Borrowings - Maturity period (Details)	3 Months Ended
Mar. 31, 2020
Maturity period
Maximum maturity period of short-term debt	1 year

Represents the maximum maturity period of short-term debt.

No definition available.

Name:	buse_ShortTermDebtMaturityPeriodMaximum
Namespace Prefix:	buse_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration