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Intangible Assets, Net (Narrative) (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Finite-Lived Intangible Assets [Line Items]    
Total intangible assets amortization expenses $ 8,800,000us-gaap_AmortizationOfIntangibleAssets $ 7,600,000us-gaap_AmortizationOfIntangibleAssets
Capitalized Software Development Costs [Member]    
Finite-Lived Intangible Assets [Line Items]    
Capitalized software development costs 2,300,000us-gaap_CapitalizedComputerSoftwareAdditions
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
8,000,000us-gaap_CapitalizedComputerSoftwareAdditions
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
Capitalized computer software amortization 4,600,000us-gaap_CapitalizedComputerSoftwareAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
3,100,000us-gaap_CapitalizedComputerSoftwareAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
Costs related to stock based compensation $ 95,000nati_CostsRelatedToStockBasedCompensation
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
$ 378,000nati_CostsRelatedToStockBasedCompensation
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_ComputerSoftwareIntangibleAssetMember
Useful life (in years) 3 years  
Minimum [Member] | Acquired Technology [Member]    
Finite-Lived Intangible Assets [Line Items]    
Useful life (in years) 3 years  
Minimum [Member] | Patents [Member]    
Finite-Lived Intangible Assets [Line Items]    
Useful life (in years) 10 years  
Maximum [Member] | Acquired Technology [Member]    
Finite-Lived Intangible Assets [Line Items]    
Useful life (in years) 8 years  
Maximum [Member] | Patents [Member]    
Finite-Lived Intangible Assets [Line Items]    
Useful life (in years) 17 years