Income Statement [Abstract] Revenues: Revenues [Abstract] Earned premium Premiums Earned, Net, Property and Casualty Percent change, Earned premium Increase Decrease in Premiums Earned, Net, Property And Casualty Increase Decrease in Premiums Earned, Net, Property And Casualty Installment and other fee income ipcc_InstallmentandOtherFeeIncome Installment and other fees collected from policyholders. Percent change, Installment and other fee income Increase Decrease Installment and Other Fee Income Increase Decrease Installment and Other Fee Income Net investment income Net Investment Income Percent change, Net investment Income Increase Decrease in Net Investment Income Increase Decrease in Net Investment Income Total net realized (losses) gains on investments Realized Investment Gains (Losses) Percent change, Net realized gains on investments Increase Decrease Realized Investment Gains Losses Increase Decrease Realized Investment Gains Losses Other income Other Income Percent change, Other income Increase Decrease in Other Income Increase Decrease in Other Income Total revenues Revenues Percent change, Total revenues Increase Decrease in Revenues Increase Decrease in Revenues Costs and Expenses: Costs and Expenses [Abstract] Losses and loss adjustment expenses Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability Percent change, Losses and loss adjustment expenses Increase Decrease in Incurred Claims Property Casualty And Liability Increase Decrease in Incurred Claims Property Casualty And Liability Commissions and other underwriting expenses Commissions and Other Underwriting Expenses Commission expense incurred to persons or entities for generating or placing insurance policies with the company, determined as percentage of policy premiums, as well as costs incurred during the period, such as those relating to general administration and policy maintenance, that do not vary with and are not primarily related to the acquisition or renewal of insurance contracts. Percent change, Commissions and other underwriting expenses Increase Decrease in Commissions And Other Underwriting Expenses Increase Decrease in Commissions And Other Underwritting Expenses Interest expense Interest Expense Percent change, Interest expense Increase Decrease in Interest Expense Increase Decrease in Interest Expense Corporate general and administrative expenses General and Administrative Expense Percent change, Corporate general and administrative expenses Increase Decrease in General and Administrative Expense Increase Decrease in General and Administrative Expense Other expenses Other Cost and Expense, Operating Percent change, Other expenses Increase Decrease in Other Cost and Expense Operating Increase Decrease in Other Cost and Expense Operating Total costs and expenses Benefits, Losses and Expenses Percent change, Total costs and expenses Increase Decrease in Benefits Losses and Expenses Increase Decrease in Benefits Losses and Expenses Earnings before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Percent change, Earnings before income taxes Increase Decrease in Income Loss from Continuing Operations Before Income Taxes Minority Interest and Inome Loss from Equity Method Investments Increase Decrease in Income Loss from Continuing Operations Before Income Taxes Minority Interest and Inome Loss from Equity Method Investments Income Taxes Provision for income taxes Income Tax Expense (Benefit) Percent change, Provision for income taxes Increase Decrease in Income Tax Expense Benefit Increase Decrease in Income Tax Expense Benefit Net Earnings Net Income (Loss) Attributable to Parent Percent change, Net Earnings Increase Decrease in Net Income Loss Increase Decrease in Net Income Loss Net Earnings per Common Share: Earnings Per Share [Abstract] Basic (usd per share) Earnings Per Share, Basic Percent change, Basic Earnings, Basic, Percentage Change Earnings, Basic, Percentage Change Diluted (usd per share) Earnings Per Share, Diluted Percent change, Diluted Earnings, Diluted, Percentage Change Earnings, Diluted, Percentage Change Average Number of Common Shares: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (shares) Weighted Average Number of Shares Outstanding, Basic Percent change, Basic Increase Decrease in Weighted Average Number of Shares Outstanding Basic Increase Decrease in Weighted Average Number of Shares Outstanding Basic Diluted (shares) Weighted Average Number of Shares Outstanding, Diluted Percent change, Diluted Increase Decrease in Weighted Average Number of Diluted Shares Outstanding Increase Decrease in Weighted Average Number of Diluted Shares Outstanding Cash Dividends per Common Share (usd per share) Common Stock, Dividends, Per Share, Cash Paid Percent change, Cash Dividends per Common Share Common Stock, Dividends, Cash Paid, Percentage Change Common Stock, Dividends, Cash Paid, Percentage Change Net realized gains on sales Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Trading Securities, Change in Unrealized Holding Gain (Loss) Trading Securities, Change in Unrealized Holding Gain (Loss) Total other-than-temporary impairment (OTTI) losses Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Non-credit portion in other comprehensive income Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities Non-credit portion in other comprehensive income, percent Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities, Percent Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities, Percent OTTI losses reclassified from other comprehensive income Impairment Loss Reclassified From Other Comprehensive Income To Earnings Other-than-temporary impairment losses reclassed from other comprehensive income to earnings. Net impairment losses recognized in earnings Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities Total net realized (losses) gains on investments Percent change, Total net realized gains on investments Fair Value Disclosures [Abstract] Fair Value Fair Value Disclosures [Text Block] Supplemental Cash Flow Elements [Abstract] Additional Information Additional Financial Information Disclosure [Text Block] Investments, Debt and Equity Securities [Abstract] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Investments by Unrealized Gain or Loss Position [Axis] Investments by Unrealized Gain or Loss Position [Axis] Investments by Unrealized Gain or Loss Position [Axis] Investments by Unrealized Gain or Loss Position [Domain] Investments by Unrealized Gain or Loss Position [Domain] Investments by Unrealized Gain or Loss Position [Domain] Securities with Unrealized Gains Securities with Unrealized Gains [Member] Securities with Unrealized Gains [Member] Securities with Unrealized Losses Securities with Unrealized Losses [Member] Securities with Unrealized Losses [Member] Securities with No Unrealized Gains or Losses Securities with No Unrealized Gains or Losses [Member] Securities with No Unrealized Gains or Losses [Member] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] One year or less, fair value Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value One year or less, amortized cost Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis After one year through five years, fair value Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value After one year through five years, amortized cost Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis After five years through ten years, fair value Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value After five years through ten years, amortized cost Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis After ten years, fair value Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value After ten years, amortized cost basis Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Mortgage-backed, asset-backed and collateralized mortgage obligations, fair value Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value Mortgage-backed, asset-backed and collateralized mortgage obligations, amortized cost Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis Fair Value, Fixed maturities Available-for-sale Securities, Debt Securities Amortized Cost, Fixed Maturities Available-for-sale Debt Securities, Amortized Cost Basis Accounting Policies [Abstract] Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] As Reported Scenario, Previously Reported [Member] As Adjusted Restatement Adjustment [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Agents' balances and premium receivable Premiums and Other Receivables, Net Current and deferred income taxes Deferred Tax Assets, Net of Valuation Allowance Total assets Assets Other liabilities Other Liabilities Shareholders' equity Stockholders' Equity Attributable to Parent Total liabilities and shareholders' equity Liabilities and Equity Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Document Information [Abstract] Document Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Personal Auto Personal Auto Segment [Member] Personal Auto Segment [Member] Commercial Vehicle Commercial Vehicle Segment [Member] Commercial Vehicle Segment [Member] Classic Collector Classic Collector Segment [Member] Classic Collector Segment [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Gross written premium Reinsurance Premiums for Insurance Companies, Direct Written Premium, Gross Amount Including Reinsurance Assumed Reinsurance Premiums for Insurance Companies, Direct Written Premium, Gross Amount Including Reinsurance Assumed Ceded reinsurance Reinsurance Premiums for Insurance Companies, Direct Written Premium, Amount Ceded to Other Companies Reinsurance Premiums for Insurance Companies, Direct Written Premium, Amount Ceded to Other Companies Net written premium Reinsurance Premiums for Insurance Companies, Direct Written Premium, Net Amount Reinsurance Premiums for Insurance Companies, Direct Written Premium, Net Amount Change in unearned premium Reinsurance Premiums for Insurance Companies, Direct Written Premium, Net Amount Increase (Decrease) Reinsurance Premiums for Insurance Companies, Direct Written Premium, Net Amount Increase (Decrease) Earned premium Premiums Earned, Net Net realized gains on investments Segment Information Segment Reporting Disclosure [Text Block] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Equity Award [Domain] Restricted stock not vested Restricted Stock [Member] Dilutive effect of Performance Share Plan Performance Shares [Member] Computation of net earnings per share Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Net earnings Average basic shares outstanding (shares) Basic net earnings per share (usd per share) Dilutive shares (shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Average diluted shares outstanding (shares) Diluted net earnings per share (usd per share) Insurance [Abstract] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Unpaid losses on known claims, balance at beginning of period Liability for Unpaid Claims, Reported Claims, Property and Casualty, Amount Liability for Unpaid Claims, Reported Claims, Property and Casualty, Amount IBNR losses, balance at beginning of period Liability for Unpaid Claims, Incurred but Not Reported Claims (IBNR), Property and Casualty, Amount Liability for Unpaid Claims, Incurred but Not Reported Claims (IBNR), Property and Casualty, Amount LAE, balance at beginning of period Liability for Claims Adjustment Expense, Property and Casualty, Amount Liability for Claims Adjustment Expense, Property and Casualty, Amount Total unpaid losses and LAE, balance at beginning of period Liability for Claims and Claims Adjustment Expense, Property Casualty Liability Reinsurance recoverables, balance at beginning of period Reinsurance Recoverables, Excluding Paid Losses Recoverables Reinsurance Recoverables, Excluding Paid Losses Recoverable Unpaid losses and LAE, net of reinsurance recoverables, balance at beginning of period Liability for Claims and Claims Adjustment Expense, Excluding Reinsurance Recoverables, Property Casualty Liability Liability for Claims and Claims Adjustment Expense, Excluding Reinsurance Recoverables, Property Casualty Liability Loss and LAE incurred, current accident year Current Year Claims and Claims Adjustment Expense Loss and LAE incurred, Prior accident years Prior Year Claims and Claims Adjustment Expense Total loss and LAE incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Loss and LAE payments, current accident year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Loss and LAE payments, prior accident years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total loss and LAE payments Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Unpaid losses and LAE, net of reinsurance recoverables, balance at end of period Add back reinsurance recoverables, balance at end of period Total unpaid losses and LAE, balance at end of period Unpaid losses on known claims, balance at end of period IBNR losses, balance at end of period LAE, balance at end of period Summary of information of investment portfolio Unrealized Gain (Loss) on Investments [Table Text Block] Unrealized loss by investment category and length of time Schedule of Unrealized Loss on Investments [Table Text Block] Summary of unrealized gains or losses Summary of Unrealized Gains and Losses on Investments [Table Text Block] Summary of Unrealized Gains and Losses on Investments [Table Text Block] Unrealized loss by age and severity Unrealized Loss on Investments by Age and Severity [Table Text Block] Unrealized Loss on Investments by Age and Severity [Table Text Block] Change in unrealized gains (losses) on marketable securities Schedule of Changes in Unrealized Gains (Losses) on Investments [Table Text Block] Schedule of Changes in Unrealized Gains (Losses) on Investments [Table Text Block] Progression of credit losses on fixed maturity securities Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table Text Block] Scheduled maturities of fixed maturity securities Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Kemper Corporation Kemper Corporation [Member] Kemper Corporation [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Transaction value Business Combination, Consideration Transferred Weighted average share price (usd per share) Business Acquisition, Weighted Average Share Price Business Acquisition, Weighted Average Share Price Share price (usd per share) Share Price Business acquisition, share price (usd per share) Business Acquisition, Share Price Entity Number of Employees Entity Number of Employees Cash, mixed consideration (use per share) Business Acquisition, Cash Per Share, Mixed Consideration Business Acquisition, Cash Per Share, Mixed Consideration Stock, mixed consideration (shares) Business Acquisition, Stock Redemption, Shares, Mixed Consideration Business Acquisition, Stock Redemption, Shares, Mixed Consideration Cash, cash consideration (usd per share) Business Acquisition, Cash Per Share, Cash Consideration Business Acquisition, Cash Per Share, Cash Consideration Stock, stock consideration (shares) Business Acquisition, Stock Redemption, Shares, Stock Consideration Business Acquisition, Stock Redemption, Shares, Stock Consideration Percentage of ownership Business Acquisition, Percentage of Voting Interests Acquired Number of positions held with unrealized gains (positions) Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Number of Positions Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Number of Positions Number of positions held with unrealized losses (positions) Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Number of positions held that individually exceed unrealized gains of $500,000 (positions) Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Number of Positions With Unrealized Gains Over Five Hundred Thousand Dollars Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Number of Positions With Unrealized Gains Over Five Hundred Thousand Dollars Number of positions held that individually exceed unrealized losses of $500,000 (positions) Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions With Unrealized Losses Over Five Hundred Thousand Dollars Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions With Unrealized Losses Over Five Hundred Thousand Dollars Percentage of positions held with unrealized gains that were investment grade (percent) Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Percentage of Positions That Were Investment Grade Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Percentage of Positions That Were Investment Grade Percentage of positions held with unrealized losses that were investment grade (percent) Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage of Positions That Were Investment Grade Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage of Positions That Were Investment Grade Percentage of fair value held with unrealized gains that were investment grade (percent) Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Percentage of Fair Value Held That Were Investment Grade Positions Available-for-sale, Securities in Unrealized Gain Positions, Qualitative Disclosure, Percentage of Fair Value Held That Were Investment Grade Positions Percentage of fair value held with unrealized losses that were investment grade (percent) Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage of Fair Value Held That Were Investment Grade Positions Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage of Fair Value Held That Were Investment Grade Positions Credit losses on fixed maturity securities Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Beginning balance Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Percent change, Net realized gains on sales Increase Decrease in Avaiable for Sale Securities Gross Realized Gain Loss Excluding Other than Temporary Impairments Increase Decrease in Avaiable for Sale Securities Gross Realized Gain Loss Excluding Other than Temporary Impairments Additions for: Previously impaired securities Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses Additions for: Newly impaired securities Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment Reductions for: Securities sold and paid down Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold Ending balance Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Computation of Basic and Diluted Net Earnings Per Common Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Computation of Net Earnings per Share Earnings Per Share [Text Block] Liability for unpaid losses and LAE Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Statement of Financial Position [Abstract] Fixed maturities, amortized cost Equity securities, cost Available-for-sale Equity Securities, Amortized Cost Basis Short term investments, amortized cost Available-for-sale Securities, Amortized Cost Basis, Short-term Available-for-sale Securities, Amortized Cost Basis, Short-term Agents' balances and premium receivable, allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Property and equipment, accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Recoverable from reinsurers, paid losses and loss adjustment expenses Reinsurance Recoverable for Paid Claims and Claims Adjustments Long-term debt, fair value Long-term Debt, Fair Value Common stock, par value (usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (shares) Common Stock, Shares Authorized Common stock, shares issued (shares) Common Stock, Shares, Issued Treasury stock, shares (shares) Treasury Stock, Shares Stockholders' Equity Note [Abstract] Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Change Post-retirement Benefit Liability Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Unrealized Gains on Investments, Net and Other-than-Temporary Impairments Accumulated Net Unrealized Gain (Loss) and Other-than-Temporary Impairment [Member] Accumulated Net Unrealized Gain (Loss) and Other-than-Temporary Impairment [Member] Reclassification Adjustment for Other-than-Temporary Impairments Accumulated Other-than-Temporary Impairment Attributable to Parent [Member] Accumulated Unrealized Gains on Investments, Net Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Before Tax [Abstract] Other Comprehensive Income (Loss), before Tax [Abstract] Accumulated other comprehensive income, beginning of period AOCI Including Portion Attributable to Noncontrolling Interest, before Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Before Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Before Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Before Tax Other comprehensive income (loss) before reclassification Other Comprehensive Income (Loss), before Reclassifications, before Tax Reclassicification adjustment Reclassicification from Accumulated Other Comprehensive Income, Current Period, Before Tax Reclassicification from Accumulated Other Comprehensive Income, Current Period, Before Tax Effect on other comprehensive income Other Comprehensive Income (Loss), before Tax Effect on other comprehensive income, including cumulative effect of change in accounting principle Other Comprehensive Income (Loss), before Tax, Including Cumulative Effect of Change in Accounting Principle Other Comprehensive Income (Loss), before Tax, Including Cumulative Effect of Change in Accounting Principle Accumulated other comprehensive income, end of period Income Tax [Abstract] Other Comprehensive Income (Loss), Tax [Abstract] Accumulated other comprehensive income, beginning of period Accumulated Other Comprehensive Income (Loss), Tax Accumulated Other Comprehensive Income (Loss), Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Tax Other comprehensive income (loss) before reclassification Other Comprehensive Income (Loss) before Reclassifications, Tax Reclassification adjustment Reclassicification from Accumulated Other Comprehensive Income, Current Period, Tax Reclassicification from Accumulated Other Comprehensive Income, Current Period, Tax Effect on other comprehensive income Other Comprehensive Income (Loss), Tax Effect on other comprehensive income, including cumulative effect of change in accounting principle Other Comprehensive Income (Loss), Tax, Including Effect of Change in Accounting Principle Other Comprehensive Income (Loss), Tax, Including Effect of Change in Accounting Principle Accumulated other comprehensive income, end of period Net [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated other comprehensive income, beginning of period Accumulated Other Comprehensive Income (Loss), Net of Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Net of Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Net of Tax Cumulative Effect of New Accounting Principle in Period of Adoption, Net of Tax Other comprehensive income (loss) before reclassification Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassicification adjustment Reclassicification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassicification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Other comprehensive (loss) income, net of tax Other Comprehensive Income (Loss), Net of Tax Effect on other comprehensive income, including cumulative effect of change in accounting principle Other Comprehensive Income (Loss), Net of Tax, Including Effect of Change in Accounting Principle Other Comprehensive Income (Loss), Net of Tax, Including Effect of Change in Accounting Principle Accumulated other comprehensive income, end of period Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring basis Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Fixed Maturities Debt Securities [Member] U.S. government US Government Debt Securities [Member] State and Municipal US States and Political Subdivisions Debt Securities [Member] Mortgage- Backed Securities Collateralized Mortgage Backed Securities [Member] Residential Residential Mortgage Backed Securities [Member] Commercial Commercial Mortgage Backed Securities [Member] Asset-backed securities Asset-backed Securities, Securitized Loans and Receivables [Member] Corporates Corporate Debt Securities [Member] Equity securities Equity Securities [Member] Short-term investments Short-term Investments [Member] Fair Value, Assets and Liabilities Measured on Recurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Available-for-sale securities: Available-for-sale Securities Total cash and investments Assets, Fair Value Disclosure Percentage of total cash and investments (percent) Fair Value Disclosure, Percentage Fair Value Disclosure, Percentage of Total Long-term debt Notes Payable, Fair Value Disclosure Supplemental Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Proceeds from sale of available-for-sale securities Proceeds from Sale of Available-for-sale Securities Receivable for securities sold Receivable for Investments Sold Receivable For Investments Sold Gross realized gains Available-for-sale Securities, Gross Realized Gains Gross realized losses Available-for-sale Securities, Gross Realized Losses Age of Unrealized Loss [Axis] Age of Unrealized Loss [Axis] Age of Unrealized Loss [Axis] Age of Unrealized Loss [Domain] Age of Unrealized Loss [Domain] Age of Unrealized Loss [Domain] Less than 12 Months Less Than Twelve Months [Member] Less Than 12 Months [Member] 12 Months or More 12 Months or more [Member] 12 Months or more [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Minimum Minimum [Member] Number of Securities with Unrealized Losses (positions) Less than 12 Months, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Less than 12 Months, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Unrealized Losses as Percentage of Cost Unrealized Losses as Percentage of Cost Unrealized Losses as Percentage of Cost 12 Months or More, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 12 Months of More, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Percentage of book value (percent) Threshold for Impairment Evaluation, Percentage of Book Value Threshold for Impairment Evaluation, Percentage of Book Value Unrealized loss amount Threshold for Impairment Evaluation, Unrealized Loss Amount Threshold for Impairment Evaluation, Unrealized Loss Amount Debt Disclosure [Abstract] Schedule of long-term debt Schedule of Long-term Debt Instruments [Table Text Block] Severity of Unrealized Loss [Axis] Severity of Unrealized Loss [Axis] Severity of Unrealized Loss [Axis] Severity of Unrealized Loss [Domain] Severity of Unrealized Loss [Domain] Severity of Unrealized Loss [Domain] Less Than 5% as a Percentage of Amortized Cost or Cost Less Than Five Percent as a Percentage of Amortized Cost or Cost [Member] Less Than Five Percent as a Percentage of Amortized Cost or Cost [Member] 5% - 10% as a Percentage of Amortized Cost or Cost Between Five Percent and Ten Percent as a Percentage of Amortized Cost or Cost [Member] Between Five Percent and Ten Percent as a Percentage of Amortized Cost or Cost [Member] Greater Than 10% as a Percentage of Amortized Cost or Cost Greater Than Ten Percent as a Percentage of Amortized Cost or Cost [Member] Greater Than Ten Percent as a Percentage of Amortized Cost or Cost [Member] Three months or less Zero To Three Months [Member] Zero To Three Months [Member] Four months through six months Three To Six Months [Member] Three To Six Months [Member] Seven months through nine months Six To Nine Months [Member] Six To Nine Months [Member] Ten months through twelve months Nine To Twelve Months [Member] Nine To Twelve Months [Member] Greater than twelve months Greater Than Twelve Months [Member] Greater Than Twelve Months [Member] Fair Value of Securities with Unrealized Losses Fair Value of Securities with Unrealized Losses Fair Value of Securities with Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Total Gross Unrealized Losses Total Gross Unrealized Losses Total Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Long-Term Debt Long-term Debt [Text Block] Reconciliation of provision for income taxes Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Favorable reserve development related to prior accident years Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes Senior Notes [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Senior Notes Due 2022 Senior Notes Due 2022 [Member] Senior Notes Due 2022 [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Principal Debt Instrument, Face Amount Unamortized debt issuance costs Debt Issuance Costs, Net Long-term debt less unamortized debt issuance costs Long-term Debt Schedule of Segment Revenues and Earnings Before