rate 0.70%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember		 0.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember
Expected term (years) 2 years 1 month 15 days 1 year 5 months 0 days
Weighted-average fair value $ 33.46us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember		 $ 28.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= itri_LongTermPerformanceRestrictedStockAwardMember
[1] Restricted stock units granted in 2014 and 2015 do not include awards under the Performance Award Agreement for the respective years, as these awards are not granted until attainment of annual performance goals has been determined at the conclusion of the performance period, which had not occurred as of March 31, 2014 and 2015, respectively.