EMPLOYEE BENEFIT PLANS - Narrative (Details)	12 Months Ended
Dec. 31, 2025
Employee Benefit Plans
Employer matching contribution, percent of match	100.00%
Employer matching contribution, percent of employees' gross pay	3.00%
Employer matching contribution, percent of next match	50.00%
Employer next matching contribution, percent of employees' gross pay	2.00%
Vesting period	5 years

Defined Contribution Plan, Second Employer Matching Contribution, Percent of Employees' Gross Pay

No definition available.

Name:	buse_DefinedContributionPlanSecondEmployerMatchingContributionPercentOfEmployeesGrossPay
Namespace Prefix:	buse_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Defined Contribution Plan, Second Employer Matching Contribution, Percent of Second Match

No definition available.

Name:	buse_DefinedContributionPlanSecondEmployerMatchingContributionPercentOfSecondMatch
Namespace Prefix:	buse_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Represents the period during which the rights of the participants vest under the defined contribution plans.

No definition available.

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

Employee Benefit Plans

No definition available.

Name:	buse_EmployeeBenefitPlansDisclosureAbstract
Namespace Prefix:	buse_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage employer matches of the employee's percentage contribution matched.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration