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

Assets under care held for customers, that are not included in the Company's consolidated financial statements.

No definition available.

Name:	buse_CustomerAssetsHeldInTrust
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant