STOCK-BASED COMPENSATION - Schedule of Unamortized Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Share-based Compensation
Total unamortized stock-based compensation	$ 15,309	$ 10,317
SSARs
Share-based Compensation
Total unamortized stock-based compensation	98	0
RSU awards
Share-based Compensation
Total unamortized stock-based compensation	9,236	7,093
PSU awards
Share-based Compensation
Total unamortized stock-based compensation	5,769	3,043
DSU awards
Share-based Compensation
Total unamortized stock-based compensation	$ 206	$ 181
Busey Awards \| 2020 Equity Plan
Share-based Compensation
Weighted average period over which expense is to be recognized on awards issued under Busey's 2020 Equity Plan	1 year 9 months 18 days	2 years 6 months
CrossFirst Replacement Awards
Share-based Compensation
Weighted average period over which expense is to be recognized on awards issued under Busey's 2020 Equity Plan	1 year 2 months 12 days

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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