Document And Entity Information
Dividend yield
Due after ten years, AFS, fair value
us-gaap_DerivativeGainLossOnDerivativeNet
Derivative, Gain (Loss) on Derivative, Net
Note To Financial Statement Details Textual
Significant Accounting Policies
Note 2 - Investment Securities
Due within one year, AFS, amortized cost
Note 3 - Loans and Allowance for Credit Losses
Risk-free interest rate
Note 4 - Other Real Estate Owned
Due within one year, AFS, fair value
Note 5 - Bank Premises and Equipment
Due after one year through five years, AFS, fair value
Note 6 - Leases
Due after five years through ten years, AFS, fair value
Note 7 - Goodwill and Other Intangible Assets
Note 8 - Deposits
Residential Mortgage-Backed Securities [Member]
Note 11 - Other Borrowed Funds
Commercial Mortgage-Backed Securities [Member]
Note 12 - Derivative Financial Instruments
Note 13 - Stockholders' Equity
Unrealized gain (loss), available for sale, net of tax expense (benefit) of $3,423, ($1,026), and $951, respectively
Note 14 - Stock-Based Compensation
Note 16 - Income Taxes
Expected volatility
Note 17 - Fair Values of Financial Instruments
us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax
Reclassification of realized (gain) loss, available for sale, net of tax (expense) benefit of ($3), $158, and $67, respectively
Note 18 - Regulatory Matters
Note 19 - Commitments and Contingencies
Investment securities:
Note 21 - Parent Company Only Financial Statements
Commercial Real Estate [Member]
Note 22 - Earnings Per Common Share
Expected term (in years) (Year)
istr_ProceedsFromIssuanceOfPrivatePlacementNet
Proceeds from Issuance of Private Placement, Net
The net proceeds from the issuance of private placement.
Note 2 - Investment Securities - Amortized Cost and Fair Value of Investment Securities Classified as AFS (Details)
Note 2 - Investment Securities - Sales of Investments Classified as AFS (Details)
Note 2 - Investment Securities - Amortized Cost and Fair Value of Investment Securities Classified as HTM (Details)
Note 2 - Investment Securities - Summary of Continuous Unrealized Loss Position for Securities Classified as AFS (Details)
US States and Political Subdivisions Debt Securities [Member]
Note 2 - Investment Securities - Summary of Continuous Unrealized Loss Position for Securities Classified as HTM (Details)
Note 2 - Investment Securities - Contractual Maturity (Details)
Note 3 - Loans and Allowance for Credit Losses - Summary of Loans by Categories (Details)
Note 3 - Loans and Allowance for Credit Losses - Aging Analysis of Loans (Details)
Note 3 - Loans and Allowance for Credit Losses - Schedule of Nonaccrual Loans (Details)
Note 3 - Loans and Allowance for Credit Losses - Loan Portfolio by Category and Credit Quality Indicator (Details)
Note 3 - Loans and Allowance for Credit Losses - Loans to Related Parties (Details)
Note 3 - Loans and Allowance for Credit Losses - Allowance for Loan Losses (Details)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
12 Months or More, Unrealized Losses
Note 4 - Other Real Estate Owned - Real Estate Owned (Details)
Granted, weighted average grant date fair value (in dollars per share)
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Unrealized Losses
Note 5 - Bank Premises and Equipment - Bank Premises and Equipment (Details)
Earned and issued, weighted average grant date fair value (in dollars per share)
Note 6 - Leases - Quantitative Information Regarding Operating Leases (Details)
Forfeited, weighted average grant date fair value (in dollars per share)
Note 6 - Leases - Future Minimum Lease Payment (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
Balance, beginning of period, weighted average grant date fair value (in dollars per share)
Balance, end of period, weighted average grant date fair value (in dollars per share)
Note 7 - Goodwill and Other Intangible Assets - Core Deposit Intangible Assets (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Forfeited, shares (in shares)
Note 7 - Goodwill and Other Intangible Assets - Amortization Schedule for Core Deposit Intangible Assets (Details)
Note 8 - Deposits - Deposits (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Balance, shares (in shares)
Balance, shares (in shares)
Note 8 - Deposits - Scheduled Maturates of Time Deposits (Details)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Less than 12 Months, Unrealized Losses
Schedule of Derivative Instruments [Table Text Block]
US Government Corporations and Agencies Securities [Member]
Change in unrealized gain, net
Note 11 - Other Borrowed Funds - Federal Home Loan Bank Advances (Details)
Derivative [Table]
Note 11 - Other Borrowing Funds - Junior Subordinated Debt (Details)
Reclassification of realized loss, net
Granted, shares (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)
Note 12 - Derivative Financial Instruments - Schedule of Derivatives Instruments (Details)
Corporate Debt Securities [Member]
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Earned and issued, shares (in shares)
Note 12 - Derivative Financial Instruments - Offsetting of Derivative Instruments (Details)
Note 13 - Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details)
Note 14 - Stock-Based Compensation - Schedule of Stock Option Activity (Details)
Note 14 - Stock-Based Compensation - Schedule of Stock Option Valuation Assumptions (Details)
Note 14 - Stock-Based Compensation - Schedule of Restricted Stock Activity (Details)
Note 16 - Income Taxes - Income Tax Expense (Details)
Note 16 - Income Taxes - Summary of Provision for Federal Income Taxes (Details)
Note 16 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details)
Note 17 - Fair Values of Financial Instruments - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)
Exercisable, weighted average price (in dollars per share)
Note 17 - Fair Values of Financial Instruments - Reconciliation for Assets Measured at Fair Value on Recurring Basis Using significant Unobservable Inputs (Details)
Note 17 - Fair Values of Financial Instruments - Reconciliation for Assets Measured at Fair Value on Recurring Basis Using significant Unobservable Inputs (Details) (Parentheticals)
Exercisable, weighted average remaining contractual term (Year)
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value
Note 17 - Fair Values of Financial Instruments - Quantitative Information About Significant Unobservable Inputs Used in Fair Value Measurement (Details)
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions
Note 17 - Fair Values of Financial Instruments - Estimated Fair Value of Financial Instruments (Details)
Fair Value
us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Note 18 - Regulatory Matters - Summary of Actual Capital Amounts and Ratios (Details)
Note 19 - Commitments and Contingencies - Commitments to Extend Credit (Details)
Note 19 - Commitments and Contingencies - Summary of ACL on Unfunded Loan Commitments (Details)
Exercisable, shares (in shares)
Note 21 - Parent Company Only Financial Statements - Balance Sheets (Details)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block]
Note 21 - Parent Company Only Financial Statements - Statements of Operations (Details)
Outstanding, weighted average remaining contractual term (Year)
Note 21 - Parent Company Only Financial Statements - Statements of Cash Flows (Details)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value
Less than 12 Months, Fair Value
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Note 22 - Earnings Per Common Share - Earnings Per Share (Details)
Weighted average grant date fair value (in dollars per share)
12 Months or More, Fair Value
us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Note 22 - Earnings Per Common Share - Antidilutive Securities (Details)
Notes To Financial Statements
Notes To Financial Statements [Abstract]
Financial Instruments [Domain]
us-gaap_LoansAndLeasesReceivableRelatedPartiesProceeds
Repayments/changes in relationship
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Outstanding, weighted average price (in dollars per share)
Outstanding, weighted average price (in dollars per share)
Deposits [Member]
Forfeited, weighted average price (in dollars per share)
Financial Instrument [Axis]
New loans/changes in relationship
Granted, weighted average price (in dollars per share)
Exercised, weighted average price (in dollars per share)
Lessee, Operating Leases [Text Block]
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Outstanding, shares (in shares)
Outstanding, shares (in shares)
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]
us-gaap_PolicyTextBlockAbstract
Accounting Policies
Gross gains
us-gaap_DebtSecuritiesAvailableForSaleRealizedGain
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)
us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss
Gross losses
Debt Securities, Available-for-Sale [Table]
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Requisite Service Period (Year)
us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage
istr_DebtSecuritiesAvailableforsaleUnrealizedLossPositionPercentOfSecuritiesCostBasis
Debt Securities, Available-for-Sale, Unrealized Loss Position, Percent of Securities Cost Basis
The percent of securities cost basis for the unrealized loss position of debt securities available for sale.
Liabilities [Abstract]
istr_DebtSecuritiesAvailableforsaleUnrealizedLossPositionPercentOfAmortizedCostOfInvestmentSecuritiesPortfolio
Debt Securities, Available-for-Sale, Unrealized Loss Position, Percent of Amortized Cost of Investment Securities Portfolio
The percent of amortized cost of investment securities portfolio for unrealized loss position of debt securities available for sale.
Vesting [Axis]
Vesting [Domain]
Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Payment Arrangement, Tranche Two [Member]
us-gaap_Assets
Assets
Total assets
Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]
Plan Name [Axis]
Plan Name [Domain]
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount
Offsetting Interest Rate Swap [Member]
Related to offsetting interest rate swaps.
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount
Compensation and Employee Benefit Plans, Other than Share-Based Compensation [Text Block]
us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)
Deferred tax asset
Share-Based Payment Arrangement [Text Block]
Other assets
Other Assets
Award Type [Domain]
Provision for other real estate owned
Represents the provision for other real estate owned.
Award Type [Axis]
us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Accumulated amortization
us-gaap_FiniteLivedIntangibleAssetsNet
Finite-Lived Intangible Assets, Net
us-gaap_LifeSettlementContractsFairValueMethodGainLoss
Gain on BOLI death benefit proceeds
Standby Letters of Credit [Member]
Gross carrying amount
Loss Contingency, Nature [Domain]
Trademark intangible
Indefinite-Lived Trademarks
Loss Contingency Nature [Axis]
Bank Servicing [Member]
Bank premises and equipment, accumulated depreciation
Commitments and Contingencies Disclosure [Text Block]
Bank premises and equipment, net of accumulated depreciation of $23,836 and $21,853, respectively
us-gaap_Goodwill
Goodwill
Bank premises and equipment, gross
Property, Plant and Equipment, Gross
Interest rate swaps
Derivative Liabilities
us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue
Net change in value of BOLI
Interest rate swaps
Derivative Assets
istr_DebtSecuritiesHeldtomaturityFairValueDisclosure
Investment securities - HTM
Fair value of investment in debt security measured at amortized cost (held-to-maturity).
Interest rate swaps - gross assets
us-gaap_DerivativeAssets
us-gaap_DebtSecurities
Debt Securities
Derivative Instrument [Axis]
Derivative Contract [Domain]
us-gaap_IncomeLossFromEquityMethodInvestments
Equity in undistributed earnings of bank subsidiary
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Investment in bank subsidiary
Income tax expense
Total income tax expense
Income tax benefit
Transfer of Financial Assets Accounted for as Sales [Table]
Commitments to extend credit
us-gaap_UnusedCommitmentsToExtendCredit
us-gaap_MortgageLoansInProcessOfForeclosureAmount
Mortgage Loans in Process of Foreclosure, Amount
us-gaap_OtherRealEstateDisposals
Sales of other real estate owned
Other Real Estate, Roll Forward [Table Text Block]
Additions
Other expense
us-gaap_OperatingExpenses
Total expense
us-gaap_DefinedContributionPlanCostRecognized
Defined Contribution Plan, Cost
istr_GainLossOnSalesOfForeclosedAssets
(Gain) loss on sale of other real estate owned, net
The net gain (loss) resulting from sales and other disposals of assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceeding or defeasance; excludes write-downs.
istr_FederalHomeLoanBankStockDividends
FHLB stock dividend
Dividends received on federal home loan bank stock.
us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Defined Contribution Plan, Employer Discretionary Contribution Amount
Distributions from investments
Amount of distribution received from investments.
us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay
Net amortization (accretion) of purchase accounting adjustments
The expense charged against earnings for the periodic recognition of purchase accounting adjustments.
us-gaap_GeneralInsuranceExpense
General Insurance Expense
Corporate Stock and Mutual Funds [Member]
Represents the corporate stock and mutual funds.
Interest-bearing balances due from other banks
Due within one year, HTM, fair value
Due after one year through five years, HTM, fair value
Due after five years through ten years, HTM, fair value
Due after ten years, HTM, fair value
us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
Gross Unrealized Losses
Gross Unrealized Gains
us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
Salaries and employee benefits
istr_PolicyTable
Cash and due from banks
Nature of Operations Policy [Policy Text Block]
Disclosure of accounting policy for nature of operations.
One to Four Family Residential Property [Member]
Represents 1-4 family residential property.
istr_DerivativeCollateralPost
Derivative, Collateral Post
Amount of collateral post for derivative activities as of balance sheet date.
Real Estate Owned [Text Block]
Amendment Flag
istr_NetIncomeLossAllocatedToCommonStockholdersBasic
Net income allocated to common shareholders
Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.
City Area Code
Use of Estimates, Policy [Policy Text Block]
Brokered demand deposits
Amount of interest-bearing domestic third-party demand deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.
New Accounting Pronouncements, Policy [Policy Text Block]
Non-employee Directors and Certain Officers [Member]
Represents non-employee directors and certain officers.
istr_OtherRealEstateOwnedWriteDowns
Other Real Estate Owned, Write Downs
Write-downs
Represents the amount of write downs on other real estate owned during the period.
Brokered time deposits
Amount of interest-bearing domestic third-party time deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.
(Loss) gain on sale or disposition of fixed assets, net
Gain (Loss) on Disposition of Property Plant Equipment
Loss (gain) on sale or disposition of fixed assets, net
Customers [Member]
Represents customers.
W F B [Member]
Represents WFB.
Off-Balance-Sheet, Allowance for Credit Loss [Table Text Block]
Tabular disclosure of of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.
Gain (loss) on sale of other real estate owned, net
Other Financial Institutions [Member]
Represents other financial institutions.
Gain on sale of loans
Gain on sale of loans
Current Fiscal Year End Date
us-gaap_NotesReceivableNet
Financing Receivable, after Allowance for Credit Loss
Accrued interest receivable
Interest Receivable
Document Fiscal Period Focus
Gain (loss) on call or sale of investment securities, net
(Gain) loss on call or sale of investment securities, net
Document Fiscal Year Focus
Consolidation, Policy [Policy Text Block]
Document Period End Date
Entity File Number
Tier 1 leverage capital, actual ratio
Entity Emerging Growth Company
Tier 1 leverage capital, well capitalized ratio
Document Type
us-gaap_GainsLossesOnExtinguishmentOfDebt
Gain on early extinguishment of subordinated debt
Total risk-based capital, well capitalized ratio
Entity Small Business
Income from legal settlement
Entity Shell Company
Common Equity Tier 1 risk-based capital, actual ratio
Document Information [Line Items]
Document Information [Table]
Total risk-based capital, actual ratio
Entity Public Float
Entity Filer Category
Tier 1 risk-based capital, actual ratio
Entity Current Reporting Status
Entity Voluntary Filers
Acquisition expense
Tier 1 risk-based capital, well capitalized ratio
Entity Well-known Seasoned Issuer
Total risk-based capital, actual amount
Total risk-based capital, well capitalized amount
Bank owned life insurance
Award Timing MNPI Disclosure [Text Block]
Tier 1 leverage capital, actual amount
istr_LoanParticipationsAndWholeLoansSoldToAndServicedForOthersNotOnBalanceSheet
Loan Participations and Whole Loans Sold to and Serviced for Others Not on Balance Sheet
Principal balance on loan participations and whole loans sold and serviced for others that is excluded from the balance sheet.
istr_LoanParticipationsAndWholeLoansSoldToAndServicedForOthersUnpaidPrincipalBalance
Loan Participations and Whole Loans Sold to and Serviced For Others Unpaid Principal Balance
Unpaid principal balance on loan participations and whole loans sold and serviced for others, including the portion that was sold and not reflected on the balance sheet.
Tier 1 leverage capital, well capitalized amount
Debt Securities, Held-to-Maturity [Table Text Block]
Statement of Other Comprehensive Income [Abstract]
Common Equity Tier 1 risk-based capital, actual amount
Statement of Comprehensive Income [Abstract]
ecd_AwardTmgMnpiCnsdrdFlag
Award Timing MNPI Considered [Flag]
Debt Securities, Held-to-Maturity [Table]
Entity Tax Identification Number
Common Equity Tier 1 risk-based capital, well capitalized amount
Entity Central Index Key
Depreciation and amortization
Depreciation, Depletion and Amortization, Nonproduction
Insider Trading Policies and Procedures [Line Items]
Tier 1 risk-based capital, actual amount
Entity Registrant Name
ecd_InsiderTrdPoliciesProcAdoptedFlag
Insider Trading Policies and Procedures Adopted [Flag]
Tier 1 risk-based capital, well capitalized amount
Entity [Domain]
Legal Entity [Axis]
Real Estate Portfolio Segment [Member]
Portfolio segment of the company's total financing receivables related to real estate.
Entity Address, Address Line One
1-4 Family [Member]
Represents the 1-4 family real estate loans.
us-gaap_AmortizationOfIntangibleAssets
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]
Entity Address, Postal Zip Code
Regulatory Capital Requirements under Banking Regulations [Text Block]
Multifamily Loans [Member]
Represents multifamily loans.
us-gaap_OtherRealEstate
Balance, beginning of period
Balance, end of period
Farmland [Member]
Represents farmland loans.
Entity Address, State or Province
ecd_NonRule10b51ArrAdoptedFlag
Non-Rule 10b5-1 Arrangement Adopted [Flag]
Commercial Real Estate Loan [Member]
Represents the commercial real estate loan.
Material Terms of Trading Arrangement [Text Block]
Other real estate owned, net
Repossessed Assets
ecd_TrdArrIndTitle
Trading Arrangement, Individual Title
ecd_TrdArrIndName
Trading Arrangement, Individual Name
istr_PreferredStockConvertibleForcedConversionTriggerPrice
Preferred Stock, Convertible, Forced Conversion Trigger Price (in dollars per share)
Represents the trigger price for forced conversion of convertible preferred stock.
ecd_TrdArrTerminationDate
Trading Arrangement Termination Date
ecd_TrdArrSecuritiesAggAvailAmt
Trading Arrangement, Securities Aggregate Available Amount
Entity Common Stock, Shares Outstanding
Trading Arrangements, by Individual [Table]
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
ecd_TrdArrAdoptionDate
Trading Arrangement Adoption Date
Professional fees
Marketing
Trading Symbol
Data processing
Occupancy
Occupancy, Net
Local Phone Number
us-gaap_TableTextBlock
Notes Tables
2025, weighted average rate
2026, weighted average rate
Real Estate Owned, Valuation Allowance, Policy [Policy Text Block]
2028, weighted average rate
Restricted Stock and Restricted Stock Units [Member]
Represents restricted stock and restricted stock units.
us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate
2026
us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate
2028
us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds
Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds
Fair Value
Held to maturity securities, fair value
Total debt securities, HTM, fair value
us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged
us-gaap_CashCashEquivalentsAndFederalFundsSold
Cash and cash equivalents
Forward Starting Interest Rate Swap [Member]
Derivative contracts where two parties agree to exchange a fixed or floating rate cash flow for the other over a period of time.
Weighted average rate
Schedule of Investments [Table]
Amortization of subordinated debt issuance costs
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Subsequent Event [Member]
Interest on borrowings
Goodwill and other intangible assets, net
Intangible Assets, Net (Including Goodwill)
Subsequent Event [Table]
Subsequent Event Type [Axis]
Impaired loans, measurement input
istr_ImpairedFinancingReceivableMeasurementInput
Value of input used to measure impaired financing receivable.
Defined Benefit Plan [Table]
Subsequent Event Type [Domain]
Measurement Input, Collateral Discounts and Estimated Costs to Sell [Member]
Represents the measurement input as collateral discounts and estimated costs to sell.
Subsequent Events [Text Block]
Deposits, interest-bearing
istr_InterestBearingDepositLiabilitiesFairValueDisclosure
The fair value portion of interest bearing deposit liabilities.
Deposits, noninterest-bearing
istr_NoninterestBearingDepositLiabilitiesFairValueDisclosure
The fair value portion of noninterest bearing deposit liabilities.
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive
Thereafter
us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedAsset
Total, offset
us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
Deferred Compensation Arrangement with Individual, Compensation Expense
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
2027
Interest on deposits
us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimCash
Total, not offset, cash collateral
istr_NumberOfBankBranchesClosed
Number of Bank Branches Closed
The number of bank branches closed.
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2028
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
2029
Cheaha Statutory Trust I [Member]
Represents Cheaha Statutory Trust I.
Salaries and Employee Benefits [Member]
Represents salaries and employee benefits.
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive
2030
us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedGross
Total
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]
Segment Reporting, Policy [Policy Text Block]
us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
2026
us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities
Total, not offset by financial instruments
Tier 1 leverage capital, capital adequacy amount
Amount of minimum Tier 1 leverage capital required for capital adequacy as defined by regulatory framework including conservation buffer.
Common Equity Tier 1 risk-based capital, capital adequacy amount
Amount of minimum Common Equity Tier 1 risk-based capital required for capital adequacy as defined by regulatory framework including conservation buffer.
Tier 1 risk-based capital, capital adequacy amount
Amount of minimum Tier 1 risk-based capital required for capital adequacy as defined by regulatory framework including conservation buffer.
Total risk-based capital, capital adequacy amount
Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework including conservation buffer.
us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1
Finite-Lived Intangible Assets, Remaining Amortization Period (Year)
us-gaap_DeferredCompensationArrangementWithIndividualMaximumContractualTerm1
Deferred Compensation Arrangement with Individual, Maximum Contractual Term (Month)
istr_CommitmentToFundInvestmentInSBICQualifiedFunds
Commitment to Fund Investment in SBIC Qualified Funds
Unfunded commitments to investment in Small Business Investment Company qualified funds.
Business Combination [Policy Text Block]
us-gaap_FiniteLivedIntangibleAssetUsefulLife
Finite-Lived Intangible Asset, Useful Life (Year)
Earnings Per Share, Policy [Policy Text Block]
Tier 1 leverage capital, capital adequacy ratio
Ratio of minimum Tier 1 leverage capital to average assets required for capital adequacy as defined by regulatory framework including conservation buffer.
