2.2.0.25 true Sheet 00 - Document - Document and Entity Information Document and Entity Information http://navg.com/role/DocumentAndEntityInformation false R1.xml false Sheet 0110 - Statement - Consolidated Balance Sheets Consolidated Balance Sheets http://navg.com/role/BalanceSheets false R2.xml false Sheet 0111 - Statement - Consolidated Balance Sheets (Parenthetical) Consolidated Balance Sheets (Parenthetical) http://navg.com/role/BalanceSheetsParenthetical false R3.xml false Sheet 0120 - Statement - Consolidated Statements of Income Consolidated Statements of Income http://navg.com/role/StatementsOfIncome false R4.xml false Sheet 0130 - Statement - Consolidated Statements of Stockholders' Equity Consolidated Statements of Stockholders' Equity http://navg.com/role/StatementsOfStockholdersEquityUnaudited false R5.xml false Sheet 0140 - Statement - Consolidated Statements of Comprehensive Income Consolidated Statements of Comprehensive Income http://navg.com/role/StatementsOfComprehensiveIncomeUnaudited false R6.xml false Sheet 0141 - Statement - Consolidated Statements of Comprehensive Income (Parenthetical) Consolidated Statements of Comprehensive Income (Parenthetical) http://navg.com/role/StatementsOfComprehensiveIncomeUnauditedParenthetical false R7.xml false Sheet 0150 - Statement - Consolidated Statements of Cash Flows Consolidated Statements of Cash Flows http://navg.com/role/StatementsOfCashFlows false R8.xml false Sheet 0201 - Disclosure - Organization and Summary of Significant Accounting Policies Organization and Summary of Significant Accounting Policies http://navg.com/role/OrganizationAndSummaryOfSignificantAccountingPolicies false R9.xml false Sheet 0202 - Disclosure - Earnings Per Share Earnings Per Share http://navg.com/role/EarningsPerShare false R10.xml false Sheet 0203 - Disclosure - Segment Information Segment Information http://navg.com/role/SegmentInformation false R11.xml false Sheet 0204 - Disclosure - Investments Investments http://navg.com/role/Investments false R12.xml false Sheet 0205 - Disclosure - Reserves For Losses And Loss Adjustment Expenses Reserves For Losses And Loss Adjustment Expenses http://navg.com/role/ReservesForLossesAndLossAdjustmentExpenses false R13.xml false Sheet 0206 - Disclosure - Reinsurance Reinsurance http://navg.com/role/Reinsurance false R14.xml false Sheet 0207 - Disclosure - Income Taxes Income Taxes http://navg.com/role/IncomeTaxes false R15.xml false Sheet 0208 - Disclosure - Credit Facility Credit Facility http://navg.com/role/CreditFacility false R16.xml false Sheet 0209 - Disclosure - Senior Note Due May 1, 2016 Senior Note Due May 1, 2016 http://navg.com/role/SeniorNotes false R17.xml false Sheet 0210 - Disclosure - Fiduciary Funds Fiduciary Funds http://navg.com/role/FiduciaryFunds false R18.xml false Sheet 0211 - Disclosure - Commitments and Contingencies Commitments and Contingencies http://navg.com/role/CommitmentsAndContingencies false R19.xml false Sheet 0212 - Disclosure - Share Capital and Share Repurchases Share Capital and Share Repurchases http://navg.com/role/ShareCapitalAndShareRepurchases false R20.xml false Sheet 0213 - Disclosure - Dividends from Subsidiaries and Statutory Financial Information Dividends from Subsidiaries and Statutory Financial Information http://navg.com/role/DividendsFromSubsidiariesAndStatutoryFinancialInformation false R21.xml false Sheet 0214 - Disclosure - Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan http://navg.com/role/StockOptionPlansStockGrantsStockAppreciationRightsAndEmployeeStockPurchasePlan false R22.xml false Sheet 0215 - Disclosure - Retirement Plans Retirement Plans http://navg.com/role/RetirementPlans false R23.xml false Sheet 0216 - Disclosure - Quarterly Financial Data (Unaudited) Quarterly Financial Data (Unaudited) http://navg.com/role/QuarterlyFinancialDataUnaudited false R24.xml false Sheet 0301 - Schedule - Summary of Consolidated Investments other than Investments in Related Parties Summary of Consolidated Investments other than Investments in Related Parties http://navg.com/role/SummaryOfConsolidatedInvestmentsOtherThanInvestmentsInRelatedPartiesSchedule false R25.xml false Sheet 0302 - Schedule - Condensed Financial Information of Registrant Condensed Financial Information of Registrant http://navg.com/role/CondensedFinancialInformationOfRegistrant false R26.xml false Sheet 0303 - Schedule - Supplementary Insurance Information Supplementary Insurance Information http://navg.com/role/SupplementaryInsuranceInformation false R27.xml false Sheet 0304 - Schedule - Reinsurances Reinsurances http://navg.com/role/Reinsurances false R28.xml false Sheet 0305 - Schedule - Valuation and Qualifying Accounts Valuation and Qualifying Accounts http://navg.com/role/ValuationAndQualifyingAccounts false R29.xml false Sheet 0306 - Schedule - Supplementary Information Concerning Property Casualty Insurance Operations Supplementary Information Concerning Property Casualty Insurance Operations http://navg.com/role/SupplementaryInformationConcerningPropertyCasualtyInsuranceOperations false R30.xml false Book All Reports All Reports false 1 64 9 0 3 143 true false BalanceAsOf_31Dec2010_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2009_Treasury_Stock_Member 1 TwelveMonthsEnded_31Dec2010_Treasury_Stock_Member 2 BalanceAsOf_04Feb2011 1 TwelveMonthsEnded_31Dec2010_Additional_Paid_In_Capital_Member 1 TwelveMonthsEnded_31Dec2010_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 TwelveMonthsEnded_31Dec2008 62 BalanceAsOf_31Dec2008_Retained_Earnings_Member 1 TwelveMonthsEnded_31Dec2010_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 TwelveMonthsEnded_31Dec2009_Treasury_Stock_Member 1 BalanceAsOf_31Dec2008_Preferred_Stock_Member 1 TwelveMonthsEnded_31Dec2008_Retained_Earnings_Member 1 TwelveMonthsEnded_31Dec2008_Common_Stock_Member 1 BalanceAsOf_31Dec2008_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 BalanceAsOf_31Dec2009_Additional_Paid_In_Capital_Member 1 BalanceAsOf_31Dec2010 40 BalanceAsOf_31Dec2010_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 BalanceAsOf_31Dec2009_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2009_Preferred_Stock_Member 1 BalanceAsOf_31Dec2010_Additional_Paid_In_Capital_Member 1 Jan-01-2010_Dec-31-2010 97 BalanceAsOf_31Dec2010_Accumulated_Other_Comprehensive_Income_Member 1 BalanceAsOf_31Dec2008_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 BalanceAsOf_31Dec2008_Treasury_Stock_Member 1 TwelveMonthsEnded_31Dec2009_Common_Stock_Member 1 BalanceAsOf_31Dec2007_Treasury_Stock_Member 1 BalanceAsOf_31Dec2010_Common_Stock_Member 1 BalanceAsOf_31Dec2007_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 TwelveMonthsEnded_31Dec2009_Retained_Earnings_Member 1 TwelveMonthsEnded_31Dec2010_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2008_Additional_Paid_In_Capital_Member 1 BalanceAsOf_31Dec2008_Accumulated_Other_Comprehensive_Income_Member 1 BalanceAsOf_30Jun2010 1 BalanceAsOf_31Dec2009_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 BalanceAsOf_31Dec2007_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 BalanceAsOf_30Sep2009_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 TwelveMonthsEnded_31Dec2010_Common_Stock_Member 1 BalanceAsOf_31Dec2007_Preferred_Stock_Member 1 BalanceAsOf_31Dec2007_Retained_Earnings_Member 1 BalanceAsOf_31Dec2010_Treasury_Stock_Member 1 BalanceAsOf_31Dec2007_Additional_Paid_In_Capital_Member 1 TwelveMonthsEnded_31Dec2008_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2009_Common_Stock_Member 1 TwelveMonthsEnded_31Dec2010_Retained_Earnings_Member 1 BalanceAsOf_31Dec2008_Common_Stock_Member 1 BalanceAsOf_31Dec2008_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2008 2 BalanceAsOf_31Dec2010_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 TwelveMonthsEnded_31Dec2008_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 TwelveMonthsEnded_31Dec2009_Additional_Paid_In_Capital_Member 1 TwelveMonthsEnded_31Dec2008_Additional_Paid_In_Capital_Member 1 TwelveMonthsEnded_31Dec2008_Treasury_Stock_Member 1 BalanceAsOf_31Dec2009_Accumulated_Other_Comprehensive_Income_Member 1 TwelveMonthsEnded_31Dec2009_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 TwelveMonthsEnded_31Dec2009_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2010_Retained_Earnings_Member 1 BalanceAsOf_31Dec2007 1 BalanceAsOf_31Dec2009_Non_Credit_Other_Than_Temporary_Impairment_Gains_Losses_Member 1 BalanceAsOf_31Dec2009 40 BalanceAsOf_31Dec2007_Accumulated_Translation_Adjustment_Member 1 BalanceAsOf_31Dec2009_Retained_Earnings_Member 1 BalanceAsOf_31Dec2007_Common_Stock_Member 1 TwelveMonthsEnded_31Dec2009_Accumulated_Net_Unrealized_Investment_Gain_Loss_Member 1 TwelveMonthsEnded_31Dec2009 64 true true