v3.25.2

Borrowed Funds (Pledged financial instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Disclosure [Abstract]
Pledged Assets	$ 531,425	$ 548,987
Short-term Debt [Line Items]
Pledged Financial Instruments, Available for Sale Securities, without Single Maturity Date	58,119	67,539
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	405,027	395,286
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	58,119	67,539
Deposit Liabilities, Collateral Issued, Financial Instruments	68,279	86,162
US Treasury Securities
Short-term Debt [Line Items]
Pledged Financial Instruments, Available for Sale Securities, without Single Maturity Date	48,486	57,271
Mortgage-Backed Securities, Other
Short-term Debt [Line Items]
Pledged Financial Instruments, Available for Sale Securities, without Single Maturity Date	7,508	7,979
Collateralized Mortgage Obligations [Member]
Short-term Debt [Line Items]
Pledged Financial Instruments, Available for Sale Securities, without Single Maturity Date	$ 2,125	$ 2,289

Pledged Financial Instruments, Available for Sale Securities, without Single Maturity Date

+ References

No definition available.

+ Details

Name:	isba_PledgedFinancialInstrumentsAvailableforSaleSecuritieswithoutSingleMaturityDate
Namespace Prefix:	isba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Pledged Financial Instruments, Not Separately Reported, Securities And Loans Receivable Pledged As Collateral

+ References

No definition available.

+ Details

Name:	isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral
Namespace Prefix:	isba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_DebtDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478353/942-405-50-1

+ Details

Name:	us-gaap_DepositLiabilitiesCollateralIssuedFinancialInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478878/942-470-45-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477734/942-470-50-3

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-20

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

+ Details

Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShortTermDebtLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_MortgageBackedSecuritiesOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

ISABELLA BANK CORP 10-Q