Financing Receivable, Modified, Weighted Average Extended Maturity from Modification

No definition available.

Name:	isba_FinancingReceivableModifiedWeightedAverageExtendedMaturityFromModification
Namespace Prefix:	isba_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Modified, Weighted Average Payment Deferral from Modification

+ References

No definition available.

+ Details

Name:	isba_FinancingReceivableModifiedWeightedAveragePaymentDeferralFromModification
Namespace Prefix:	isba_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-34

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Percentage of decrease in weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateDecreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_CommercialAndIndustrialSecuredPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_CommercialRealEstateOwnerOccupiedPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_CommercialRealEstateNonOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_AgriculturalMortgagePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_InterestRateBelowMarketReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_AgriculturalOtherPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_ResidentialRealEstateSeniorLienPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=isba_ConsumerSecuredIndirectPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and ACL (Summary of Loan Modification Effects) (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023
Commercial and Industrial, Secured, Portfolio Segment \| Payment Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Payment Deferral		4 months
Commercial and Industrial, Secured, Portfolio Segment \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term		3 years
Commercial Real Estate, Owner Occupied, Portfolio Segment \| Payment Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Payment Deferral		7 months
Commercial Real Estate, Non-owner Occupied \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term			3 years
Agricultural Mortgage, Portfolio Segment \| Payment Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Payment Deferral		5 months
Agricultural Mortgage, Portfolio Segment \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term		6 months	1 year 29 days
Agricultural Mortgage, Portfolio Segment \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification			4.50%
Agricultural Other Portfolio Segment [Member] \| Payment Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Payment Deferral		4 months
Agricultural Other Portfolio Segment [Member] \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term		3 months 29 days	1 year
Agricultural Other Portfolio Segment [Member] \| Interest Rate Below Market Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification	0.50%	0.50%
Residential Real Estate, Senior Lien, Portfolio Segment \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term			2 years 7 months 6 days
Consumer, Secured, Indirect, Portfolio Segment \| Extended Maturity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modification Weighted Average Extension Term		1 year 3 months 29 days