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Nature of Business and Significant Accounting Policies - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Nature Of Business And Significant Accounting Policies [Line Items]                      
Net Income (Loss) Attributable to Parent Before Beneficial Conversion                 $ (39,229,000)nvtl_NetIncomeLossAttributabletoParentBeforeBeneficialConversion $ (43,413,000)nvtl_NetIncomeLossAttributabletoParentBeforeBeneficialConversion $ (89,266,000)nvtl_NetIncomeLossAttributabletoParentBeforeBeneficialConversion
Net loss 4,446,000us-gaap_NetIncomeLoss 8,832,000us-gaap_NetIncomeLoss 17,415,000us-gaap_NetIncomeLoss 8,981,000us-gaap_NetIncomeLoss 21,306,000us-gaap_NetIncomeLoss 5,093,000us-gaap_NetIncomeLoss 7,892,000us-gaap_NetIncomeLoss 9,122,000us-gaap_NetIncomeLoss 39,674,000us-gaap_NetIncomeLoss 43,413,000us-gaap_NetIncomeLoss 89,266,000us-gaap_NetIncomeLoss
Cash, cash equivalents and short-term marketable securities 17,900,000us-gaap_CashCashEquivalentsAndShortTermInvestments               17,900,000us-gaap_CashCashEquivalentsAndShortTermInvestments    
Working capital $ 29,400,000nvtl_WorkingCapital               $ 29,400,000nvtl_WorkingCapital    
Maturity period of cash and cash equivalents                 3 months    
Maturity period of marketable securities                 three months    
Recognized income tax position (percent)                 50.00%nvtl_UncertainTaxPositionRecognitionThreshold    
Developed technologies                      
Nature Of Business And Significant Accounting Policies [Line Items]                      
Period of amortization                 1 year    
Trade name                      
Nature Of Business And Significant Accounting Policies [Line Items]                      
Period of amortization                 3 years    
Minimum                      
Nature Of Business And Significant Accounting Policies [Line Items]                      
Property and equipment useful lives                 18 months    
Period of warranty                 1 year    
Maximum                      
Nature Of Business And Significant Accounting Policies [Line Items]                      
Property and equipment useful lives                 5 years    
Period of warranty                 3 years