2.2.0.25falsefalse0120 - Statement - Consolidated Statements of Income (Unaudited)truefalseIn Thousands, except Per Share datafalse1falsefalseUSDfalsefalse1/1/2011 - 3/31/2011 USD ($) USD ($) / shares $Jan-01-2011_Mar-31-2011http://www.sec.gov/CIK0000793547duration2011-01-01T00:00:002011-03-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDEPSDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$2falsefalseUSDfalsefalse1/1/2010 - 3/31/2010 USD ($) USD ($) / shares $ThreeMonthsEnded_31Mar2010http://www.sec.gov/CIK0000793547duration2010-01-01T00:00:002010-03-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDEPSDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$2true0us-gaap_IncomeStatementAbstractus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseConsolidated Statements of Income [Abstract]3false0navg_GrossWrittenPremiumsnavgfalsecreditdurationGross written premiums.falsefalsefalsefalsefalsefalsefalsefalsefalsefalsetotallabel1truefalsefalse296283000296283falsetruefalsefalsefalse2truefalsefalse270145000270145falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryGross written premiums.No authoritative reference available.truefalseGross written premiums4true0us-gaap_RevenuesAbstractus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseRevenues:5false0us-gaap_PremiumsWrittenNetus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse193076000193076falsefalsefalsefalsefalse2truefalsefalse189317000189317falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryPremiums written for all insurance and reinsurance contracts, after adding premiums assumed from other insurers and subtracting any amounts ceded to another insurer.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 17 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 27 -Subparagraph a, b falsefalseNet written premiums6false0navg_DecreaseIncreaseInUnearnedPremiumsnavgfalsecreditdurationDecrease (increase) in unearned premiums.falsefalsefalsefalsefalsefalsefalsefalsefalsefalsetotallabel1truefalsefalse-40598000-40598falsefalsefalsefalsefalse2truefalsefalse-25248000-25248falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryDecrease (increase) in unearned premiums.No authoritative reference available.truefalseChange in unearned premiums7false0us-gaap_PremiumsEarnedNetus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse152478000152478falsefalsefalsefalsefalse2truefalsefalse164069000164069falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryPremiums earned on the income statement for all insurance and reinsurance contracts after subtracting any amounts ceded to another insurer and adding premiums assumed from other insurers.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 1 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 27 -Subparagraph a, b falsefalseNet earned premiums8false0us-gaap_NetInvestmentIncomeus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse1738400017384falsefalsefalsefalsefalse2truefalsefalse1797200017972falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe income earned from investments in securities and property, equipment and other capital assets. 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