REGULATORY CAPITAL - Schedule of Regulatory Capital Requirements Applicable to Busey and Busey Bank (Details) $ in Thousands	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 1,920,388	$ 1,237,301
Minimum Capital Requirement	694,987	394,840
Minimum To Be Well Capitalized	$ 1,003,870	$ 570,325
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1243	0.1410
Minimum Capital Requirement	0.0450	0.0450
Minimum To Be Well Capitalized	0.0650	0.0650
Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,143,138	$ 1,314,301
Minimum Capital Requirement	926,650	526,453
Minimum To Be Well Capitalized	$ 1,235,533	$ 701,938
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1388	0.1498
Minimum Capital Requirement	0.0600	0.0600
Minimum To Be Well Capitalized	0.0800	0.0800
Total Capital to Risk Weighted Assets, Amount
Actual	$ 2,459,847	$ 1,625,943
Minimum Capital Requirement	1,235,533	701,938
Minimum To Be Well Capitalized	$ 1,544,416	$ 877,422
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1593	0.1853
Minimum Capital Requirement	0.0800	0.0800
Minimum To Be Well Capitalized	0.1000	0.1000
Leverage Ratio of Tier 1 Capital to Average Assets, Amount
Actual	$ 2,143,138	$ 1,314,301
Minimum Capital Requirement	$ 718,334	$ 475,348
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1193	0.1106
Minimum Capital Requirement	0.0400	0.0400
Busey Bank
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,150,048	$ 1,438,296
Minimum Capital Requirement	692,654	393,277
Minimum To Be Well Capitalized	$ 1,000,500	$ 568,067
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1397	0.1646
Minimum Capital Requirement	0.0450	0.0450
Minimum To Be Well Capitalized	0.0650	0.0650
Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,150,048	$ 1,438,296
Minimum Capital Requirement	923,539	524,369
Minimum To Be Well Capitalized	$ 1,231,385	$ 699,159
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1397	0.1646
Minimum Capital Requirement	0.0600	0.0600
Minimum To Be Well Capitalized	0.0800	0.0800
Total Capital to Risk Weighted Assets, Amount
Actual	$ 2,287,179	$ 1,520,938
Minimum Capital Requirement	1,231,385	699,159
Minimum To Be Well Capitalized	$ 1,539,231	$ 873,949
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1486	0.1740
Minimum Capital Requirement	0.0800	0.0800
Minimum To Be Well Capitalized	0.1000	0.1000
Leverage Ratio of Tier 1 Capital to Average Assets, Amount
Actual	$ 2,150,048	$ 1,438,296
Minimum Capital Requirement	716,476	473,878
Minimum To Be Well Capitalized	$ 895,596	$ 592,347
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1200	0.1214
Minimum Capital Requirement	0.0400	0.0400
Minimum To Be Well Capitalized	0.0500	0.0500