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Financial Statement Details - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Organization, Consolidation and Presentation of Financial Statements [Abstract] |  |  |
Net unrealized gains (losses) | $ 0 nvtl_AvailableforsaleSecuritiesGrossUnrealizedGainLossAccumulatedInAoci | $ 5,000 nvtl_AvailableforsaleSecuritiesGrossUnrealizedGainLossAccumulatedInAoci |
Property and equipment | 0 us-gaap_ImpairmentOfLongLivedAssetsHeldForUse | 70,000 us-gaap_ImpairmentOfLongLivedAssetsHeldForUse | 100,000 us-gaap_ImpairmentOfLongLivedAssetsHeldForUse
Depreciation and amortization expense | $ 6,300,000 us-gaap_Depreciation | $ 7,900,000 us-gaap_Depreciation | $ 9,400,000 us-gaap_Depreciation

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- Definition Net amount of accumulated unrealized gains (losses) on investments in available-for-sale securities that are recognized in Accumulated Other Comprehensive Income (AOCI). + References No definition available. + Details
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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 958 -SubTopic 225 -Section 45 -Paragraph 11 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28367520&loc=d3e92212-112881 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Impairment -URI http://asc.fasb.org/extlink&oid=6515133 + Details
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