Document and Entity Information [Abstract] Entity Central Index Key Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Period Focus Amendment Flag Document Type Document Quarterly Report Document Transition Report Entity Ex Transition Period Document Period End Date Entity File Number Entity Registrant Name Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Three Entity Address, City or Town Entity Address, State or Province Entity Address, Postal Zip Code City Area Code Local Phone Number Title of 12(b) Security Trading Symbol Name of Exchange on which Security is Registered Entity Current Reporting Status Entity Interactive Data Current Entity Filer Category Entity Small Business Entity Emerging Growth Company Entity Shell Company Entity Common Stock, Shares Outstanding Statement of Financial Position [Abstract] Assets: Cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Fixed income securities, at fair value Available-for-sale Securities, Debt Securities, Estimated Fair Value Total fixed income securities Equity securities, at fair value Total equity securities Other investments Total cash and investments Investments and Cash Premiums and agents' balances receivable Deferred policy acquisition costs Balance, beginning of period Balance, end of period Reinsurance recoverables on losses Reinsurance recoverables Income tax recoverables Accrued investment income Property and equipment Total property and equipment, net Receivable from Federal Crop Insurance Corporation Goodwill and other intangibles Other assets Total assets Assets Liabilities: Unpaid losses and loss adjustment expenses Unpaid losses and LAE Unearned premiums Reinsurance premiums payable Reinsurance premiums payable. Income tax payable Deferred income taxes, net Accrued expenses and other liabilities Commitments and Contingencies Total liabilities Liabilities Shareholders' equity: Equity: Common stock, $0.01 par value, authorized: 25,000,000 shares; issued: 23,000,000 shares; and outstanding: 2020 - 21,346,079 shares, 2019 - 22,119,380 shares Preferred stock, without par value, authorized 5,000,000 shares, no shares issued or outstanding Additional paid-in capital Unearned employee stock ownership plan shares Unearned ESOP Shares Retained earnings Accumulated other comprehensive income, net of income taxes Treasury stock, at cost, 2020 - 1,486,866 shares, 2019 - 713,565 shares Treasury Stock, Value Non-controlling interest Total shareholders' equity Balance Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and shareholders' equity Liabilities and Equity Common stock, par value Common stock, shares authorized Common stock, shares issued Common stock, shares outstanding Net common shares outstanding Preferred stock, shares authorized Preferred stock, shares issued Preferred stock, shares outstanding Treasury stock, shares Income Statement [Abstract] Revenues: Net premiums earned Net premiums Fee and other income Net investment income Net capital gain on investments Net capital gain (loss) on investments Total revenues Revenue contribution Expenses: Losses and loss adjustment expenses Net losses and loss adjustment expenses Net losses and LAE Amortization of deferred policy acquisition costs Other underwriting and general expenses Total expenses Operating Expenses Income (loss) before income taxes Income (loss) before income taxes Income tax expense (benefit) Income taxes Net income (loss) Net income (loss) Net income Net Income Net income attributable to non-controlling interest Net income (loss) attributable to non-controlling interest Net income (loss) attributable to NI Holdings, Inc. Net income (loss) attributable to NI Holdings, Inc. Net Income attributable to NI Holdings, Inc. Basic earnings (loss) per common share Diluted earnings (loss) per common share Statement [Table] Statement, Equity Components [Axis] Equity Components [Axis] Attributable to NI Holdings, [Member] Attributable to Non-Controlling Interest [Member] Statement [Line Items] Other comprehensive income, before income taxes: Holding gains on investments Reclassification adjustment for net realized capital (gain) loss included in net income Other comprehensive income, before income taxes Income tax expense related to items of other comprehensive income Income tax expense related to items of other comprehensive income. Other comprehensive income, net of income taxes Comprehensive income (loss) Common Stock [Member] Additional Paid-in Capital [Member] Unearned Employee Stock Ownership Plan Shares [Member] Unearned Employee Stock Ownership Plan Shares [Member] Retained Earnings [Member] Accumulated Other Comprehensive Income, Net of Income Taxes [Member] Treasury Stock [Member] Treasury Stock Non-controlling Interest [Member] Cumulative effect of change in accounting for equity securities Cumulative effect of change in accounting for equity securities. Other comprehensive income, net of income taxes Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Purchase of treasury stock Shares repurchased, value Share-based compensation Issuance of vested award shares Issuance of common stock Reclassification of tax effects stranded in AOCI from tax reform Distribution of employee stock ownership plan shares Shares Held in Employee Stock Option Plan, Allocated Statement of Cash Flows [Abstract] Cash Flows from Operating Activities: Adjustments to reconcile net income to net cash flows from operating activities: Net capital gain on investments Gain (Loss) on Investments, Excluding Other than Temporary Impairments Deferred income tax (benefit) expense Increase (Decrease) in Deferred Income Taxes Depreciation of property and equipment The amount of depreciation or (credit) during the period for property, plant and equipment. Amortization of intangibles Share-based compensation Share-based Payment Arrangement, Noncash Expense Amortization of deferred policy acquisition costs Amortization of deferred policy acquisition costs Deferred Policy Acquisition Costs, Amortization Expense Deferral of policy acquisition costs Deferral of policy acquisition costs Net amortization of premiums and discounts on investments Accretion (Amortization) of Discounts and Premiums, Investments Loss on sale of property and equipment Gain (Loss) on Disposition of Property Plant Equipment Changes in operating assets and liabilities: Premiums and agents' balances receivable Increase (Decrease) in Other Receivables Reinsurance premiums receivable / payable Increase (Decrease) in Reinsurance Recoverable Reinsurance recoverables on losses Reinsurance recoverables on losses. Surplus Notes Two [Member] Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Receivable from Federal Crop Insurance Corporation Increase decrease in Reinsurance receivables. Other Long Term Investment [Member] Income tax recoverable / payable Increase (Decrease) in Income Taxes Receivable Other assets Increase (Decrease) in Other Operating Assets Unpaid losses and loss adjustment expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Unearned premiums Increase (Decrease) in Unearned Premiums Accrued expenses and other liabilities Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Net cash flows from operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Proceeds from maturities and sales of fixed income securities Proceeds from sales of equity securities Purchases of fixed income securities Payments to Acquire Debt Securities, Available-for-sale Purchases of equity securities Payments to Acquire Available-for-sale Securities, Equity Purchases of property and equipment, net Payments to Acquire Property, Plant, and Equipment Acquisition of Westminster American Insurance Company (cash consideration paid net of cash and cash equivalents acquired) Payments to Acquire Businesses, Net of Cash Acquired Other Payments for (Proceeds from) Other Investing Activities Net cash flows from investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Purchases of treasury stock Payments for Repurchase of Equity Issuance of restricted stock awards Net cash flows from financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Non-cash item: Present value of installment payable issued in connection with acquisition of Westminster American Insurance Company Present value of installment payable issued in connection with acquisition of Westminster American Insurance Company. Income taxes paid Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization Basis of Presentation Accounting Policies [Abstract] Summary of Significant Accounting Policies Business Combinations [Abstract] Acquisition of Westminster American Insurance Company Recent Accounting Pronouncements Marketable Securities [Abstract] Investments [Abstract] Investments Investments, All Other Investments [Abstract] Fair Value Measurements Reinsurance Disclosures [Abstract] Reinsurance Deferred Policy Acquisition Costs Disclosures [Abstract] Deferred Policy Acquisition Costs Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract] Unpaid Losses and Loss Adjustment Expenses Property, Plant and Equipment [Abstract] Property and Equipment Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Other Intangibles Related Party Transactions [Abstract] Related Party Transactions Compensation Related Costs [Abstract] Benefit Plans Debt Disclosure [Abstract] Line of Credit Income Tax Disclosure [Abstract] Income Taxes