Document And Entity Information Due after 10 years, Available-for-sale, Fair Value Note To Financial Statement Details Textual Derivative, Gain (Loss) on Derivative, Net us-gaap_DerivativeGainLossOnDerivativeNet Derivative, Gain (Loss) on Derivatives, Net Significant Accounting Policies us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis Available-for-sale, Amortized Cost Note 3 - Business Combinations Due within one year or less, Available-for-sale, Amortized Cost Note 5 - Investment Securities us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate Available-for-sale, Fair Value us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent Net change, after-tax amount Note 6 - Loans and Allowance for Credit Losses Due within one year or less, Available-for-sale, Fair Value Note 7 - Land, Premises and Equipment, Net Due after one year through five years, Available-for-sale, Fair Value Note 8 - Goodwill and Other Intangible Assets Due after five years through ten years, Available-for-sale, Fair Value Note 9 - Loan Servicing Residential Mortgage-Backed Securities [Member] Note 10 - Leases Note 11 - Other Assets Commercial Mortgage-Backed Securities [Member] Note 12 - Deposits Note 13 - Short-term Borrowings us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax Change in fair value, after-tax amount Note 14 - Long-term Debt Note 15 - Commitments and Contingencies Note 17 - Share-based Compensation Plan us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax Less: reclassification adjustment for net realized losses (2), after-tax amount Note 18 - Employee Benefits Note 19 - Noninterest Income Note 20 - Income Taxes Note 21 - Tax Credit Investments Asset-Backed Securities [Member] Note 22 - Segment Reporting Note 23 - Earnings Per Share Note 24 - Related Party Transactions Note 25 - Derivative Instruments Note 26 - Regulatory Matters US States and Political Subdivisions Debt Securities [Member] Note 27 - Other Comprehensive Income (Loss) Note 29 - 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Note 18 - Employee Benefits - Schedule of Costs of Retirement Plans (Details) Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Note 19 - Noninterest Income - Schedule of Disaggregation of Revenue (Details) Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Note 20 - Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) Note 20 - Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) Note 20 - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) Note 20 - Income Taxes - Schedule of Income Taxes Paid (Details) Note 21 - Tax Credit Investments - Schedule of Tax Credit Investments (Details) Note 21 - Tax Credit Investments - Schedule of Amortization Expense and Tax Benefit (Details) Note 22 - Segment Reporting - Schedule of Segment Reporting Information, by Segment (Details) Note 23 - Earnings Per Share - Schedule of Earnings Per 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(Year) Legal Matters and Contingencies [Text Block] Deferred income taxes, net Deferred income taxes, net Share-Based Payment Arrangement [Text Block] us-gaap_IncomeTaxReceivable Income tax refund receivable us-gaap_PrepaidExpenseCurrentAndNoncurrent Prepaid expenses Other Assets Other assets Total Award Type [Domain] Award Type [Axis] us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Net Finite-Lived Intangible Asset, Expected Amortization, Total Other intangible assets, net Standby Letters of Credit [Member] Finite-Lived Intangible Assets, Gross Loss Contingencies [Table] Commitments and Contingencies Disclosure [Text Block] us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less accumulated depreciation Land, premises and equipment, net Total Goodwill Goodwill Property, Plant and Equipment, Gross Schedule of Assumptions for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Table Text Block] Derivative Liability, Subject to Master Netting Arrangement, before Offset us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue (Increase) decrease in company-owned life insurance (Increase) in value of bank-owned life insurance Derivative Asset, Subject to Master Netting Arrangement, before Offset Derivative Asset, Fair Value Derivative instruments Derivative Instrument [Axis] Derivative Contract [Domain] Federal Home Loan Bank Advances [Member] Trading Debt Securities, Trading Fair value of servicing rights Fair value, beginning of period Fair value, end of period Federal Funds Purchased [Member] Less valuation reserve us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures Investment in subsidiaries us-gaap_IncomeLossFromEquityMethodInvestments Equity in undistributed income of subsidiaries Equity in undistributed income of subsidiaries Income (Loss) from Continuing 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Amendment Flag City Area Code Use of Estimates, Policy [Policy Text Block] Reclassification, Comparability Adjustment [Policy Text Block] us-gaap_GainLossOnSaleOfPropertyPlantEquipment Realized loss (gain) on sale of premises and equipment Gain (loss) on sale of premises and equipment us-gaap_GainsLossesOnSalesOfOtherRealEstate Realized loss (gain) on sale of foreclosed assets Current Fiscal Year End Date Gain on sale of non-mortgage loans Realized loss (gain) on non-mortgage loans sold Gain on sale of non-mortgage loans us-gaap_GainLossOnSaleOfMortgageLoans Realized loss (gain) on mortgage loans sold Interest Receivable Interest Receivable Document Fiscal Period Focus Document Fiscal Year Focus Consolidation, Policy [Policy Text Block] Document Period End Date Entity File Number Banking Regulation, Tier 1 Leverage Capital Ratio, Actual Banking Regulation, Tier 1 Leverage Capital Ratio, Capital Adequacy, Minimum Entity Emerging Growth Company Residential agency, Held-to-maturity, Fair Value Banking Regulation, Tier 1 Leverage Capital Ratio, Well Capitalized, Minimum Document Type Banking Regulation, Total Risk-Based Capital Ratio, Well Capitalized, Minimum Entity Small Business Entity Shell Company Banking Regulation, Common Equity Tier 1 Risk-Based Capital Ratio, Actual Document Information [Line Items] Document Information [Table] us-gaap_CashAndSecuritiesSegregatedUnderFederalAndOtherRegulations Cash and Securities Segregated under Federal and Other Regulations Banking Regulation, Total Risk-Based Capital Ratio, Actual Banking Regulation, Total Risk-Based Capital Ratio, Capital Adequacy, Minimum Entity Public Float Entity Filer Category us-gaap_InvestmentOwnedBalanceShares Investment Owned, Balance, Shares (in shares) Banking Regulation, Tier 1 Risk-Based Capital Ratio, Actual Entity Current Reporting Status Banking Regulation, Tier 1 Risk-Based Capital Ratio, Capital Adequacy, Minimum Entity Voluntary Filers us-gaap_BusinessCombinationAcquisitionRelatedCosts 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Intangible amortization expense Amortization of Intangible Assets ecd_NonRule10b51ArrTrmntdFlag Non-Rule 10b5-1 Arrangement Terminated [Flag] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Entity Address, City or Town ecd_Rule10b51ArrTrmntdFlag Rule 10b5-1 Arrangement Terminated [Flag] ecd_Rule10b51ArrAdoptedFlag Rule 10b5-1 Arrangement Adopted [Flag] alrs_IncreaseDecreaseinMortgageServicingRightsFairValue Change in fair value of mortgage servicing rights Represents information pertaining to the increase/decrease in the fair value of mortgage servicing rights. Regulatory Capital Requirements under Banking Regulations [Text Block] Entity Address, Postal Zip Code Entity Address, State or Province Concentration Risk Type [Axis] ecd_NonRule10b51ArrAdoptedFlag Non-Rule 10b5-1 Arrangement Adopted [Flag] Servicing rights capitalized upon sale of mortgage loans The amount capitalized from the sale of mortgage servicing rights. Concentration Risk Type [Domain] Material Terms of Trading Arrangement [Text Block] us-gaap_ForeclosedAssets Foreclosed assets Entity Common Stock, Shares Outstanding Trading Arrangements, by Individual [Table] Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Marketable Securities [Table Text Block] Metro Phoenix Bank and HMN Financial Inc. [Member] Represents information pertaining to Metro Phoenix Bank and HMN Financial Inc. Supplies and postage Professional fees and assessments alrs_NumberOfBankingOffices Number Of Banking Offices The number of banking office. Trading Symbol Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Investment Holdings [Table] Premises and equipment transferred to other assets The amount of property plant and equipment transferred to other assets. Local Phone Number us-gaap_TableTextBlock Notes Tables Financing Receivable, Excluding Accrued Interest, Modified, Weighted Average Interest Rate Decrease from Modification Percentage of decrease in weighted average contractual interest rate of financing receivable modified (excluding accrued interest) for debtor experiencing financial difficulty. Mortgage-backed securities, Carrying Amount Financing Receivable, Excluding Accrued Interest, Modified, Weighted Average Interest Rate Decrease from Modification (Year) Period of increase in weighted average maturity of financing receivable modified (excluding accrued interest) for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days us-gaap_GainLossOnSaleOfInvestments Net gains (losses) on investment securities (1) FHLB Federal Home Loan Bank stock Federal Reserve Federal Reserve Bank stock us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds Debt Securities, Held-to-maturity, Fair Value Total investment securities, Held-to-maturity, Fair Value alrs_ClientSwapFees Client swap fees Represents information pertaining to client swap fees. us-gaap_TaxBasisOfInvestmentsCostForIncomeTaxPurposes Investment, Tax Basis, Cost alrs_ServicingAssetAtFairValueAcquisitions Servicing assets acquired in business combination The value of new servicing assets acquired in current period from business combination. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansHeldForSale Loans held for sale Amount of assets related to loans held for sale acquired at the acquisition date. Schedule of Financing Receivables, Purchased with Credit Deterioration [Table Text Block] The entire tabular disclosure of financing receivables that were purchased with credit deterioration. Derivative Instruments, Gain (Loss) [Table Text Block] us-gaap_InterestExpense Expenses alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedServicingRights Servicing rights The amount of servicing assets acquired as of the acquisition date. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingRightofuseAsset Operating lease right-of-use assets The amount of operating lease right-of-use assets acquired at the date of an acquisition. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilities Operating lease liabilities The amount of operating lease liabilities acquired as of the date of acquisition. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredIncomeTaxesNet Deferred income taxes, net The amount of deferred income taxes, net acquired as of the date of acquisition. us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Derivative Instruments and Hedging Activities Disclosure [Text Block] us-gaap_InterestExpenseLongTermDebt Long-term debt Subsequent Event [Table] Defined Benefit Plan [Table] Total amounts in the Consolidated Statements of Income, Short-term Borrowings Short-term borrowings Subsequent Events [Text Block] alrs_BusinessAcquisitionGoodwillAmountNotExpectedToBeTaxDeductible Business Acquisition, Goodwill, Amount Not Expected to Be Tax Deductible The amount of goodwill arising from a business combination that is not expected to be deductible for tax purposes. 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Section 291 Interest Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible interest expense. Accounting Standards Update 2016-13 [Member] us-gaap_CurrentFederalTaxExpenseBenefit Current federal income tax expense alrs_DiscontinuedFairValueHedgeTerminationFeePaid Discontinued Fair Value Hedge, Termination Fee Paid Amount of termination fee paid on discontinued fair value hedge. us-gaap_DeferredFederalIncomeTaxExpenseBenefit Deferred federal income tax Derivative Liability, Subject to Master Netting Arrangement, after Offset Collateral Held [Domain] Collateral Pledged [Member] Derivative Liability, Statement of Financial Position [Extensible Enumeration] Real Estate [Member] Section 291 Interest, percent Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for interest expense. Unfunded Loan Commitment [Member] Loans Unsecured by Real Estate [Member] Represents information pertaining to the loans that are not secured through real estate. Commercial and Industrial Portfolio Segments [Member] Represents information pertaining to commercial and industrial portfolio segments. Collateral Held [Axis] alrs_EffectiveIncomeTaxRateReconciliationReductionInDeficitPercentage Reduction in Deficit, percent Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to reduction in deficit. us-gaap_CurrentIncomeTaxExpenseBenefit Current income tax Life Insurance, Corporate or Bank Owned, Policy [Policy Text Block] Disclosure of accounting policy for bank owned life insurance. Class of Financing Receivable [Domain] Accrued Interest Receivable [Policy Text Block] Disclosure of accounting policy for accrued interest receivable, including receivables related to investments and loans. Construction Loans [Member] Tax Credit Investments [Policy Text Block] Disclosure of accounting policy for tax credit investments. Home Equity Loan [Member] Minnesota Department of Revenue [Member] Represents Minnesota Department of Revenue. Schedule of Income Taxes Paid [Table Text Block] Tabular disclosure of the components of income taxes paid. Allowance For Credit Losses on Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block] Description of accounting policies and methodologies used to estimate the entity's liability from the allowance for credit losses on off-balance sheet credit exposures and related charges for those credit exposures. Other States Tax Authorities [Member] Represents Other States Tax Authorities. Commercial Real Estate Portfolio Segment [Member] Class of Financing Receivable [Axis] North Dakota Office of State Tax Commissioner [Member] Represents North Dakota Office of State Tax Commissioner. Financing Receivable Portfolio Segment [Domain] us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest Income before income taxes Income before income taxes Commercial Portfolio Segment [Member] Residential Portfolio Segment [Member] alrs_ReclassificationAdjustmentForNetRealizedLossesCurrentPeriodNetOfTax Less: reclassification adjustment for net realized losses Amount after tax of reclassification adjustments for net realized losses. Consumer Portfolio Segment [Member] alrs_PercentageOfCompanyLoansLiborUsedAsIndexRate Percentage of Company Loans, LIBOR Used as Index Rate The percentage of company loans on which LIBOR is used as index rate. Financing Receivable Portfolio Segment [Axis] us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss ICFR Auditor Attestation Flag Comprehensive Income (Loss) Note [Text Block] us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Other Comprehensive Income (Loss), Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Mortgage Banking Activity [Policy Text Block] us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPeriodIncreaseDecrease Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Period Increase (Decrease) State and Local Jurisdiction [Member] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Domain] us-gaap_FinancingReceivableExcludingAccruedInterest90DaysOrMorePastDueStillAccruing Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing Internal Revenue Service (IRS) [Member] Income Tax Jurisdiction [Axis] Income Tax Jurisdiction [Domain] Disaggregation of Revenue [Table Text Block] Disaggregation of Revenue [Table] Financing Receivable, Held-for-Investment, Foreclosed Asset [Policy Text Block] us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Domestic Tax Jurisdiction [Member] us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestAfterAllowanceForCreditLoss Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss Financing Receivable [Policy Text Block] Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Recovery us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Recovery Financing Receivable, Held-for-Sale [Policy Text Block] alrs_DeferredTaxAssetOperatingLeaseLiability Operating lease liabilities Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from operating lease liabilities. Loans, Gross Charge-offs Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Charge-offs Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Charge-offs Revenue from Contract with Customer [Text Block] us-gaap_FinancingReceivableExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate Financing Receivable, Excluding Accrued Interest, Purchased with Credit Deterioration, Allowance for Credit Loss at Acquisition Date alrs_MortgageBankingIncome Mortgage banking (1) The amount of noninterest income from mortgage banking. Cash and Cash Equivalents, Policy [Policy Text Block] Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Provisions us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Provisions us-gaap_FinancingReceivableExcludingAccruedInterestNonaccrual Financing Receivable, Excluding Accrued Interest, Nonaccrual us-gaap_FinancingReceivableExcludingAccruedInterestNonaccrualNoAllowance Financing Receivable, Excluding Accrued Interest, Nonaccrual, No Allowance us-gaap_FinancingReceivableExcludingAccruedInterestTransferToHeldForSaleAllowanceForCreditLossExpenseReversal Financing Receivable, Excluding Accrued Interest, Transfer out, Allowance for Credit Loss, Expense Reversal alrs_NumberOfEmployeeRetirementPlans Number of Employee Retirement Plans The number of employee retirement plans offered by the company. Accounting Policies [Abstract] Significant Accounting Policies [Text Block] Defined Contribution Salary Reduction Plan [Member] Represents information pertaining to the defined contribution salary reduction plan. Interchange Fees [Member] Represents information pertaining to interchange fees. Other Noninterest [Member] Represents information pertaining to other noninterest related products and services. Transactional Fees [Member] Represents information pertaining to transactional fees. Dividends declared per common share (in dollars per share) alrs_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchThresholdThreeToSixPercent Defined Contribution Plan, Employer Matching Contribution, Percent of Match Threshold, Three to Six Percent Percentage employer matches of the employee's percentage contribution matched between 3% and 6%. Loans Receivable [Member] alrs_LettersOfCreditNumberOutstanding Letters of Credit, Number Outstanding The number of outstanding letters of credit. Mortgage Receivable [Member] Receivable Type [Axis] Receivable [Domain] Condensed Financial Information of Parent Company Only Disclosure [Text Block] alrs_TrustFeesReceivable Trust fees accrued/receivable The amount of trust fees receivable. Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Auditor Name us-gaap_ContinuingInvolvementWithTransferredFinancialAssetsPrincipalAmountOutstanding Continuing Involvement with Transferred Financial Assets, Principal Amount Outstanding Net increase (decrease) in short-term borrowings with maturities of three months or less Income Tax Contingency [Table] Accrued Liabilities and Other Liabilities Accrued expenses and other liabilities Auditor Firm ID Auditor Location Net loans Net loans The amount of loans recognized as of the acquisition date. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits Deposits The amount of deposits recognized as of the acquisition date. Dilutive effect of stock-based awards (in shares) Pledging Purpose [Domain] Investment Tax Credit Carryforward [Member] Diluted average common shares outstanding (in shares) Weighted-average common shares outstanding for diluted earnings per share (in shares) Tax Credit Carryforward [Table] Tax Credit Carryforward [Axis] Pledging Purpose [Axis] Tax Credit Carryforward, Name [Domain] alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets Other assets Amount of other assets acquired at the acquisition date. alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities Accrued expenses and other liabilities Amount of other liabilities assumed at the acquisition date. us-gaap_CashReserveDepositRequiredAndMade Cash Reserve Deposit Required and Made alrs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestReceivable Accrued interest receivable The amount of accrued interest receivable recognized as of the acquisition date. Statement of Financial Position [Abstract] Diluted earnings per common share (in dollars per share) Average common shares outstanding (in shares) alrs_BusinessAcquisitionProFormaNoninterestExpense Noninterest expense The pro forma non-interest income for a period as if the business combination or combinations had been completed at the beginning of the period. alrs_BusinessAcquisitionProFormaNoninterestIncome Noninterest income The pro forma non-interest income for a period as if the business combination or combinations had been completed at the beginning of the period. 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Statement of Cash Flows [Abstract] us-gaap_FinancingReceivableUnamortizedPurchasePremiumDiscount Financing Receivable, Unamortized Purchase Premium (Discount) us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome Tax Exempt Interest, percent Statement of Stockholders' Equity [Abstract] Financing Receivable, Nonaccrual [Table Text Block] Mortgage and lending expenses The amount of mortgage and lending expenses incurred during the period. Interest on lease liabilities us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in shares) Business services, software and technology expense Business services, software and technology expense The amount of business services, software and technology expenses incurred during the period. Servicing rights Balance at beginning of period Balance at end of period, net of valuation reserve Amortized amount of contract, net of valuation allowance, for servicing assets. alrs_GainLossOnServicingRights Realized loss (gain) on servicing rights The amount of gain (loss) on servicing rights. Proceeds from calls of investment securities held-to-maturity The cash inflow associated with the sale or calls of securities that had been designated as held-to-maturity. Amortization of right-of-use assets Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of Deferred Tax Assets and Liabilities [Table Text Block] alrs_RealizedLossGainOnBankOwnedLifeInsuranceMortality Realized loss (gain) on BOLI mortality The amount of gain (loss) on bank owned life insurance mortality. Other, percent us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Net increase (decrease) in deposits Schedule of Realized Gain (Loss) [Table Text Block] Share Repurchase Program [Table] HMN Financial Inc. (HNMF) [Member] Represents information pertaining to HMN Financial Incorporated. us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsInvestment Proportional Amortization of LIHTC Credits, percent Share Repurchase Program [Domain] Share Repurchase Program [Axis] Change in fair value hedges presented within residential real estate loans and other assets Value of change in fair value hedge within real estate loans and other assets (liabilities). us-gaap_DebtSecuritiesHeldToMaturityNonaccrualInterestIncome Debt Securities, Held-to-Maturity, Nonaccrual, Interest Income Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block] us-gaap_LoansAndLeasesReceivableRelatedParties Beginning balance Ending balance State and local income taxes, net of federal benefits(1), percent Fair Value Measurements, Nonrecurring [Table Text Block] Contractual Interest Rate Reduction [Member] Other srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased Share Repurchase Program, Authorized, Number of Shares (in shares) Financing activities U.S. federal statutory income tax, percent Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Corporate Bond Securities [Member] us-gaap_IncomeTaxReconciliationTaxExemptIncome Tax Exempt Interest us-gaap_PaymentsToAcquireLifeInsurancePolicies Purchases of company-owned life insurance Purchases of BOLI Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Proceeds from BOLI mortality claim us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates Net cash received (paid) for business combinations Preferred Class A [Member] us-gaap_OciDebtSecuritiesAvailableForSaleTransferToHeldToMaturityAdjustmentFromAociForAmortizationOfGainLossTax Less: reclassification adjustment from amortization of securities transferred from AFS to HTM (1), tax expense (benefit) Preferred Class B [Member] us-gaap_OciDebtSecuritiesAvailableForSaleTransferToHeldToMaturityAdjustmentFromAociForAmortizationOfGainLossBeforeTax Less: reclassification adjustment from amortization of securities transferred from AFS to HTM (1), pre-tax amount us-gaap_OciDebtSecuritiesAvailableForSaleTransferToHeldToMaturityAdjustmentFromAociForAmortizationOfGainLossAfterTax Less: reclassification adjustment from amortization of securities transferred from AFS to HTM (1), after-tax amount us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet Excess assets over liabilities Pledged Status [Domain] Pledged Status [Axis] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities Total liabilities us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired Net cash (paid) for business combinations Allowance for Credit Losses, Available-for-sale Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest Other us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther Class of Stock [Axis] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Cash paid for HMNF Comprehensive Income (Loss) [Table Text Block] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt Short-term borrowings Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Total investment securities, Available-for-sale, Amortized Cost us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Total assets us-gaap_DeferredTaxAssetInterestCarryforward Nonaccrual loan interest Restricted Stock and Restricted Stock Units [Member] Represents information pertaining to restricted stock and restricted stock units. us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAmortizedCostBeforeAllowanceForCreditLoss Debt Securities, Available-for-Sale and Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss Amortized Cost, Total investment securities 2019 Equity Incentive Plan [Member] Represents information pertaining to the "2019 Equity Incentive Plan". us-gaap_IncomeTaxReconciliationTaxCreditsInvestment Proportional Amortization of LIHTC Credits Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block] us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain Unrealized Gains, Total investment securities us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss Unrealized Losses, Total investment securities State and local income taxes, net of federal benefits(1) us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment Land premises and equipment, net us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAllowanceForCreditLoss Allowance for Credit Losses, Total investment securities Bank of North Dakota [Member] Represents information pertaining to the Bank of North Dakota. Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles Core deposit intangible us-gaap_DerivativeNotionalAmount Mortgage-backed securities, Notional Amount Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest U.S. federal statutory income tax Old Stock Repurchase Program [Member] Represents information pertaining to the "Old Stock Repurchase Program". us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue Fair Value, Total investment securities Hedging Relationship [Domain] Fair Value Hedging [Member] Available-for-sale, at fair value (amortized cost of $516,737 and $686,556, respectively) Debt Securities, Available-for-Sale, Excluding Accrued Interest Total investment securities, Available-for-sale, Fair Value Cash Flow Hedging [Member] New Stock Repurchase Program [Member] Represents information pertaining to the "New Stock Repurchase Program". us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities Investment securities available-for-sale Not Designated as Hedging Instrument, Trading [Member] Income Tax Disclosure [Text Block] Held-to-maturity, at amortized cost (fair value of $228,009 and $236,986, respectively, with an allowance for credit losses on investments of $123 and $131, respectively) Hedging Relationship [Axis] Hedging Designation [Axis] us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents Cash and cash equivalents alrs_PercentageOfIncreaseInFinancingReceivableAllowanceForCreditLossExcludingAccruedInterest Percentage of Increase in Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest The percentage of increase in amount, excluding accrued interest, of allowance for credit loss on financing receivable. Hedging Designation [Domain] Designated as Hedging Instrument [Member] Metro Phoenix Bank [Member] Represents information pertaining to Metro Phoenix Bank. Amortized Cost, Held-to-maturity Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss Total investment securities Stock issued for HMNF Accumulated Other Comprehensive Income (Loss) [Table] Schedule of Other Assets [Table Text Block] us-gaap_BusinessCombinationConsiderationTransferred1 Business Combination, Consideration Transferred Proceeds from sale of non-mortgage loans held for sale Pass [Member] us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired Business Acquisition, Percentage of Voting Interests Acquired Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Proceeds from sales of trading investment securities Proceeds from sales of trading investment securities us-gaap_ProceedsFromSaleOfHeldToMaturitySecurities Proceeds from Sale of Held-to-Maturity Securities Proceeds from maturities and paydowns of investment securities held-to-maturity us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt Proceeds, AFS Securities Internal Credit Assessment [Axis] Proceeds from maturities of investment securities available-for-sale Internal Credit Assessment [Domain] Retirement and Benefit Services Segment [Member] Represents information pertaining to the retirement and benefit services segment. Banking Segment [Member] Represents information pertaining to the banking segment. Business Combination, Pro Forma Information [Table] us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss Net income (after tax) Business Combination, Pro Forma Information [Table Text Block] Consumer, Other [Member] Schedule of Costs of Retirement Plans [Table Text Block] Financing Receivables, Total [Member] Total financing receivables, when it serves as a benchmark in a concentration of risk calculation, representing the sum of all reported financing receivables as of the balance sheet date. Wealth Management Segment [Member] Represents information pertaining to the wealth management segment. us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt Purchases of investment securities available-for-sale us-gaap_PaymentsToAcquireTradingSecuritiesHeldforinvestment Purchases of trading investment securities Financial Asset, Past Due [Member] Retirement Plan Name [Axis] us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Allowance for credit losses on loans Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest, Beginning Balance Financing Receivable, Allowance for Credit Loss, Ending Balance Retirement Plan Name [Domain] Fair Value Adjustments [Member] Represents information pertaining to fair value adjustments. Reported Value by Acquiree [Member] Represents information pertaining to the reported value by the acquiree. Financial Asset, Not Past Due [Member] Goodwill and Intangible Assets Disclosure [Text Block] Schedule of Goodwill [Table Text Block] Derivative Asset, Notional Amount Goodwill [Table] Derivative Liability, Notional Amount Construction, Land, and Development [Member] Represents information pertaining to the construction, land, and development loans. Non-Owner Occupied [Member] Represents the information pertaining to non-owner occupied loans. us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss Net loans Multifamily Loan [Member] Represents information pertaining to multifamily loans. Long-Term Debt, Adjustment, Variable Rate Percentage points adjusted to the reference rate to compute the variable rate on a debt instrument. Loans Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss Real Estate, Junior Lien [Member] Represents information pertaining to junior liens on real estate loans. Visa [Member] Represents information pertaining to visa. Credit Facility [Axis] alrs_InvestmentOwnedConversionRatio Investment Owned, Conversion Ratio Conversion ratio for investments owned. Credit Facility [Domain] Business Combination, Recognized Asset Acquired and Liability Assumed [Table Text Block] Agricultural Real Estate Portfolio Segment [Member] Represents information pertaining to the portfolio segment of the company's total financing receivables related to agricultural real estate. us-gaap_FinancingReceivableNonaccrualInterestIncome Financing Receivable, Nonaccrual, Interest Income Owner Occupied Loans [Member] Represents the information pertaining to owner occupied loans. Real Estate, First Lien [Member] Represents information pertaining to first liens on real estate loans. Production Loans [Member] Represents information pertaining to production loans. Four Years before Current Fiscal Year Special Mention [Member] Three Years before Current Fiscal Year Substandard [Member] Current Fiscal Year Doubtful [Member] FHLB Borrowings, Deposits, and Other [Member] Represents information pertaining to FHLB borrowings, deposits, and other borrowings. Two Years before Current Fiscal Year More than Four Years before Current Fiscal Year us-gaap_StockIssued1 Issuance of common stock for the acquisition Revolving us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice Fair value of PCD loans at acquisition us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue Par value of PCD loans at acquisition us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate Allowance for credit losses at acquisition Loans transferred to non-mortgage loans held for sale Collateral, Other [Member] Represents information pertaining collateral categorized as other. 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Restricted Stock [Member] Schedule Of Offsetting Derivative Assets And Liabilities [Table Text Block] Tabular disclosure of derivative assets and derivative liabilities that are subject to offsetting, including master netting arrangements. Antidilutive Security, Excluded EPS Calculation [Table] Financial Asset, 30 to 59 Days Past Due [Member] Interest Rate Swap, By Customer [Member] Represents information pertaining to interest rate swaps by customer. Financial Asset, 60 to 89 Days Past Due [Member] Activity in Affordable Housing Program Obligation [Table Text Block] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Financing Receivable, Past Due [Table Text Block] Financial Asset, Aging [Axis] Interest Rate Swap, By Dealer Bank [Member] Represents information pertaining to interest rate swaps by dealer bank. 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Wealth Management [Member] Represents information pertaining to wealth management. Retirement and Benefit Services [Member] Represents information pertaining to retirement and benefit services. Income Tax Paid, State and Local Junior Subordinated Debenture Trust I [Member] Represents information pertaining to junior subordinated debenture trust one. Junior Subordinated Debenture Trust II [Member] Represents information pertaining to the junior subordinated debenture trust 2. 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Carrying Value Document Transition Report Document Financial Statement Error Correction [Flag] Short-term borrowings Balance as of end of period Entity Interactive Data Current Non-mortgage Loans [Member] Represents non-mortgage loans. 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