Common Equity Tier 1 risk-based capital, capital adequacy ratio
Ratio of minimum Common Equity Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework including conservation buffer.
INTEREST EXPENSE
Tier 1 risk-based capital, capital adequacy ratio
Ratio of minimum Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework inclusing conservation buffer.
Total risk-based capital, capital adequacy ratio
Ratio of minimum total risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework including conservation buffer.
us-gaap_Revenues
Total revenue
us-gaap_RevenuesNetOfInterestExpense
Income before noninterest expense
EXPENSE
Comprehensive Income, Policy [Policy Text Block]
Intangible Asset, Finite-Lived [Table]
Income Tax, Policy [Policy Text Block]
Interest income from investment in trust
Dividends on corporate stock
us-gaap_InterestAndDividendIncomeOperating
Total interest income
Schedule of Finite-Lived Intangible Assets [Table Text Block]
Current-period gross charge-offs, revolving
us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff
Current-period gross charge-offs, year four
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff
Current-period gross charge-offs, year five
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff
Current-period gross charge-offs, prior
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff
us-gaap_SharesIssuedPricePerShare
Shares Issued, Price Per Share (in dollars per share)
Current-period gross charge-offs, year three
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff
Current-period gross charge-offs, current year
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff
Share-Based Payment Arrangement [Policy Text Block]
Equity [Text Block]
Current-period gross charge-offs, year two
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff
us-gaap_TimeDepositMaturitiesYearFour
2029
Interest on investment securities
us-gaap_TimeDepositMaturitiesYearFive
2030
Taxable
Tax-exempt
us-gaap_TimeDepositMaturitiesYearOne
2026
us-gaap_TimeDepositMaturitiesYearTwo
2027
us-gaap_TimeDepositMaturitiesYearThree
2028
Other interest income
Interest and fees on loans
Stockholders' Equity, Policy [Policy Text Block]
INTEREST INCOME
us-gaap_DeferredTaxAssetsLiabilitiesNet
Net deferred tax asset
Time deposits
Money market deposits
Other
us-gaap_DeferredTaxAssetsOther
Savings deposits
Goodwill and Intangible Assets, Policy [Policy Text Block]
us-gaap_DeferredTaxAssetsGross
Gross deferred tax asset
us-gaap_DeferredIncomeTaxLiabilities
Gross deferred tax liability
Interest-bearing demand deposits
Other operating income
Noninterest Income, Other Operating Income
us-gaap_NoninterestIncome
Total noninterest income
Unrealized loss on AFS securities
Income from bank owned life insurance
Deposit Liabilities Disclosures [Text Block]
NONINTEREST INCOME
Reversal of credit losses
Provision for Loan, Lease, and Other Losses
us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss
Net interest income after reversal of credit losses
Cumulative Effect, Period of Adoption [Domain]
Software and Software Development Costs [Member]
Cumulative Effect, Period of Adoption [Axis]
us-gaap_PropertyPlantAndEquipmentUsefulLife
Property, Plant and Equipment, Useful Life (Year)
Cumulative Effect, Period of Adoption, Adjustment [Member]
us-gaap_InterestIncomeExpenseNet
Net interest income
Construction in Progress [Member]
us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses
Allowance for credit losses
Furniture and Fixtures [Member]
us-gaap_NumberOfReportableSegments
Number of Reportable Segments
Employee and director stock awards
Building and Building Improvements [Member]
Deferred compensation
Building [Member]
REVENUE
Building Improvements [Member]
Land [Member]
Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block]
Property, Plant and Equipment, Policy [Policy Text Block]
Property, Plant and Equipment [Table]
Long-Lived Tangible Asset [Axis]
Long-Lived Tangible Asset [Domain]
Deposit Account [Member]
Credit and Debit Card [Member]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
Cash and cash equivalents, beginning of period
Cash and cash equivalents, end of period
Assets [Abstract]
Private Placement [Member]
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect
Net increase (decrease) in cash and cash equivalents
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net cash provided by (used in) financing activities
Sale of Stock [Axis]
Director [Member]
Transfers and Servicing of Financial Assets, Transfers of Financial Assets, Policy [Policy Text Block]
Sale of Stock [Domain]
Other operating income
us-gaap_OtherOperatingIncome
us-gaap_NetCashProvidedByUsedInOperatingActivities
Net cash provided by operating activities
us-gaap_DeferredTaxLiabilitiesOther
Other
us-gaap_NetCashProvidedByUsedInInvestingActivities
Net cash (used in) provided by investing activities
FHLB long-term advances
istr_FederalHomeLoanBankLongTermBorrowingsFairValueDisclosure
Fair value portion of long-term borrowing from Federal Home Loan Bank (FHLBank).
Derivatives, Policy [Policy Text Block]
us-gaap_BankingRegulationCapitalConservationBufferCapitalConservedMinimum
Banking Regulation, Capital Conservation Buffer, Capital Conserved, Minimum
Due after ten years, HTM, amortized cost
us-gaap_DeferredTaxLiabilitiesLeasingArrangements
Operating lease ROU asset
Repurchase Agreements, Valuation, Policy [Policy Text Block]
Due after five years through ten years, HTM, amortized cost
Due after one year through five years, HTM, amortized cost
Common Equity Tier 1 risk-based capital, well capitalized ratio
Investment, Policy [Policy Text Block]
Due within one year, HTM, amortized cost
Marketable Securities, Policy [Policy Text Block]
Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block]
us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment
Depreciation
us-gaap_PaymentsOfDividendsCommonStock
Cash dividends paid on common stock
us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
Cash dividends paid on preferred stock
Financing Receivable, Credit Ratio [Table]
Other operating expenses
us-gaap_NoninterestExpense
Total noninterest expense
us-gaap_DerivativeAssetSecurityPurchasedUnderAgreementToResellSecurityBorrowedAfterOffsetAndDeductionSubjectToMasterNettingArrangement
Total, net
us-gaap_PaymentsForRepurchaseOfCommonStock
Payments to repurchase common stock
us-gaap_DerivativeAssetSecurityPurchasedUnderAgreementToResellSecurityBorrowedAfterOffsetSubjectToMasterNettingArrangement
Total, net amounts in Balance Sheet
Interest rate swaps, net
us-gaap_DerivativeAssetFairValueAfterOffsetAndDeductionSubjectToMasterNettingArrangement
us-gaap_ProceedsFromIssuanceOfPrivatePlacement
Proceeds from Issuance of Private Placement
Noninterest income
Proceeds from stock options exercised
Title and Position [Domain]
Current state income tax expense
Title and Position [Axis]
Proceeds from preferred stock offering, net of issuance costs
NONINTEREST EXPENSE
Interest rate swaps, net
us-gaap_DerivativeLiabilityFairValueAfterOffsetAndDeductionSubjectToMasterNettingArrangement
Accounting Standards Update 2016-13 [Member]
Current federal income tax expense
Deferred federal income tax expense
us-gaap_DerivativeLiabilitySecuritySoldUnderAgreementToRepurchaseSecurityLoanedAfterOffsetSubjectToMasterNettingArrangement
Total, net amounts in Balance Sheet
Unfunded Loan Commitment [Member]
us-gaap_DerivativeLiabilitySecuritySoldUnderAgreementToRepurchaseSecurityLoanedAfterOffsetAndDeductionSubjectToMasterNettingArrangement
Total, net
Class of Financing Receivable [Domain]
Construction Loans [Member]
Class of Financing Receivable [Axis]
Financing Receivable Portfolio Segment [Domain]
us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Income before income tax expense
Commercial Portfolio Segment [Member]
Consumer Portfolio Segment [Member]
Financing Receivable Portfolio Segment [Axis]
us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss
ICFR Auditor Attestation Flag
us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Income Tax Jurisdiction [Axis]
Income Tax Jurisdiction [Domain]
Domestic Tax Jurisdiction [Member]
Financing Receivable [Policy Text Block]
Recoveries
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Recovery
Current-period gross charge-offs, Total
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Charge-offs
us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecovery
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff (Recovery)
us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings
Repayment of long-term FHLB advances
Cash and Cash Equivalents, Policy [Policy Text Block]
Reversal of credit losses on loans
Financing Receivable, Excluding Accrued Interest, Credit Loss Expense (Reversal)
Nonaccrual loans
us-gaap_RepaymentsOfSubordinatedDebt
Extinguishment of subordinated debt
Nonaccrual with no allowance
Schedule of Subordinated Borrowing [Table Text Block]
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]
Basis of Accounting, Policy [Policy Text Block]
Subordinated Borrowings Disclosure [Text Block]
Common Stock Dividends per share declared (in dollars per share)
Proceeds from long-term FHLB advances
Condensed Financial Information of Parent Company Only Disclosure [Text Block]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
Accounts and Financing Receivables [Table]
Auditor Name
Auditor Firm ID
Auditor Location
Pledging Purpose [Domain]
Antidilutive Securities (in shares)
us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Weighted average diluted shares outstanding (in shares)
Net (decrease) increase in borrowings under the BTFP
Pledging Purpose [Axis]
ROU assets
us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]
us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss
Financing Receivable, Accrued Interest, after Allowance for Credit Loss
Statement of Financial Position [Abstract]
Diluted earnings per common share (in dollars per share)
Diluted earnings per common share (in dollars per share)
Weighted average basic shares outstanding (in shares)
us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Other, percent
us-gaap_EffectiveIncomeTaxRateContinuingOperations
Total income tax expense and effective tax rate, as reported, percent
Business Combination [Axis]
Basic earnings per common share (in dollars per share)
Basic earnings per common share (in dollars per share)
Credit Loss, Financial Instrument [Policy Text Block]
Business Combination [Domain]
Statement of Cash Flows [Abstract]
Statement of Stockholders' Equity [Abstract]
us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome
Tax-exempt interest, percent
Preferred Stock Dividends per share declared (in dollars per share)
Net increase (decrease) in repurchase agreements
Repurchase agreements, net
us-gaap_LesseeOperatingLeaseRemainingLeaseTerm
Lessee, Operating Lease, Remaining Lease Term (Year)
Financing Receivable, Nonaccrual [Table Text Block]
Repurchase agreements, net amounts in Balance Sheet
us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Business Combination, Consideration Transferred, Equity Interest, Share Issued, Number of Shares (in shares)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table]
Investments Classified by Contractual Maturity Date [Table Text Block]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]
us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseLifeInsurance
BOLI impact, percent
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
Other, percent
us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Net increase in customer deposits
Schedule of Available-for-Sale Securities Reconciliation [Table Text Block]
Share Repurchase Program [Table]
us-gaap_LoansAndLeasesReceivableRelatedParties
Loans and Leases Receivable, Related Parties
Balance, beginning of period
Balance, end of period
State taxes, net of federal income tax effects, percent
Other
Cash flows from financing activities
Federal income tax based on statutory rate, 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]
Dividend payable
Asset Not Pledged as Collateral and Asset Pledged as Collateral without Right [Member]
us-gaap_IncomeTaxReconciliationTaxExemptIncome
Tax-exempt interest
Debt Securities, Held-to-Maturity, Past Due [Table]
us-gaap_PaymentsToAcquireLifeInsurancePolicies
Purchases of BOLI
Proceeds from surrender of BOLI
istr_DeferredTaxLiabilitiesFederalHomeLoanBankStockDividend
FHLB stock dividend
Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.
istr_DeferredTaxLiabilitiesBasisDifferenceInAcquiredAssetsAndLiabilities
Basis difference in acquired assets and liabilities
Amount of deferred tax liability attributable to taxable temporary differences in acquired assets and liabilities.
Series A Preferred Stock [Member]
istr_DefinedBenefitPlanEligibilityForParticipationRequisiteAgeOfEmployees
Defined Benefit Plan, Eligibility For Participation Requisite Age Of Employees (Year)
Eligibility for participation requisite age of employees of defined benefit plan.
istr_MinimumServicePeriodForParticipationInDefinedBenefitPlan
Minimum Service Period for Participation in Defined Benefit Plan (Month)
Represents minimum service period for participation in defined benefit plan.
istr_DefinedContributionPlanEmployersDiscretionaryContributionAnnualVestingPercentage
Defined Contribution Plan, Employers Discretionary Contribution, Annual Vesting Percentage
Represents annual vesting percentage of employers discretionary contribution for defined contribution plan.
istr_DefinedContributionPlanEmployerDiscretionaryContributionAmountAwardVestingPeriod
Defined Contribution Plan, Employer Discretionary Contribution Amount, Award Vesting Period (Year)
Represents award vesting period of employer discretionary of defined contribution amount for defined contribution plan.
Cash paid for branch sale to First Community Bank, net of cash received
Pledged Status [Domain]
Basis difference in acquired assets and liabilities
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from basis difference in acquire assets and liabilities.
Pledged Status [Axis]
Operating lease liability
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from operating lease liability.
Unearned loan fees
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from unearned loan fees.
istr_DeferredCompensationArrangementWithIndividualMonthlyDistribution
Deferred Compensation Arrangement With Individual, Monthly Distribution
Represents monthly distribution for deferred compensation arrangement with individual.
us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Bank premises and equipment, net
us-gaap_IncomeTaxReconciliationNondeductibleExpenseLifeInsurance
BOLI impact
A 2017 Long Term Incentive Compensation Plan [Member]
Represents a 2017 Long-Term Incentive Compensation Plan.
us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization
Less: accumulated depreciation and amortization
us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries
Investment in subsidiary
Other
us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther
Key Personnel [Member]
Represents key personnel.
istr_DefinedContributionPlanAwardRequisiteServicePeriod
Defined Contribution Plan, Award Requisite Service Period (Year)
Award Requisite period for defined contribution plan.
Class of Stock [Axis]
istr_DefinedContributionPlanEmployerDiscretionaryContributionAmountTotalAwardVestingPeriod
Defined Contribution Plan, Employer Discretionary Contribution Amount Total Award Vesting Period (Year)
Represents award vesting period for employer discretionary contribution amount of defined contribution plan.
Class of Stock [Domain]
istr_DeferredCompensationArrangementWithIndividualRequisiteAgeOfEmployees
Deferred Compensation Arrangement With Individual, Requisite Age Of Employees (Year)
Requisite age of employees for defined compensation arrangement with individual.
istr_DeferredCompensationArrangementWithIndividualReducedPaymentsMaximumAgeUponTermination
Deferred Compensation Arrangement With Individual, Reduced Payments, Maximum Age Upon Termination (Year)
Maximum age upon termination for reduced payments of deferred compensation arrangement with individual.
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
us-gaap_PaymentsToAcquireBusinessesGross
Payments to Acquire Businesses, Gross
First Community Louisiana Statutory Trust I [Member]
Represents First Community Louisiana Statutory Trust I.
Amortized Cost
Available for sale, Amortized cost
Total debt securities, AFS, amortized cost
BOJ Bancshares Statutory Trust I [Member]
Represents BOJ Bancshares Statutory Trust I.
