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Deposits (Narrative) (Details) - USD ($) $ in Thousands | Dec. 31, 2025 | Dec. 31, 2024
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Deposits [Abstract] |  |
Time Deposits, Greater than $250,000 | $ 139,924 | $ 133,691

X
- Definition Time Deposits, Greater than $250,000 + References No definition available. + Details
Name: | isba_TimeDepositsGreaterThan250000
Namespace Prefix: | isba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_DepositsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration