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.

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_Covid19LoanModificationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_FullPaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_InterestOnlyDeferralsMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_BlendedPrincipalAndInterestAndInterestOnlyDeferralsMember
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Data Type:	na
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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
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- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_MortgageAndPersonalLoanDeferralsMember
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Data Type:	na
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- Details

Name:	us-gaap_LoanRestructuringModificationAxis=buse_PurchasedHomeEquityLineOfCreditPoolDeferralsMember
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Portfolio Loans - Modified loans with payment deferrals (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) contract	Dec. 31, 2020 USD ($) contract	Dec. 31, 2019 contract
Loans identified as impaired
Number of Contracts \| contract		8	4
COVID-19 loan modifications
Loans identified as impaired
Number of Contracts \| $	34	450
Recorded Investment \| $	$ 128,867	$ 256,414
Commercial
Loans identified as impaired
Number of Contracts \| contract	1	3	2
Commercial \| COVID-19 loan modifications
Loans identified as impaired
Number of Contracts \| contract	32	98
Recorded Investment \| $	$ 128,730	$ 208,624
Commercial \| Full payment deferral
Loans identified as impaired
Number of Contracts \| contract		46
Recorded Investment \| $		$ 37,150
Commercial \| Interest-only deferrals
Loans identified as impaired
Number of Contracts \| contract	32	23
Recorded Investment \| $	$ 128,730	$ 85,270
Commercial \| Blended principal and interest and interest-only deferrals
Loans identified as impaired
Number of Contracts \| contract		29
Recorded Investment \| $		$ 86,204
Consumer \| COVID-19 loan modifications
Loans identified as impaired
Number of Contracts \| contract	2	352
Recorded Investment \| $	$ 137	$ 47,790
Consumer \| Mortgage and personal loan deferrals
Loans identified as impaired
Number of Contracts \| contract	2	351
Recorded Investment \| $	$ 137	$ 47,671
Consumer \| Purchased home equity line of credit pool deferrals
Loans identified as impaired
Number of Contracts \| contract		1
Recorded Investment \| $		$ 119