Income Taxes Schedule of Segment Reporting Information, by Segment [Table Text Block] Assets Assets [Abstract] Investments: Investments [Abstract] Fixed maturities – at fair value (amortized cost $1,512,939 and $1,439,878) Equity securities – at fair value (cost $65,913 and $68,812) Available-for-sale Securities, Equity Securities Short-term investments – at fair value (amortized cost $0 and $2,541) Short-term Investments Total investments Investments Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accrued investment income Accrued Investment Income Receivable Agents’ balances and premium receivable, net of allowances for doubtful accounts of $13,238 and $15,262 Property and equipment, net of accumulated depreciation of $87,945 and $84,776 Property, Plant and Equipment, Net Prepaid reinsurance premium Prepaid Reinsurance Premiums Recoverables from reinsurers (includes $3,124 and $(1,269) on paid losses and LAE) Reinsurance Recoverables, Including Reinsurance Premium Paid Deferred policy acquisition costs Deferred Policy Acquisition Costs Other assets Other Assets Goodwill Goodwill Total assets Liabilities and Shareholders’ Equity Liabilities and Equity [Abstract] Liabilities: Liabilities [Abstract] Unpaid losses and loss adjustment expenses Unearned premium Unearned Premiums Long-term debt (fair value $286,330 and $290,824) Commissions payable Accrued Sales Commission Payable for securities purchased Payable For Investments Purchased The fair value of purchase transactions of fixed maturity investments available for sale pending settlement. Total liabilities Liabilities Commitments and contingencies (See Note 9) Commitments and Contingencies Shareholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock, no par value (50,000,000 shares authorized; 21,879,505 and 21,867,436 shares issued) Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income, net of tax Treasury stock, at cost (10,937,569 and 10,932,539 shares) Treasury Stock, Value Total shareholders’ equity Total liabilities and shareholders’ equity Unrealized holding gains (losses) on securities arising during the period, pre-tax Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax Unrealized holding gains (losses) on securities arising during the period, tax effects Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized holding gains (losses) on securities arising during period, net of tax Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Realized gains on securities sold, pre-tax Realized gains on securities sold, tax effects Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments, Tax Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments, Tax Realized gains on securities sold, net of tax Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments, Net of Tax Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments, Net of Tax Net impairment losses recognized in earnings Impairment loss recognized in earnings, tax effects Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities, Tax Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities, Tax Impairment loss recognized in earnings Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities, Net of Tax Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities, Net of Tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Change in unrealized gains (losses) on marketable securities, net, net of tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Fair value by hierarchy Fair Value, Assets Measured on Recurring Basis [Table Text Block] Fair value level 3 reconciliation Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Carrying Value and Estimated Fair Value Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Asset Class [Axis] Asset Class [Axis] Fair Value by Asset Class [Domain] Asset Class [Domain] Valuation Technique [Axis] Valuation Technique [Axis] Valuation Technique [Domain] Valuation Technique [Domain] Non-binding broker quotes Non-Binding Broker Quotes [Member] Non-Binding Broker Quotes [Member] Nationally recognized pricing service Nationally Recognized Pricing Service [Member] Nationally Recognized Pricing Service [Member] Fair value level 3 category Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Level 3 reconciliation Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Balance at beginning of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Included in net earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Included in other comprehensive income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Settlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Transfers in Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Balance at end of period Number of positions (securities) Available-for-sale Securities, Number of Positions Available-for-sale Securities, Number of Positions Number of securities purchased and new issues Fair Value, Securities Purchased and New Issues Fair Value, Securities Purchased and New Issues Number of securities, exchange of a rate bond for an unrated refund bond, transfers into level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Number of Securities, Exchange Of A Rate Bond For An Unrated Refund Bond, Transfers Into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Number of Securities, Exchange Of A Rate Bond For An Unrated Refund Bond, Transfers Into Level 3 Number of securities transferred from level 1 to level 2 Fair Value, Liabilities, Number of Securities Transferred From Level 1 to Level 2 Fair Value, Liabilities, Number of Securities Transferred From Level 1 to Level 2 Income tax payments Income Taxes Paid Interest payments on debt Interest Paid Interest payments on capital leases Capital Lease Interest Paid Capital Lease Interest Paid Negative cash book balances Outstanding Checks Outstanding Checks Significant Reporting And Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Statutory accident year underwriting income Statutory Accounting Practices, Statutory Underwriting Income (Loss), Amount Statutory Accounting Practices, Statutory Underwriting Income (Loss), Amount Statutory accident year underwriting income, Combined Ratio Statutory Accounting Practices, Statutory Underwriting Income (Loss), Combined Ratio Statutory Accounting Practices, Statutory Underwriting Income (Loss), Combined Ratio Bad debt charge-offs Premiums Receivable, Allowance for Doubtful Accounts, Write Offs Against Allowance Favorable (unfavorable) development on prior accident years Statutory calendar year underwriting income Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Amount Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Amount Statutory calendar year underwriting income, Combined Ratio Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Combined Ratio Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Combined Ratio Statutory-to-GAAP underwriting income differences Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Differences Statutory Accounting Practices, Statutory To GAAP, Underwriting Income (Loss), Differences GAAP calendar year underwriting income Statutory Accounting Practices, Statutory To GAAP, GAAP Underwriting Income (Loss), Amount Statutory Accounting Practices, Statutory To GAAP, GAAP Underwriting Income (Loss), Amount GAAP calendar year underwriting income, Combined Ratio Statutory Accounting Practices, Statutory To GAAP, GAAP Underwriting Income (Loss), Combined Ratio Statutory Accounting Practices, Statutory To GAAP, GAAP Underwriting Income (Loss), Combined Ratio Interest expense Corporate general and administrative expenses Other expenses Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income, Net of Tax AOCI Attributable to Parent [Member] Treasury Stock Treasury Stock [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance Cumulative effect of change in accounting principle Cumulative Effect of New Accounting Principle in Period of Adoption Net earnings Net change in post-retirement benefit liability Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Change in unrealized gain on investments Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax, Excluding Other Than Temporary Impairment Portion Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax, Excluding Other Than Temporary Impairment Portion Change in non-credit component of impairment losses on fixed maturities Non Credit Portion Of Other Than Temporary Impairments Recognized In Other Comprehensive Income Non-Credit Portion of Other-Than-Temporary Impairments Recognized in Other Comprehensive Income Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Dividends paid to common shareholders Dividends, Common Stock Shares issued and share-based compensation expense Stock Issued During Period Value Value of stock issued during the period as a result of any share-based compensation plan. Acquisition of treasury stock Treasury Stock, Value, Acquired, Par Value Method Ending Balance Total revenues Earnings before income taxes Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Statement of Cash Flows [Abstract] Operating Activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation Depreciation Amortization Accretion (Amortization) of Discounts and Premiums, Investments Net realized gains on investments Loss on disposal of property and equipment Assets Disposed of by Method Other than Sale, in Period of Disposition, Gain (Loss) on Disposition Share-based compensation expense Share-based Compensation Activity related to rabbi trust Non-Cash Activity Related to Rabbi Trust1 Non-Cash Activity Related to Rabbi Trust1 Change in accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Change in agents’ balances and premium receivable Increase (Decrease) in Premiums Receivable Change in reinsurance receivables Increase (Decrease) in Reinsurance Recoverable Change in deferred policy acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs Change in other assets Increase (Decrease) in Other Operating Assets Change in unpaid losses and loss adjustment expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Change in unearned premium Increase (Decrease) in Unearned Premiums Change in other liabilities Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of fixed maturities Payments to Acquire Available-for-sale Securities, Debt Purchases of equity securities Payments to Acquire Available-for-sale Securities, Equity Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Maturities and redemptions of fixed maturities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from sale of fixed maturities Proceeds from Sale of Available-for-sale Securities, Debt Proceeds from sale of equity securities Proceeds from Sale of Available-for-sale Securities, Equity Proceeds from sale of short-term investments Proceeds from Sale of Short-term Investments Proceeds from sale of property and equipment Proceeds from Sale of Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from stock options exercised and employee stock purchases Proceeds from Stock Options Exercised Principal payments under capital lease obligations Repayments of Long-term Capital Lease Obligations Acquisition of treasury stock Payments for Repurchase of Common Stock Dividends paid to shareholders Payments of Ordinary Dividends, Common Stock Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Number of states licensed to write insurance Number of States in which Entity Operates Accounting Standards Update 2018-05 Accounting Standards Update 2018-05 [Member] Accounting Standards Update 2018-05 [Member] Accounting Standards Update 2016-16 Accounting Standards Update 2016-16 [Member] Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Unrealized holding gains on securities arising during period, net of tax Schedule of Other Comprehensive Income Before and After Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Number of operating segments Number of Operating Segments Number of vehicles in fleet in target businesses (or fewer) Number of Vehicles in Fleet in Target Customers Number of Vehicles in Fleet in Target Customers Average vehicles per policy Average Number of Vehicles Per Insurance Policy Average Number of Vehicles Per Insurance Policy Accumulated Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Statement of Comprehensive Income [Abstract] Other comprehensive income before tax: Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] Net change in post-retirement benefit liability Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax Unrealized gains on investments(1): Unrealized Gain (Loss) on Investments [Abstract] Unrealized holding (losses) gains arising during the period Less: Reclassification adjustments for losses (gains) included in net earnings Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax Unrealized (losses) gains on investments, net Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes Other comprehensive (loss) income, before tax Income tax benefit (expense) related to components of other comprehensive income Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract] [Abstract] Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract] [Abstract] Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract] [Abstract] Fixed Maturities Available-for-sale Debt Securities, Amortized Cost Basis [Abstract] Fixed maturities, Gross Unrealized Gains Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax Fixed maturities, Gross Unrealized Losses Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax Fixed maturities, Fair Value Fixed maturities, OTTI Recognized in Accumulated OCI Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities Equity Securities Available-for-sale Equity Securities, Amortized Cost Basis [Abstract] Equity securities, Amortized cost Equity securities, Gross Unrealized Gains Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax Equity securities, Gross Unrealized Losses Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax Equity securities, Fair Value Equity securities, OTTI Recognized in Accumulated OCI Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Equity Securities Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Equity Securities Available-for-sale securities, Amortized Cost or Cost, Total Available-for-sale Securities, Amortized Cost Basis Available-for-sale securities, Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Available-for-sale securities, Gross Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Available-for-sale securities, Fair Value Available-for-sale securities, OTTI Recognized in Accumulated OCI Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale Securities Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale Securities Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Carrying Value Reported Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Total cash and investments Available-for-sale Securities and Cash and Cash Equivalents, Fair Value Disclosure Available-for-sale Securities and Cash and Cash Equivalents, Fair Value Disclosure Insurance Reserves Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] 10-year U.S. Treasury note 10-year U.S. Treasury Note [Member] 10-year U.S. Treasury Note [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] US Treasury Note US Treasury Notes Securities [Member] Coupon rate (percent) Debt Instrument, Interest Rate, Stated Percentage Capitalized debt issuance costs Debt Issuance Costs, Gross Basis points Debt Instrument, Basis Spread on Variable Rate Term of note used (years) Fair Value, Debt Instrument, Valuation Basis, US Treasury Note Rate, Term of Note Used Fair Value, Debt Instrument, Valuation Basis, US Treasury Note Rate, Term of Note Used Effective percentage (percent) Debt Instrument, Interest Rate, Effective Percentage Credit facility capacity Line of Credit Facility, Current Borrowing Capacity Term of revolving credit facility (years) Line of Credit Facility, Term Line of Credit Facility, Term Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Income tax reconciliation Effective Income Tax Rate Reconciliation, Amount [Abstract] Income taxes at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Dividends-received deduction Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount Tax-exempt interest Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Provision for income taxes as shown on the Consolidated Statements of Earnings GAAP effective tax rate (percent) Effective Income Tax Rate Reconciliation, Percent Schedule of Gain (Loss) on Investments [Table] Schedule of Gain (Loss) on Investments [Table] Gain (Loss) on Investments [Line Items] Gain (Loss) on Investments [Line Items] Net losses recognized during the period on equity securities Gain (Loss) on Investments Less: Net gains recognized during the period on equity securities sold Gain (Loss) on Sale of Securities, Net Unrealized losses recognized during the period on equity securities still held at the reporting date Unrealized Gain (Loss) on Securities Basis of Consolidation and Reporting Basis of Accounting, Policy [Policy Text Block] Estimates Use of Estimates, Policy [Policy Text Block] Recently Adopted and Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block]