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Fair Value Measurement of Assets and Liabilities - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Foreign currency exchange forward contracts outstanding | $ 0 nvtl_ForeignCurrencyExchangeForwardContractsOutstanding | $ 0 nvtl_ForeignCurrencyExchangeForwardContractsOutstanding |
Foreign currency losses on foreign currency denominated transactions | $ 176,000 us-gaap_ForeignCurrencyTransactionGainLossBeforeTax | $ 183,000 us-gaap_ForeignCurrencyTransactionGainLossBeforeTax | $ 51,000 us-gaap_ForeignCurrencyTransactionGainLossBeforeTax

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- Definition Foreign currency exchange forward contracts outstanding. + References No definition available. + Details
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Namespace Prefix: | nvtl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30700-110894 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration