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Disclosure - Note 15 - Commitments and Contingencies Sheet http://www.alerus.com/20251231/role/statement-note-15-commitments-and-contingencies Note 15 - Commitments and Contingencies Notes 26 false false R27.htm 995567 - Disclosure - Note 16 - Legal Contingencies Sheet http://www.alerus.com/20251231/role/statement-note-16-legal-contingencies Note 16 - Legal Contingencies Notes 27 false false R28.htm 995568 - Disclosure - Note 17 - Share-based Compensation Plan Sheet http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan Note 17 - Share-based Compensation Plan Notes 28 false false R29.htm 995569 - Disclosure - Note 18 - Employee Benefits Sheet http://www.alerus.com/20251231/role/statement-note-18-employee-benefits Note 18 - Employee Benefits Notes 29 false false R30.htm 995570 - Disclosure - Note 19 - Noninterest Income Sheet http://www.alerus.com/20251231/role/statement-note-19-noninterest-income Note 19 - Noninterest Income Notes 30 false false R31.htm 995571 - Disclosure - Note 20 - Income Taxes Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes Note 20 - Income Taxes Notes 31 false false R32.htm 995572 - Disclosure - Note 21 - Tax Credit Investments Sheet http://www.alerus.com/20251231/role/statement-note-21-tax-credit-investments Note 21 - Tax Credit Investments Notes 32 false false R33.htm 995573 - Disclosure - Note 22 - Segment Reporting Sheet http://www.alerus.com/20251231/role/statement-note-22-segment-reporting- Note 22 - Segment Reporting Notes 33 false false R34.htm 995574 - Disclosure - Note 23 - Earnings Per Share Sheet http://www.alerus.com/20251231/role/statement-note-23-earnings-per-share Note 23 - Earnings Per Share Notes 34 false false R35.htm 995575 - Disclosure - Note 24 - Related Party Transactions Sheet http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions Note 24 - Related Party Transactions Notes 35 false false R36.htm 995576 - Disclosure - Note 25 - Derivative Instruments Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments Note 25 - 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Investment Securities (Tables) Tables http://www.alerus.com/20251231/role/statement-note-5-investment-securities 45 false false R46.htm 995589 - Disclosure - Note 6 - Loans and Allowance for Credit Losses (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-tables Note 6 - Loans and Allowance for Credit Losses (Tables) Tables http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses 46 false false R47.htm 995590 - Disclosure - Note 7 - Land, Premises and Equipment, Net (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-7-land-premises-and-equipment-net-tables Note 7 - Land, Premises and Equipment, Net (Tables) Tables http://www.alerus.com/20251231/role/statement-note-7-land-premises-and-equipment-net 47 false false R48.htm 995591 - Disclosure - Note 8 - Goodwill and Other Intangible Assets (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-tables Note 8 - 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Disclosure - Note 17 - Share-based Compensation Plan (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan-tables Note 17 - Share-based Compensation Plan (Tables) Tables http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan 56 false false R57.htm 995600 - Disclosure - Note 18 - Employee Benefits (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-18-employee-benefits-tables Note 18 - Employee Benefits (Tables) Tables http://www.alerus.com/20251231/role/statement-note-18-employee-benefits 57 false false R58.htm 995601 - Disclosure - Note 19 - Noninterest Income (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-19-noninterest-income-tables Note 19 - Noninterest Income (Tables) Tables http://www.alerus.com/20251231/role/statement-note-19-noninterest-income 58 false false R59.htm 995602 - Disclosure - Note 20 - Income Taxes (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-tables Note 20 - 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Disclosure - Note 24 - Related Party Transactions (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions-tables Note 24 - Related Party Transactions (Tables) Tables http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions 63 false false R64.htm 995607 - Disclosure - Note 25 - Derivative Instruments (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-tables Note 25 - Derivative Instruments (Tables) Tables http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments 64 false false R65.htm 995608 - Disclosure - Note 26 - Regulatory Matters (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-26-regulatory-matters-tables Note 26 - Regulatory Matters (Tables) Tables http://www.alerus.com/20251231/role/statement-note-26-regulatory-matters 65 false false R66.htm 995609 - Disclosure - Note 27 - Other Comprehensive Income (Loss) (Tables) Sheet http://www.alerus.com/20251231/role/statement-note-27-other-comprehensive-income-loss-tables Note 27 - 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Business Combinations - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) Details 72 false false R73.htm 995616 - Disclosure - Note 3 - Business Combinations - Schedule of PCD Financing Receivables (Details) Sheet http://www.alerus.com/20251231/role/statement-note-3-business-combinations-schedule-of-pcd-financing-receivables-details Note 3 - Business Combinations - Schedule of PCD Financing Receivables (Details) Details 73 false false R74.htm 995617 - Disclosure - Note 3 - Business Combinations - Schedule of Business Acquisition, Pro Forma Information (Details) Sheet http://www.alerus.com/20251231/role/statement-note-3-business-combinations-schedule-of-business-acquisition-pro-forma-information-details Note 3 - Business Combinations - Schedule of Business Acquisition, Pro Forma Information (Details) Details 74 false false R75.htm 995618 - Disclosure - Note 4 - Restrictions on Cash and Due from Banks (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-4-restrictions-on-cash-and-due-from-banks-details-textual Note 4 - Restrictions on Cash and Due from Banks (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-4-restrictions-on-cash-and-due-from-banks 75 false false R76.htm 995619 - Disclosure - Note 5 - Investment Securities (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-details-textual Note 5 - Investment Securities (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-5-investment-securities-tables 76 false false R77.htm 995620 - Disclosure - Note 5 - Investment Securities - Schedule of Marketable Securities (Details) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-schedule-of-marketable-securities-details Note 5 - Investment Securities - Schedule of Marketable Securities (Details) Details 77 false false R78.htm 995621 - Disclosure - Note 5 - Investment Securities - Schedule of Realized Gain (Loss) (Details) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-schedule-of-realized-gain-loss-details Note 5 - Investment Securities - Schedule of Realized Gain (Loss) (Details) Details 78 false false R79.htm 995622 - Disclosure - Note 5 - Investment Securities - Schedule of Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value (Details) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-schedule-of-debt-securities-availableforsale-unrealized-loss-position-fair-value-details Note 5 - Investment Securities - Schedule of Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value (Details) Details 79 false false R80.htm 995623 - Disclosure - Note 5 - Investment Securities - Schedule of Investments Classified by Contractual Maturity Date (Details) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-schedule-of-investments-classified-by-contractual-maturity-date-details Note 5 - Investment Securities - Schedule of Investments Classified by Contractual Maturity Date (Details) Details 80 false false R81.htm 995624 - Disclosure - Note 5 - Investment Securities - Schedule of Investments (Details) Sheet http://www.alerus.com/20251231/role/statement-note-5-investment-securities-schedule-of-investments-details Note 5 - Investment Securities - Schedule of Investments (Details) Details 81 false false R82.htm 995625 - Disclosure - Note 6 - Loans and Allowance for Credit Losses (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-details-textual Note 6 - Loans and Allowance for Credit Losses (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-tables 82 false false R83.htm 995626 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Schedule of Total Loans Outstanding by Portfolio Segment (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-schedule-of-total-loans-outstanding-by-portfolio-segment-details Note 6 - Loans and Allowance for Credit Losses - Schedule of Total Loans Outstanding by Portfolio Segment (Details) Details 83 false false R84.htm 995627 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Allowance for Loan Losses by Portfolio Segment (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-allowance-for-loan-losses-by-portfolio-segment-details Note 6 - Loans and Allowance for Credit Losses - Allowance for Loan Losses by Portfolio Segment (Details) Details 84 false false R85.htm 995628 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Schedule of Financing Receivable Credit Quality Indicators (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-schedule-of-financing-receivable-credit-quality-indicators-details Note 6 - Loans and Allowance for Credit Losses - Schedule of Financing Receivable Credit Quality Indicators (Details) Details 85 false false R86.htm 995629 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Schedule of Loans Past Due (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-schedule-of-loans-past-due-details Note 6 - Loans and Allowance for Credit Losses - Schedule of Loans Past Due (Details) Details 86 false false R87.htm 995630 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Schedule of Nonaccrual Loans by Class (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-schedule-of-nonaccrual-loans-by-class-details Note 6 - Loans and Allowance for Credit Losses - Schedule of Nonaccrual Loans by Class (Details) Details 87 false false R88.htm 995631 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Summary of Collateral Types (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-summary-of-collateral-types-details Note 6 - Loans and Allowance for Credit Losses - Summary of Collateral Types (Details) Details 88 false false R89.htm 995632 - Disclosure - Note 6 - Loans and Allowance for Credit Losses - Schedule of Modified Financing Receivables (Details) Sheet http://www.alerus.com/20251231/role/statement-note-6-loans-and-allowance-for-credit-losses-schedule-of-modified-financing-receivables-details Note 6 - Loans and Allowance for Credit Losses - Schedule of Modified Financing Receivables (Details) Details 89 false false R90.htm 995633 - Disclosure - Note 7 - Land, Premises and Equipment, Net (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-7-land-premises-and-equipment-net-details-textual Note 7 - Land, Premises and Equipment, Net (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-7-land-premises-and-equipment-net-tables 90 false false R91.htm 995634 - Disclosure - Note 7 - Land, Premises and Equipment, Net - Schedule of Property, Plant, and Equipment (Details) Sheet http://www.alerus.com/20251231/role/statement-note-7-land-premises-and-equipment-net-schedule-of-property-plant-and-equipment-details Note 7 - Land, Premises and Equipment, Net - Schedule of Property, Plant, and Equipment (Details) Details 91 false false R92.htm 995635 - Disclosure - Note 8 - Goodwill and Other Intangible Assets (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-details-textual Note 8 - Goodwill and Other Intangible Assets (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-tables 92 false false R93.htm 995636 - Disclosure - Note 8 - Goodwill and Other Intangible Assets - Schedule of Goodwill (Details) Sheet http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-schedule-of-goodwill-details Note 8 - Goodwill and Other Intangible Assets - Schedule of Goodwill (Details) Details 93 false false R94.htm 995637 - Disclosure - Note 8 - Goodwill and Other Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details) Sheet http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-schedule-of-finitelived-intangible-assets-details Note 8 - Goodwill and Other Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details) Details 94 false false R95.htm 995638 - Disclosure - Note 8 - Goodwill and Other Intangible Assets - Schedule of Finite-Lived Intangible Assets, Future Amortization Expense (Details) Sheet http://www.alerus.com/20251231/role/statement-note-8-goodwill-and-other-intangible-assets-schedule-of-finitelived-intangible-assets-future-amortization-expense-details Note 8 - Goodwill and Other Intangible Assets - Schedule of Finite-Lived Intangible Assets, Future Amortization Expense (Details) Details 95 false false R96.htm 995639 - Disclosure - Note 9 - Loan Servicing (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-9-loan-servicing-details-textual Note 9 - Loan Servicing (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-9-loan-servicing-tables 96 false false R97.htm 995640 - Disclosure - Note 9 - Loan Servicing - Schedule of Servicing Assets at Fair Value (Details) Sheet http://www.alerus.com/20251231/role/statement-note-9-loan-servicing-schedule-of-servicing-assets-at-fair-value-details Note 9 - Loan Servicing - Schedule of Servicing Assets at Fair Value (Details) Details 97 false false R98.htm 995641 - Disclosure - Note 9 - Loan Servicing - Schedule of Servicing Assets at Amortized Value (Details) Sheet http://www.alerus.com/20251231/role/statement-note-9-loan-servicing-schedule-of-servicing-assets-at-amortized-value-details Note 9 - Loan Servicing - Schedule of Servicing Assets at Amortized Value (Details) Details 98 false false R99.htm 995642 - Disclosure - Note 9 - Loan Servicing - Summary of Activity Related to Loan Servicing (Details) Sheet http://www.alerus.com/20251231/role/statement-note-9-loan-servicing-summary-of-activity-related-to-loan-servicing-details Note 9 - Loan Servicing - Summary of Activity Related to Loan Servicing (Details) Details 99 false false R100.htm 995643 - Disclosure - Note 10 - Leases - Schedule of Lessee Assets and Liabilities (Details) Sheet http://www.alerus.com/20251231/role/statement-note-10-leases-schedule-of-lessee-assets-and-liabilities-details Note 10 - Leases - Schedule of Lessee Assets and Liabilities (Details) Details 100 false false R101.htm 995644 - Disclosure - Note 10 - Leases - Schedule of Lease Cost (Details) Sheet http://www.alerus.com/20251231/role/statement-note-10-leases-schedule-of-lease-cost-details Note 10 - Leases - Schedule of Lease Cost (Details) Details 101 false false R102.htm 995645 - Disclosure - Note 10 - Leases - Schedule of Lessee, Operating Lease, Liability, to be Paid, Maturity (Details) Sheet http://www.alerus.com/20251231/role/statement-note-10-leases-schedule-of-lessee-operating-lease-liability-to-be-paid-maturity-details Note 10 - Leases - Schedule of Lessee, Operating Lease, Liability, to be Paid, Maturity (Details) Details 102 false false R103.htm 995646 - Disclosure - Note 11 - Other Assets - Schedule of Other Assets (Details) Sheet http://www.alerus.com/20251231/role/statement-note-11-other-assets-schedule-of-other-assets-details Note 11 - Other Assets - Schedule of Other Assets (Details) Details 103 false false R104.htm 995647 - Disclosure - Note 11 - Other Assets - Schedule of Other Assets (Details) (Parentheticals) Sheet http://www.alerus.com/20251231/role/statement-note-11-other-assets-schedule-of-other-assets-details-parentheticals Note 11 - Other Assets - Schedule of Other Assets (Details) (Parentheticals) Details 104 false false R105.htm 995648 - Disclosure - Note 12 - Deposits (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-12-deposits-details-textual Note 12 - Deposits (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-12-deposits-tables 105 false false R106.htm 995649 - Disclosure - Note 12 - Deposits - Schedule of Deposit Liabilities, Type (Details) Sheet http://www.alerus.com/20251231/role/statement-note-12-deposits-schedule-of-deposit-liabilities-type-details Note 12 - Deposits - Schedule of Deposit Liabilities, Type (Details) Details 106 false false R107.htm 995650 - Disclosure - Note 12 - Deposits - Schedule of Certificate of Deposit Maturities (Details) Sheet http://www.alerus.com/20251231/role/statement-note-12-deposits-schedule-of-certificate-of-deposit-maturities-details Note 12 - Deposits - Schedule of Certificate of Deposit Maturities (Details) Details 107 false false R108.htm 995651 - Disclosure - Note 13 - Short-term Borrowings (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-13-shortterm-borrowings-details-textual Note 13 - Short-term Borrowings (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-13-shortterm-borrowings-tables 108 false false R109.htm 995652 - Disclosure - Note 13 - Short-Term Borrowings - Schedule of Short-term Debt (Details) Sheet http://www.alerus.com/20251231/role/statement-note-13-shortterm-borrowings-schedule-of-shortterm-debt-details Note 13 - Short-Term Borrowings - Schedule of Short-term Debt (Details) Details 109 false false R110.htm 995653 - Disclosure - Note 14 - Long-term Debt - Schedule of Long-term Debt (Details) Sheet http://www.alerus.com/20251231/role/statement-note-14-longterm-debt-schedule-of-longterm-debt-details Note 14 - Long-term Debt - Schedule of Long-term Debt (Details) Details 110 false false R111.htm 995654 - Disclosure - Note 14 - Long-term Debt - Schedule of Long-term Debt (Details) (Parentheticals) Sheet http://www.alerus.com/20251231/role/statement-note-14-longterm-debt-schedule-of-longterm-debt-details-parentheticals Note 14 - Long-term Debt - Schedule of Long-term Debt (Details) (Parentheticals) Details 111 false false R112.htm 995655 - Disclosure - Note 15 - Commitments and Contingencies (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-15-commitments-and-contingencies-details-textual Note 15 - Commitments and Contingencies (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-15-commitments-and-contingencies-tables 112 false false R113.htm 995656 - Disclosure - Note 15 - Commitments and Contingencies - Schedule of Fair Value, Off Balance Sheet Risks (Details) Sheet http://www.alerus.com/20251231/role/statement-note-15-commitments-and-contingencies-schedule-of-fair-value-off-balance-sheet-risks-details Note 15 - Commitments and Contingencies - Schedule of Fair Value, Off Balance Sheet Risks (Details) Details 113 false false R114.htm 995657 - Disclosure - Note 17 - Share-based Compensation Plan (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan-details-textual Note 17 - Share-based Compensation Plan (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan-tables 114 false false R115.htm 995658 - Disclosure - Note 17 - Share-based Compensation Plan - Schedule of Share-Based Compensation for Restricted Stock and Restricted Stock Units (Details) Sheet http://www.alerus.com/20251231/role/statement-note-17-sharebased-compensation-plan-schedule-of-sharebased-compensation-for-restricted-stock-and-restricted-stock-units-details Note 17 - Share-based Compensation Plan - Schedule of Share-Based Compensation for Restricted Stock and Restricted Stock Units (Details) Details 115 false false R116.htm 995659 - Disclosure - Note 18 - Employee Benefits (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-18-employee-benefits-details-textual Note 18 - Employee Benefits (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-18-employee-benefits-tables 116 false false R117.htm 995660 - Disclosure - Note 18 - Employee Benefits - Schedule of Costs of Retirement Plans (Details) Sheet http://www.alerus.com/20251231/role/statement-note-18-employee-benefits-schedule-of-costs-of-retirement-plans-details Note 18 - Employee Benefits - Schedule of Costs of Retirement Plans (Details) Details 117 false false R118.htm 995661 - Disclosure - Note 19 - Noninterest Income - Schedule of Disaggregation of Revenue (Details) Sheet http://www.alerus.com/20251231/role/statement-note-19-noninterest-income-schedule-of-disaggregation-of-revenue-details Note 19 - Noninterest Income - Schedule of Disaggregation of Revenue (Details) Details 118 false false R119.htm 995662 - Disclosure - Note 20 - Income Taxes (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-details-textual Note 20 - Income Taxes (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-20-income-taxes-tables 119 false false R120.htm 995663 - Disclosure - Note 20 - Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-schedule-of-components-of-income-tax-expense-benefit-details Note 20 - Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) Details 120 false false R121.htm 995664 - Disclosure - Note 20 - Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-schedule-of-deferred-tax-assets-and-liabilities-details Note 20 - Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) Details 121 false false R122.htm 995665 - Disclosure - Note 20 - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-schedule-of-effective-income-tax-rate-reconciliation-details Note 20 - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) Details 122 false false R123.htm 995666 - Disclosure - Note 20 - Income Taxes - Schedule of Income Taxes Paid (Details) Sheet http://www.alerus.com/20251231/role/statement-note-20-income-taxes-schedule-of-income-taxes-paid-details Note 20 - Income Taxes - Schedule of Income Taxes Paid (Details) Details 123 false false R124.htm 995667 - Disclosure - Note 21 - Tax Credit Investments - Schedule of Tax Credit Investments (Details) Sheet http://www.alerus.com/20251231/role/statement-note-21-tax-credit-investments-schedule-of-tax-credit-investments-details Note 21 - Tax Credit Investments - Schedule of Tax Credit Investments (Details) Details 124 false false R125.htm 995668 - Disclosure - Note 21 - Tax Credit Investments - Schedule of Amortization Expense and Tax Benefit (Details) Sheet http://www.alerus.com/20251231/role/statement-note-21-tax-credit-investments-schedule-of-amortization-expense-and-tax-benefit-details Note 21 - Tax Credit Investments - Schedule of Amortization Expense and Tax Benefit (Details) Details 125 false false R126.htm 995669 - Disclosure - Note 22 - Segment Reporting (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-22-segment-reporting-details-textual Note 22 - Segment Reporting (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-22-segment-reporting-tables 126 false false R127.htm 995670 - Disclosure - Note 22 - Segment Reporting - Schedule of Segment Reporting Information, by Segment (Details) Sheet http://www.alerus.com/20251231/role/statement-note-22-segment-reporting-schedule-of-segment-reporting-information-by-segment-details Note 22 - Segment Reporting - Schedule of Segment Reporting Information, by Segment (Details) Details 127 false false R128.htm 995671 - Disclosure - Note 23 - Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) Sheet http://www.alerus.com/20251231/role/statement-note-23-earnings-per-share-schedule-of-earnings-per-share-basic-and-diluted-details Note 23 - Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) Details 128 false false R129.htm 995672 - Disclosure - Note 24 - Related Party Transactions (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions-details-textual Note 24 - Related Party Transactions (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions-tables 129 false false R130.htm 995673 - Disclosure - Note 24 - Related Party Transactions - Schedule of Related Party Transactions (Details) Sheet http://www.alerus.com/20251231/role/statement-note-24-related-party-transactions-schedule-of-related-party-transactions-details Note 24 - Related Party Transactions - Schedule of Related Party Transactions (Details) Details 130 false false R131.htm 995674 - Disclosure - Note 25 - Derivative Instruments (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-details-textual Note 25 - Derivative Instruments (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-tables 131 false false R132.htm 995675 - Disclosure - Note 25 - Derivative Instruments - Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-schedule-of-derivative-instruments-in-statement-of-financial-position-fair-value-details Note 25 - Derivative Instruments - Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details) Details 132 false false R133.htm 995676 - Disclosure - Note 25 - Derivative Instruments - Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) (Details) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-schedule-of-cash-flow-hedges-included-in-accumulated-other-comprehensive-income-loss-details Note 25 - Derivative Instruments - Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) (Details) Details 133 false false R134.htm 995677 - Disclosure - Note 25 - Derivative Instruments - Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location (Details) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-schedule-of-cash-flow-hedging-instruments-statements-of-financial-performance-and-financial-position-location-details Note 25 - Derivative Instruments - Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location (Details) Details 134 false false R135.htm 995678 - Disclosure - Note 25 - Derivative Instruments - Schedule of Gain/(Losses) in Derivative Instruments (Details) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-schedule-of-gainlosses-in-derivative-instruments-details Note 25 - Derivative Instruments - Schedule of Gain/(Losses) in Derivative Instruments (Details) Details 135 false false R136.htm 995679 - Disclosure - Note 25 - Derivative Instruments - Schedule Of Offsetting Derivative Assets And Liabilities (Details) Sheet http://www.alerus.com/20251231/role/statement-note-25-derivative-instruments-schedule-of-offsetting-derivative-assets-and-liabilities-details Note 25 - Derivative Instruments - Schedule Of Offsetting Derivative Assets And Liabilities (Details) Details 136 false false R137.htm 995680 - Disclosure - Note 26 - Regulatory Matters - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) Sheet http://www.alerus.com/20251231/role/statement-note-26-regulatory-matters-schedule-of-compliance-with-regulatory-capital-requirements-under-banking-regulations-details Note 26 - Regulatory Matters - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) Details 137 false false R138.htm 995681 - Disclosure - Note 27 - Other Comprehensive Income (Loss) - Schedule of Comprehensive Income (Loss) (Details) Sheet http://www.alerus.com/20251231/role/statement-note-27-other-comprehensive-income-loss-schedule-of-comprehensive-income-loss-details Note 27 - Other Comprehensive Income (Loss) - Schedule of Comprehensive Income (Loss) (Details) Details http://www.alerus.com/20251231/role/statement-note-27-other-comprehensive-income-loss-tables 138 false false R139.htm 995682 - Disclosure - Note 27 - Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) Sheet http://www.alerus.com/20251231/role/statement-note-27-other-comprehensive-income-loss-schedule-of-accumulated-other-comprehensive-income-loss-details Note 27 - Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) Details http://www.alerus.com/20251231/role/statement-note-27-other-comprehensive-income-loss-tables 139 false false R140.htm 995683 - Disclosure - Note 28 - Stock Repurchase Program (Details Textual) Sheet http://www.alerus.com/20251231/role/statement-note-28-stock-repurchase-program-details-textual Note 28 - Stock Repurchase Program (Details Textual) Details http://www.alerus.com/20251231/role/statement-note-28-stock-repurchase-program- 140 false false R141.htm 995684 - Disclosure - Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) Sheet http://www.alerus.com/20251231/role/statement-note-29-fair-value-of-assets-and-liabilities-schedule-of-fair-value-assets-and-liabilities-measured-on-recurring-basis-details Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) Details 141 false false R142.htm 995685 - Disclosure - Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (Parentheticals) Sheet http://www.alerus.com/20251231/role/statement-note-29-fair-value-of-assets-and-liabilities-schedule-of-fair-value-assets-and-liabilities-measured-on-recurring-basis-details-parentheticals Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) (Parentheticals) Details 142 false false R143.htm 995686 - Disclosure - Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value Assets Measured on a Nonrecurring Basis (Details) Sheet http://www.alerus.com/20251231/role/statement-note-29-fair-value-of-assets-and-liabilities-schedule-of-fair-value-assets-measured-on-a-nonrecurring-basis-details Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Value Assets Measured on a Nonrecurring Basis (Details) Details 143 false false R144.htm 995687 - Disclosure - Note 29 - Fair Value of Assets and Liabilities - Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques (Details) Sheet http://www.alerus.com/20251231/role/statement-note-29-fair-value-of-assets-and-liabilities-fair-value-assets-and-liabilities-measured-on-nonrecurring-basis-valuation-techniques-details Note 29 - Fair Value of Assets and Liabilities - Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques (Details) Details 144 false false R145.htm 995688 - Disclosure - Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Values by Balance Sheet Groupings (Details) Sheet http://www.alerus.com/20251231/role/statement-note-29-fair-value-of-assets-and-liabilities-schedule-of-fair-values-by-balance-sheet-groupings-details Note 29 - Fair Value of Assets and Liabilities - Schedule of Fair Values by Balance Sheet Groupings (Details) Details 145 false false R146.htm 995689 - Disclosure - Note 30 - Parent Company Only Financial Statements - Parent Company Condensed Balance Sheets (Details) Sheet http://www.alerus.com/20251231/role/statement-note-30-parent-company-only-financial-statements-parent-company-condensed-balance-sheets-details Note 30 - Parent Company Only Financial Statements - Parent Company Condensed Balance Sheets (Details) Details 146 false false R147.htm 995690 - Disclosure - Note 30 - Parent Company Only Financial Statements - Parent Company Condensed Statements of Income (Details) Sheet http://www.alerus.com/20251231/role/statement-note-30-parent-company-only-financial-statements-parent-company-condensed-statements-of-income-details Note 30 - Parent Company Only Financial Statements - Parent Company Condensed Statements of Income (Details) Details 147 false false R148.htm 995691 - Disclosure - Note 30 - Parent Company Only Financial Statements - 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