REGULATORY CAPITAL - Schedule of Regulatory Capital Requirements Applicable to Busey and Busey Bank (Details) $ in Thousands	Jun. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 1,888,100	$ 1,237,301
Minimum Capital Requirement	695,299	394,840
Minimum To Be Well Capitalized	$ 1,004,321	$ 570,325
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1222	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	$ 2,110,850	$ 1,314,301
Minimum Capital Requirement	927,065	526,453
Minimum To Be Well Capitalized	$ 1,236,087	$ 701,938
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1366	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	$ 2,434,172	$ 1,625,943
Minimum Capital Requirement	1,236,087	701,938
Minimum To Be Well Capitalized	$ 1,545,109	$ 877,422
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1575	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	$ 2,110,850	$ 1,314,301
Minimum Capital Requirement	$ 749,585	$ 475,348
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1126	0.1106
Minimum Capital Requirement	0.0400	0.0400
Busey Bank
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,098,016	$ 1,438,296
Minimum Capital Requirement	692,964	393,277
Minimum To Be Well Capitalized	$ 1,000,949	$ 568,067
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1362	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	$ 2,098,016	$ 1,438,296
Minimum Capital Requirement	923,953	524,369
Minimum To Be Well Capitalized	$ 1,231,937	$ 699,159
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1362	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	$ 2,237,760	$ 1,520,938
Minimum Capital Requirement	1,231,937	699,159
Minimum To Be Well Capitalized	$ 1,539,921	$ 873,949
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1453	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	$ 2,098,016	$ 1,438,296
Minimum Capital Requirement	747,971	473,878
Minimum To Be Well Capitalized	$ 934,963	$ 592,347
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1122	0.1214
Minimum Capital Requirement	0.0400	0.0400
Minimum To Be Well Capitalized	0.0500	0.0500