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SIGNIFICANT ACCOUNTING POLICIES - Trust Assets (Details) - USD ($) $ in Billions | Dec. 31, 2023 | Dec. 31, 2022
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Accounting Policies [Abstract] |  |
Assets under care | $ 12.1 | $ 11.1

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- Definition Assets under care held for customers, that are not included in the Company's consolidated financial statements. + References No definition available. + Details
Name: | buse_CustomerAssetsHeldInTrust
Namespace Prefix: | buse_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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