REGULATORY CAPITAL - Schedule of Regulatory Capital Requirements Applicable to Busey and Busey Bank (Details) $ in Thousands	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 1,871,865	$ 1,237,301
Minimum Capital Requirement	702,221	394,840
Minimum To Be Well Capitalized	$ 1,014,319	$ 570,325
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1200	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	$ 1,879,615	$ 1,314,301
Minimum Capital Requirement	936,295	526,453
Minimum To Be Well Capitalized	$ 1,248,393	$ 701,938
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1205	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	$ 2,321,708	$ 1,625,943
Minimum Capital Requirement	1,248,393	701,938
Minimum To Be Well Capitalized	$ 1,560,491	$ 877,422
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1488	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	$ 1,879,615	$ 1,314,301
Minimum Capital Requirement	$ 580,626	$ 475,348
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1295	0.1106
Minimum Capital Requirement	0.0400	0.0400
Busey Bank
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 1,420,244	$ 1,438,296
Minimum Capital Requirement	394,316	393,277
Minimum To Be Well Capitalized	$ 569,568	$ 568,067
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1621	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	$ 1,420,244	$ 1,438,296
Minimum Capital Requirement	525,755	524,369
Minimum To Be Well Capitalized	$ 701,007	$ 699,159
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1621	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	$ 1,508,341	$ 1,520,938
Minimum Capital Requirement	701,007	699,159
Minimum To Be Well Capitalized	$ 876,259	$ 873,949
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1721	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	$ 1,420,244	$ 1,438,296
Minimum Capital Requirement	470,374	473,878
Minimum To Be Well Capitalized	$ 587,967	$ 592,347
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1208	0.1214
Minimum Capital Requirement	0.0400	0.0400
Minimum To Be Well Capitalized	0.0500	0.0500
CrossFirst Bank
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 652,977
Minimum Capital Requirement	306,018
Minimum To Be Well Capitalized	$ 442,027
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.0960
Minimum Capital Requirement	0.0450
Minimum To Be Well Capitalized	0.0650
Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 652,977
Minimum Capital Requirement	408,025
Minimum To Be Well Capitalized	$ 544,033
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.0960
Minimum Capital Requirement	0.0600
Minimum To Be Well Capitalized	0.0800
Total Capital to Risk Weighted Assets, Amount
Actual	$ 698,395
Minimum Capital Requirement	544,033
Minimum To Be Well Capitalized	$ 680,041
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1027
Minimum Capital Requirement	0.0800
Minimum To Be Well Capitalized	0.1000
Leverage Ratio of Tier 1 Capital to Average Assets, Amount
Actual	$ 652,977
Minimum Capital Requirement	297,548
Minimum To Be Well Capitalized	$ 371,936
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.0878
Minimum Capital Requirement	0.0400
Minimum To Be Well Capitalized	0.0500