Employees [Member]
Represents information related to employees.
Employees and Directors [Member]
Represents employees and directors.
us-gaap_PaymentsForProceedsFromLoansReceivable
Net (increase) decrease in loans
State taxes, net of federal income tax effects
Notional
Derivative, Notional Amount
Federal income tax based on statutory rate
Hedging Relationship [Domain]
Fair Value
Available for sale securities at fair value (amortized cost of $416,002 and $392,564, respectively)
Debt Securities, Available-for-Sale, Excluding Accrued Interest
Total debt securities, AFS, fair value
Cash Flow Hedging [Member]
Hedging Relationship [Axis]
Income Tax Disclosure [Text Block]
us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss
Total debt securities, HTM, amortized cost
Derivative Instruments and Hedging Activities Disclosures [Table]
Amortized Cost
Held to maturity securities at amortized cost (estimated fair value of $50,540 and $42,144, respectively)
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
Pass [Member]
Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
Proceeds from maturities, prepayments and calls of investment securities held to maturity
us-gaap_GoodwillAndIntangibleAssetImpairment
Goodwill and Intangible Asset Impairment, Total
Proceeds from sales
Proceeds from sales of investment securities available for sale
Internal Credit Assessment [Axis]
Proceeds from maturities, prepayments and calls of investment securities available for sale
Internal Credit Assessment [Domain]
us-gaap_PaymentsToAcquireOtherInvestments
Purchases of other investments
Proceeds from sales of other real estate owned
Equity securities at fair value
us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent
Equity securities at fair value
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]
us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt
Purchases of securities available for sale
us-gaap_PaymentsToAcquireHeldToMaturitySecurities
Purchases of securities held to maturity
us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Less: allowance for credit losses
Balance, beginning of period
Balance, end of period
Financial Asset, Not Past Due [Member]
Goodwill and Intangible Assets Disclosure [Text Block]
us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss
Loans, net
Secured Debt [Member]
Proceeds from sales of fixed assets
Loans
Loans
us-gaap_FinancingReceivableDeferredIncome
Financing Receivable, Deferred Commitment Fee
Year five
us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear
Special Mention [Member]
Year four
us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear
Substandard [Member]
Financing Receivable, Nonaccrual [Table]
Current year
us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear
Year three
us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear
us-gaap_PaymentsToAcquireOtherProductiveAssets
Purchases of fixed assets
Prior
us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Revolving
us-gaap_FinancingReceivableExcludingAccruedInterestRevolving
Year two
us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear
Dilutive effect of stock-based compensation (in shares)
Transfer from loans to other real estate owned
Dilutive effect of Series A Preferred Stock (in shares)
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING ACTIVITIES
Change in the fair value of equity securities
Change in the fair value of equity securities
us-gaap_FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount
Financing Receivable, Unamortized Loan Cost (Fee) and Purchase Premium (Discount)
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
FHLB short-term advances and repurchase agreements
FHLB short-term advances and repurchase agreements
us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Net income available to common shareholders
us-gaap_OperatingLeaseLeaseIncome
Operating Lease, Lease Income
Core Deposits [Member]
us-gaap_OperatingLeaseIncomeComprehensiveIncomeExtensibleList
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]
Finite-Lived Intangible Assets by Major Class [Axis]
Finite-Lived Intangible Assets, Major Class Name [Domain]
us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation
Surrendered shares
Equity in undistributed earnings of bank subsidiary
Preferred stock dividends declared
Effective Income Tax Rate Reconciliation [Table]
Advances from Federal Home Loan Bank
Advance from Federal Home Loan Bank
Net income
Net income (loss)
Net income
Financial Instrument Performance Status [Axis]
Financial Instrument Performance Status [Domain]
Nonperforming Financial Instruments [Member]
Restricted Stock Units (RSUs) [Member]
Financing Receivable Credit Quality Indicators [Table Text Block]
Proceeds from BOLI death benefits
us-gaap_PaymentsToAcquireEquitySecuritiesFvNi
Purchases of equity securities at fair value
Share-Based Payment Arrangement, Option [Member]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]
Financial Asset, 30 to 59 Days Past Due [Member]
Antidilutive Security, Excluded EPS Calculation [Table]
Financial Asset, 60 to 89 Days Past Due [Member]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Table Text Block]
Financing Receivable, Past Due [Table]
Financial Asset, Aging [Axis]
us-gaap_PreferredStockConvertibleConversionRatio
Preferred Stock, Convertible, Conversion Ratio
Financial Asset, Aging [Domain]
Proceeds from redemption or sale of equity securities at fair value
us-gaap_PaymentsToAcquireLoansHeldForInvestment
Purchases of loans
istr_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1
Less than 12 months, unrealized losses
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.
Long-Term Debt, Type [Axis]
Less than 12 months, fair value
istr_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPositionLessThan12MonthsFairValue1
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months.
Long-Term Debt, Type [Domain]
istr_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss1
12 months or more, unrealized losses
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.
12 months or more, fair value
istr_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue1
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.
Earnings Per Share, Diluted, by Common Class, Including Two-Class Method [Table]
istr_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLoss1
Total, unrealized losses
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
Total, fair value
istr_DebtSecuritiesHeldtomaturityUnrealizedLossPositionFairValue1
Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.
Greater Than Ninety Days and Accruing [Member]
Relating to greater than 90 days and accruing.
us-gaap_RelatedPartyDepositLiabilities
Related Party Deposit Liabilities
us-gaap_FederalHomeLoanBankAdvances
Federal Home Loan Bank, Advance
Less: income allocated to participating securities
Cash flows from investing activities
Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table]
Bank Term Funding Program [Member]
Relating to the Bank Term Funding Program.
EARNINGS PER COMMON SHARE
Earnings Per Share [Text Block]
London Interbank Offer Rate [Member]
Relating to the London Interbank Offered Rate.
Related Party Transaction [Table]
Related Party Transactions Disclosure [Text Block]
Accrued other liabilities
Accrued taxes and other liabilities
Schedule of Related Party Transactions [Table Text Block]
Federal Home Loan Bank, Advances [Table Text Block]
Reclassification of realized gain, tax
Unrealized gain (loss) available for sale, tax
State
Federal
Unrealized (loss) gain included in other comprehensive loss
Subordinated Debt [Member]
us-gaap_InterestExpenseOperating
Total interest expense
us-gaap_AllocatedShareBasedCompensationExpense
Share-Based Payment Arrangement, Expense
Realized gain (loss) included in net income
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings
Loans individually evaluated for impairment
Balance of loans individually evaluated for impairment
Balance of loans collectively evaluated for impairment
Ending allowance balance for loans individually evaluated for impairment
Ending allowance balance for loans collectively evaluated for impairment
us-gaap_ComprehensiveIncomeNetOfTax
Total comprehensive income
Provision for (reversal of) credit losses on unfunded loan commitments
Debt Securities, Held-to-Maturity, Unrealized Loss Position, Fair Value [Table Text Block]
Tabular disclosure of fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (held-to-maturity), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
us-gaap_OffBalanceSheetCreditLossLiability
Balance, beginning of period
Balance, end of period
Common stock, shares outstanding (in shares)
Common Stock, Shares, Outstanding (in shares)
Preferred stock, shares outstanding (in shares)
Preferred Stock, Shares Outstanding (in shares)
Financing Receivable, Allowance for Credit Loss [Table Text Block]
Financing Receivable, Allowance for Credit Loss [Table]
us-gaap_IncreaseDecreaseInOtherOperatingAssets
Other assets
Variable Interest Rate
Debt Instrument, Basis Spread on Variable Rate
Interest rate
Debt Instrument, Interest Rate, Stated Percentage
Statement Of Other Comprehensive Income Abstract [Domain]
Weighted average discount rate
Total operating lease cost
us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Deferred tax liability
Lease, Cost [Table Text Block]
us-gaap_DebtInstrumentRepurchasedFaceAmount
Debt Instrument, Repurchased Face Amount
Weighted average remaining lease term (in years) (Year)
us-gaap_DebtInstrumentFaceAmount
Debt Instrument, Face Amount
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
us-gaap_DividendsCommonStockCash
Common stock dividends declared
Capitalization, Equity [Table]
istr_PreferredStockConvertibleThresholdTradingDays
Preferred Stock, Convertible, Threshold Trading Days
Threshold number of specified trading days that common stock price to conversion price of convertible preferred stock must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.
us-gaap_DividendsPreferredStock
Preferred stock dividends declared, $32.50 per share
istr_PreferredStockConvertibleThresholdConsecutiveTradingDays
Preferred Stock, Convertible, Threshold Consecutive Trading Days
Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible preferred stock must exceed threshold percentage for specified number of trading days to trigger conversion feature.
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet
Accrued interest receivable
Variable Rate [Domain]
Schedule of Long-Term Debt Instruments [Table]
Variable Rate [Axis]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Balance
Balance
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Transfers into level 3
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Transfers out of level 3
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Purchases
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Sales
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Maturities, prepayments, and calls
Depreciation and Amortization [Member]
Represents depreciation and amortization.
us-gaap_StockRepurchasedDuringPeriodShares
Stock Repurchased During Period, Shares (in shares)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Shares repurchased
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Offsetting Assets and Liabilities [Table Text Block]
Tabular disclosure of derivative and other financial assets and liabilities that are subject to offsetting, including master netting arrangements.
Bank Premises and Equipment [Member]
Represents bank premises and equipment.
us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Exercised, shares (in shares)
istr_FinancingReceivableImpairedDuringPeriodAllowanceForCreditLossesIndividuallyEvaluatedForImpairment
Financing Receivable, Impaired During Period, Allowance For Credit Losses, Individually Evaluated For Impairment
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment during the period.
us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Line of Credit Facility, Current Borrowing Capacity
Options exercised
Stock-based compensation
Granted, shares (in shares)
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares)
us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
Forfeited, shares (in shares)
Line of Credit Facility, Lender [Domain]
Other Real Estate Owned, Measurement Input
us-gaap_StockIssuedDuringPeriodSharesNewIssues
Stock Issued During Period, Shares, New Issues (in shares)
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Lender Name [Axis]
us-gaap_LiabilitiesAndStockholdersEquity
Total liabilities and stockholders’ equity
Reported Value Measurement [Member]
Preferred stock issuance, net of issuance costs
Asset Pledged as Collateral [Member]
Retained earnings
Accumulated other comprehensive loss
Short-Term Debt [Table]
Debt Disclosure [Text Block]
Net change in:
Total lease obligations
Operating Lease, Liability
us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList
Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration]
Other Real Estate Owned, Fair Value Disclosure
istr_OtherRealEstateOwnedFairValueDisclosure
Other Real Estate Owned, Fair Value Disclosure
The fair value amount of other real estate owned.
us-gaap_OperatingLeaseRightOfUseAsset
Operating Lease, Right-of-Use Asset
us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue
Total lease payments
us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount
Less: imputed interest
Deferred taxes
2028
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree
Measurement Input Type [Axis]
Measurement Input, Collateral Discounts and Discount Rates [Member]
Represents the measurement input as collateral discounts and discount rates.
Cheaha Financial Group [Member]
Information related to Cheaha Financial Group, Inc. (“Cheaha”).
2029
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour
Measurement Input Type [Domain]
2030
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive
Measurement Input, Appraised Value [Member]
Investment securities, measurement input
us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput
Accrued Taxes and Other Liabilities [Member]
Information related to accrued taxes and other liabilities.
Thereafter
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive
Net Investment in Lease, before Allowance for Credit Loss
Valuation Technique, Discounted Cash Flow [Member]
2026
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths
Debt Securities, Available-for-Sale [Table Text Block]
2027
us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo
Valuation Approach and Technique [Axis]
Valuation Approach and Technique [Domain]
us-gaap_StockOptionPlanExpense
Stock or Unit Option Plan Expense
Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]
us-gaap_ShareBasedCompensation
Stock-based compensation
Total assets
us-gaap_AssetsFairValueDisclosure
us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments
Net accretion of securities
Equity securities at fair value
us-gaap_EquityFairValueDisclosure
us-gaap_TradingSecurities
Debt Securities, Trading, and Equity Securities, FV-NI
Equity securities at fair value
Equity Securities, FV-NI, Cost
us-gaap_FinancialLiabilitiesFairValueDisclosure
Financial Liabilities Fair Value Disclosure
us-gaap_CashAndCashEquivalentsFairValueDisclosure
Cash and cash equivalents
us-gaap_InvestmentsFairValueDisclosure
Investments, Fair Value Disclosure
Subordinated debt
us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations
Fair Value Measurement Inputs and Valuation Techniques [Table]
Fair Value, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]
Common stock, $1.00 par value per share; 40,000,000 shares authorized; 9,798,948 and 9,828,413 shares issued and outstanding, respectively
Measurement Frequency [Axis]
Adjustments to reconcile net income to net cash provided by operating activities:
Measurement Frequency [Domain]
Common stock, shares authorized (in shares)
Common Stock, Shares Authorized (in shares)
Common stock, shares issued (in shares)
Common stock, par value (in dollars per share)
us-gaap_AssetsSoldUnderAgreementsToRepurchaseInterestRate
Assets Sold under Agreements to Repurchase, Interest Rate
Statistical Measurement [Domain]
Lessee, Lease, Description [Table]
Maximum [Member]
Minimum [Member]
Weighted Average [Member]
Product and Service [Axis]
Product and Service [Domain]
Statistical Measurement [Axis]
Preferred Stock, Liquidation Preference Per Share (in dollars per share)
Preferred Stock, Liquidation Preference Per Share (in dollars per share)
Preferred stock, no par value per share; 5,000,000 shares authorized; 6.5% Series A Non-Cumulative Perpetual Convertible Preferred Stock; 32,500 shares ($1,000 liquidation preference) issued and outstanding at December 31, 2025 and none issued and outstanding at December 31, 2024
Preferred stock, shares issued (in shares)
Interest on deposits and borrowings
Income taxes total
Preferred stock, no par value (in dollars per share)
Property, Plant and Equipment Disclosure [Text Block]
Property, Plant and Equipment [Table Text Block]
Preferred stock, shares authorized (in shares)
Preferred Stock, Shares Authorized (in shares)
Portion at Fair Value Measurement [Member]
Estimate of Fair Value Measurement [Member]
us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)
Measurement Basis [Axis]
Fair Value, Inputs, Level 3 [Member]
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value Hierarchy and NAV [Domain]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Inputs, Level 2 [Member]
us-gaap_PreferredStockRedemptionPricePerShare
Preferred Stock, Redemption Price Per Share (in dollars per share)
Fair Value Hierarchy and NAV [Axis]
Preferred Stock, Dividend Rate
Preferred Stock, Dividend Rate, Percentage
CASH FLOWS FROM OPERATING ACTIVITIES
Cash flows from operating activities
Revenue [Policy Text Block]
Statement [Line Items]
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member]
Surplus
Fair Value, off-Balance-Sheet Risk [Table]
AOCI Attributable to Parent [Member]
us-gaap_AdditionalPaidInCapitalCommonStock
Surplus
STOCKHOLDERS’ EQUITY
Loans, net of allowance
us-gaap_LoansReceivableFairValueDisclosure
Fair Value, by Balance Sheet Grouping [Table]
Fair Value Disclosures [Text Block]
Fair Value, by Balance Sheet Grouping [Table Text Block]
istr_IncreaseDecreaseInShorttermFhlbAdvances
Net increase (decrease) in short-term FHLB advances
Increase (Decrease) in short-term FHLB advances.
