OREO (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Foreclosed Real Estate
Other real estate owned (OREO)	$ 376	$ 376	$ 3,057
OREO
Other Real Estate, Beginning Balance	376	1,283
Additions, transfers from loans	4,872	4,025
Additions, fair value from acquisition	149
Sales of OREO	(2,277)	(4,914)
Capitalized improvements	2
Cash payments collected	(3)
Valuation allowance for OREO	(62)	(18)
Other Real Estate, Ending Balance	3,057	376
Commercial Real Estate Loans
Foreclosed Real Estate
Other real estate owned (OREO)	200	200	2,700
OREO
Other Real Estate, Beginning Balance	200
Other Real Estate, Ending Balance	2,700	200
Residential real estate
Foreclosed Real Estate
Other real estate owned (OREO)	200	200	400
Residential real estate in the process of foreclosure			$ 2,200
OREO
Other Real Estate, Beginning Balance	200
Other Real Estate, Ending Balance	$ 400	$ 200

Value transferred from commercial and mortgage loans to real estate owned (REO) in noncash transactions.

No definition available.

Name:	buse_CommercialAndMortgageTransferToOtherRealEstate
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents capitalized improvements.

+ References

No definition available.

+ Details

Name:	buse_ForeclosedRealEstateCapitalizedImprovements
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Additions of other real estate, at fair value, resulting from an acquisition. This includes prior real estate assets taken in settlement of troubled loans through surrender or foreclosure.

+ References

No definition available.

+ Details

Name:	buse_OtherRealEstateAdditionsFairValueFromAcquisition
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash payments collected from other real estate.

+ References

No definition available.

+ Details

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

- Definition

Represents the value of real estate loans in the process of foreclosure at period end.

+ References

No definition available.

+ Details

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

- Definition

Represents assets taken in foreclosure.

+ References

No definition available.

+ Details

Name:	buse_SalesOfOreo
Namespace Prefix:	buse_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5162-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4437-111522

+ Details

Name:	us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total Increase or Decrease in the real estate owned valuation allowance for period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_RealEstateOwnedValuationAllowancePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_CollateralAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CollateralAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: