XML 68 R55.htm IDEA: XBRL DOCUMENT
v3.25.4

Loans and ACL - Summary of Loan Modifications by Type (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024
Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 18 | $ 132
Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | 1,474 | 3,905
Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | 5,403 | 1,645
Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | 975 | 1,107
Commercial and industrial: Secured | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 18 | $ 0
% of Total Class of Financial Receivable | 0.01% | 0.00%
Commercial and industrial: Secured | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 1,782
% of Total Class of Financial Receivable | 0.00% | 0.80%
Commercial and industrial: Secured | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 3,144 | $ 10
% of Total Class of Financial Receivable | 1.66% | 0.00%
Commercial and industrial: Secured | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 975 | $ 0
% of Total Class of Financial Receivable | 0.52% | 0.00%
Commercial mortgage owner occupied | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 0
% of Total Class of Financial Receivable | 0.00% | 0.00%
Commercial mortgage owner occupied | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 818
% of Total Class of Financial Receivable | 0.00% | 0.46%
Commercial mortgage owner occupied | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 1,483 | $ 1,353
% of Total Class of Financial Receivable | 0.65% | 0.76%
Commercial mortgage owner occupied | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 0
% of Total Class of Financial Receivable | 0.00% | 0.00%
Agricultural mortgage | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 0
% of Total Class of Financial Receivable | 0.00% | 0.00%
Agricultural mortgage | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 1,389 | $ 1,305
% of Total Class of Financial Receivable | 1.99% | 1.93%
Agricultural mortgage | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 281
% of Total Class of Financial Receivable | 0.00% | 0.42%
Agricultural mortgage | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 0
% of Total Class of Financial Receivable | 0.00% | 0.00%
Agricultural other | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 132
% of Total Class of Financial Receivable | 0.00% | 0.41%
Agricultural other | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 0
% of Total Class of Financial Receivable | 0.00% | 0.00%
Agricultural other | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 776 | $ 0
% of Total Class of Financial Receivable | 2.40% | 0.00%
Agricultural other | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 | $ 1,107
% of Total Class of Financial Receivable | 0.00% | 3.44%
Residential real estate: Senior Lien | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 |
% of Total Class of Financial Receivable | 0.00% |
Residential real estate: Senior Lien | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 85 |
% of Total Class of Financial Receivable | 0.02% |
Residential real estate: Senior Lien | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 |
% of Total Class of Financial Receivable | 0.00% |
Residential real estate: Senior Lien | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis | $ 0 |
% of Total Class of Financial Receivable | 0.00% |
Consumer: Secured - indirect | Interest Rate Reduction |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis |  | $ 0
% of Total Class of Financial Receivable |  | 0.00%
Consumer: Secured - indirect | Other-Than-Insignificant Payment Delay |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis |  | $ 0
% of Total Class of Financial Receivable |  | 0.00%
Consumer: Secured - indirect | Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis |  | $ 1
% of Total Class of Financial Receivable |  | 0.00%
Consumer: Secured - indirect | Other-Than-Insignificant Payment Delay and Term Extension |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Amortized Cost Basis |  | $ 0
% of Total Class of Financial Receivable |  | 0.00%

X
- Definition Percentage of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables. + 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 Reference 2: 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_FinancingReceivableModificationToTotalFinancingReceivablesPercent
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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://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 2: 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 3: 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 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

X
- Definition Amortized cost of financing receivable modified during period 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 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/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_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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

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

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=isba_ExtendedMaturityAndPaymentDeferralMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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

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

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