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Income Taxes (Reconciliation Of Income Taxes At The U.S. Federal Statutory Income Tax Rate To Effective Tax Rate) (Details)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Taxes [Abstract]      
U.S. federal statutory tax rate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Foreign taxes greater (less) than federal statutory rate (2.00%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential 2.00%us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (5.00%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential
Research and development tax credits (2.00%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch (7.00%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch  
Enhanced deduction for certain research and development expenses (8.00%)nati_EffectiveIncomeTaxRateReconciliationEnhancedDeductionForCertainResearchAndDevelopmentExpenses (13.00%)nati_EffectiveIncomeTaxRateReconciliationEnhancedDeductionForCertainResearchAndDevelopmentExpenses (15.00%)nati_EffectiveIncomeTaxRateReconciliationEnhancedDeductionForCertainResearchAndDevelopmentExpenses
State income taxes, net of federal tax benefit 1.00%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 1.00%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 1.00%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Employee share-based compensation 1.00%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost   2.00%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost
Intercompany profit (1.00%)nati_EffectiveIncomeTaxRateReconciliationIntercompanyProfit (2.00%)nati_EffectiveIncomeTaxRateReconciliationIntercompanyProfit 2.00%nati_EffectiveIncomeTaxRateReconciliationIntercompanyProfit
Nondeductible acquisition costs     2.00%nati_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseAcquisitionCosts
Domestic production activities deduction (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities  
Decrease in unrecognized tax benefits (10.00%)nati_EffectiveIncomeTaxRateReconciliationUnrecognizedTaxBenefits    
Other (1.00%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 2.00%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments  
Effective tax rate 12.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 17.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 22.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations