Derivative Financial Instruments - Schedule of interest income (expense) recorded on swap transactions (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Interest Rate Swap \| Cash Flow Hedging
Derivative [Line Items]
Interest income (expense) on swap transactions	$ (370)	$ (288)	$ 697	$ (854)

Interest income or expense incurred from sales or purchase of securities and other assets, which the entity does not own, to other parties. Trading liabilities includes the fair value of derivative contracts held for trading that are in loss positions.

No definition available.

Name:	buse_InterestIncomeExpenseTradingLiabilities
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration