Loans (Details 5)	9 Months Ended
Sep. 30, 2013 item	Dec. 31, 2012
Loans
The number of components in the general portion of the Company's allowance	2
Number of quarters whose historical average is used to calculate the historical loss ratio	20
Grade 8
Loans
Number of quarters in more current measure of historical losses in adversely graded loans	12
Number of quarters in less current measure of historical losses in adversely graded loans	20
Minimum additional amount for loans (as a percent)	1.00%	1.00%
Grade 9
Loans
Period of charge-off percentage based on which additional allocation is determined	1 year
Minimum additional reserve (as a percent)	3.00%	3.00%

The number of components in the general portion of the Company's allowance determination.

No definition available.

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

- Definition

Represents the number of quarters in less current measure of historical losses in adversely graded loans. This measure is compared to another to determine if the entity should make an additional allocation for loan losses.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of quarters in more current measure of historical losses in adversely graded loans. If the more current loss trend exceeds the less current measure, an additional allocation is made for loan losses.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of quarters whose historical average is used to calculate the historical loss ratio.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of minimum additional amount for loans based upon review of difference between rolling quarter historical averages by region.

+ References

No definition available.

+ Details

Name:	buse_PercentageOfMinimumAdditionalAmountForLoansBasedOnDifferenceBetweenHistoricalLossAveragesByRegion
Namespace Prefix:	buse_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of minimum additional reserve which is an estimate of the additional loss inherent in loan grades based upon a review of overall historical charge-offs.

+ References

No definition available.

+ Details

Name:	buse_PercentageOfMinimumAdditionalReserveBasedOnOverallHistoricalChargeOff
Namespace Prefix:	buse_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the period of charge-off percentage based on which additional allocation is determined.

+ References

No definition available.

+ Details

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

- Details

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