us-gaap_Liabilities
Total liabilities
Commitments and contingencies (Note 19)
Counterparty Name [Axis]
Counterparty Name [Domain]
Deferred tax liability
us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Deferred Compensation Liability, Current and Noncurrent, Total
Interest rate swaps - gross liabilities
us-gaap_DerivativeLiabilities
us-gaap_SelfInsuranceReserve
Self Insurance Reserve
Parent Company [Member]
Accrued interest payable
us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued
Subsidiaries [Member]
Accrued taxes and other liabilities
Accounts Payable and Accrued Liabilities
Consolidated Entities [Axis]
Consolidated Entities [Domain]
Accounting Standards Update [Domain]
Accounts payable
Accounting Standards Update [Axis]
Disposal Group Classification [Axis]
Disposal Group Classification [Domain]
Condensed Cash Flow Statement [Table Text Block]
Condensed Balance Sheet [Table Text Block]
Condensed Income Statement [Table Text Block]
Condensed Financial Statements [Table]
Retained Earnings [Member]
Deferred Rent Credit
Additional Paid-in Capital [Member]
Common Stock [Member]
Preferred Stock [Member]
Equity Securities, Held In Correspondent Banks [Member]
Represents held in correspondent banks for equity securities.
Equity Components [Axis]
Bank Owned Life Insurance [Policy Text Block]
Disclosure of accounting policy for bank owned life insurance.
Equity Component [Domain]
Face Value
Transfer from bank premises and equipment to other real estate owned
Represents transfer from bank premises and equipment to other assets.
Stock, Class of Stock [Table]
Other Assets [Member]
Marketable Securities and Mutual Funds [Member]
Asset obtained to generate income or appreciate in value.
Junior subordinated debt
Carrying Value
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust
us-gaap_LineOfCredit
Long-Term Line of Credit
Subordinated debt, net of unamortized issuance costs
Subordinated Debt
us-gaap_DeferredFinanceCostsNet
Debt Issuance Costs, Net
istr_IncreaseDecreaseInDueFromBankSubsidiary
Due from bank subsidiary
The increase (decrease) in due from bank subsidiary.
Dividends received from bank subsidiary
Amount of dividend income from subsidiary.
Management fees to bank subsidiary
Amount of management service fees to subsidiary bank.
Nonaccrual with allowance
Amortized cost of financing receivable on nonaccrual status with allowance for credit loss. Excludes net investment in lease.
Document Annual Report
Computer Equipment [Member]
Statement of Financial Position Location, Balance [Axis]
istr_IncomeLossBeforeEquityInUndistributedIncomeLossOfSubsidiaryIncomeTaxes
Income before income tax benefit and equity in undistributed earnings of bank subsidiary
Amount of income (loss) before equity in undistributed income (loss) of subsidiary and income taxes.
Statement of Financial Position Location, Balance [Domain]
Due from bank subsidiary
The amount due from bank subsidiary as of the balance sheet date.
Investment in trust
The amount of investment in trust as of the balance sheet date.
Entity Incorporation, State or Country Code
Document Transition Report
Document Financial Statement Error Correction [Flag]
us-gaap_OtherShortTermBorrowings
Other Short-Term Borrowings
Entity Interactive Data Current
us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
Securities Sold under Agreements to Repurchase
us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate
2025
Security Exchange Name
Title of 12(b) Security
Statement of Income Location, Balance [Axis]
Deposits
us-gaap_DepositsFairValueDisclosure
Statement of Income Location, Balance [Domain]
Discontinued Operations, Disposed of by Means Other than Sale [Member]
Real Estate, Type of Property [Axis]
Real Estate [Domain]
Transfers from bank premises and equipment
Represents transfers from bank premises and equipment for other real estate owned.
us-gaap_DerivativeCollateralObligationToReturnSecurities
Interest rate swaps, not offset by financial instruments
us-gaap_DerivativeCollateralObligationToReturnCash
Interest rate swaps, not offset, cash collateral
istr_TimeDeposits250000AndAbove
Time Deposits 250,000 and Above
Time deposits 250000 and above.
Interest rate swaps, offset
us-gaap_DerivativeAssetFairValueGrossLiability
istr_DepositsPublicFundsAmount
Deposits Public Funds Amount
Represents deposits public funds amount.
Interest rate swaps - gross assets
us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
Scheduled Maturities of Time Deposits Table [Table Text Block]
Tabular disclosure of maturities of time deposits.
istr_AssetsSoldUnderAgreementsToRepurchaseWeightedAverageInterestRate
Assets Sold under Agreements to Repurchase, Weighted Average Interest Rate
Weighted average interest rate of assets sold under agreements to repurchase.
us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedLiability
Total, offset
Statement [Table]
us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnCash
Total, not offset, cash collateral
us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedGross
Total
us-gaap_DerivativeAssetSecuritiesPurchasedUnderAgreementsToResellSecuritiesBorrowedCollateralObligationToReturnSecurities
Total, not offset by financial instruments
Income Statement [Abstract]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Total other comprehensive income (loss)
Interest rate swaps, offset
us-gaap_DerivativeLiabilityFairValueGrossAsset
Derivative Liability, Subject to Master Netting Arrangement, Asset Offset
Interest rate swaps - gross liabilities
us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral
Securities Sold under Agreements to Repurchase, Fair Value of Collateral
Loan Portfolio [Member]
Represents loan portfolio.
Repurchase agreements
us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseGross
Repurchase agreements
us-gaap_Deposits
Deposits
Total deposits
Repurchase agreements, offset
us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseCollateralRightToReclaimSecurities
Repurchase agreements, not offset by financial instruments
us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseCollateralRightToReclaimCash
Repurchase agreements, not offset, cash collateral
Interest-bearing
Noninterest-bearing
Accounting Standards Update and Change in Accounting Principle [Table]
us-gaap_TimeDeposits
Time Deposits
us-gaap_DerivativeCollateralRightToReclaimCash
Interest rate swaps, not offset, cash collateral
us-gaap_DerivativeCollateralRightToReclaimSecurities
Interest rate swaps, not offset by financial instruments
Deposit Liabilities, Type [Table Text Block]
Other Commitments [Table Text Block]
Other Commitments [Table]
Deposits:
istr_FinancingReceivableImpairedDuringPeriodGross
Financing Receivable, Impaired During Period Gross
Represents the amount of financing receivables impaired during the period.
Commitments to Extend Credit [Member]
us-gaap_StockholdersEquity
Total stockholders’ equity
Balance
Balance
us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Gross Unrealized Losses
Gross Unrealized Gains
us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Interest Rate Swap [Member]
Due after one year through five years, AFS, amortized cost
Due after five years through ten years, AFS, amortized cost
Due after ten years, AFS, amortized cost