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Securities Purchase Agreement and Warrant Issuances - Additional Information (Detail) (USD $) | 0 Months Ended | 3 Months Ended | 0 Months Ended |
--- | --- | --- | --- | ---
Mar. 26, 2015 | Mar. 31, 2015 | Mar. 31, 2014 | Sep. 08, 2014 | Dec. 31, 2014
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Common stock shares issued at par value (per share) |  | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare |  |  | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare
Proceeds from the exercise of warrant to purchase common stock | $ 8,644,000 us-gaap_ProceedsFromWarrantExercises | $ 8,644,000 us-gaap_ProceedsFromWarrantExercises | $ 0 us-gaap_ProceedsFromWarrantExercises |  |
Series C Preferred Stock |  |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Number of shares sold |  |  |  | 87,196 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesCPreferredStockMember |
Convertible preferred stock par value per share |  |  |  | $ 0.001 us-gaap_TemporaryEquityParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesCPreferredStockMember |
Number of shares sold, Per share price |  |  |  | $ 17.50 us-gaap_SharesIssuedPricePerShare / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesCPreferredStockMember |
Proceeds from the issuances of Series C preferred and common stock, net of issuance costs |  |  |  | 14,400,000 us-gaap_ProceedsFromIssuanceOrSaleOfEquity / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesCPreferredStockMember |
Common Stock |  |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Number of shares sold |  |  |  | 7,363,334 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Common stock shares issued at par value (per share) |  |  |  | $ 0.001 us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Number of shares sold, Per share price |  |  |  | $ 1.75 us-gaap_SharesIssuedPricePerShare / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Common stock warrants outstanding |  |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Warrants to purchase common stock sold (shares) | 1,593,583 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_WarrantMember |  |  | 4,117,647 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_WarrantMember |
Exercise price per share ($ per share) | 5.50 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_WarrantMember |  |  | 2.26 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_WarrantMember |
2014 Warrant | Common stock warrants outstanding |  |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Number of shares sold | 3,824,600 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_ClassOfWarrantOrRightAxis = nvtl_A2014WarrantMember / us-gaap_StatementEquityComponentsAxis = us-gaap_WarrantMember |  |  |  |
2015 Warrant |  |  |  |  |
Changes In Equity And Comprehensive Income Line Items [Line Items] |  |  |  |  |
Proceeds from the exercise of warrant to purchase common stock | $ 3,500,000 us-gaap_ProceedsFromWarrantExercises / us-gaap_ClassOfWarrantOrRightAxis = nvtl_A2015WarrantMember |  |  |  |

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- Definition Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(4)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph i -Subparagraph 4 -Article 4 + Details
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- Definition Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph i -Subparagraph 2 -Article 4 + Details
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- Definition Face amount or stated value per share of common stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 + Details
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- Definition Per share amount of par value or stated value of stock classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 28 -Article 5 + Details
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