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Significant Accounting Policies - Subsequent Events (Details) - Subsequent event	Jul. 27, 2021 Center
Subsequent Event [Line Items]
Number of banking centers consolidated	15
GSB
Subsequent Event [Line Items]
Number of banking centers consolidated	2

X

- Definition

Represents the number of banking centers consolidated.

+ References

No definition available.

+ Details

Name:	buse_NumberOfBankingCentersConsolidated
Namespace Prefix:	buse_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidatedEntitiesAxis=buse_GsbBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: