Regulatory Capital (Details) $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,265,926	$ 1,245,997
Minimum Capital Requirement, Amount	582,526	585,015
Minimum To Be Well Capitalized, Amount	$ 728,157	$ 731,269
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	17.39	17.04
Minimum Capital Requirement, Ratio (as a percent)	8.00	8.00
Minimum To Be Well Capitalized, Ratio (as a percent)	10.00	10.00
Tier 1 Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,007,986	$ 983,033
Minimum Capital Requirement, Amount	436,894	438,761
Minimum To Be Well Capitalized, Amount	$ 582,526	$ 585,015
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	13.84	13.44
Minimum Capital Requirement, Ratio (as a percent)	6.00	6.00
Minimum To Be Well Capitalized, Ratio (as a percent)	8.00	8.00
Common Equity Tier 1 Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 933,986	$ 909,033
Minimum Capital Requirement, Amount	327,671	329,071
Minimum To Be Well Capitalized, Amount	$ 473,302	$ 475,325
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	12.83%	12.43%
Minimum Capital Requirement, Ratio (as a percent)	4.50%	4.50%
Minimum To Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 Capital (to Average Assets), Amount
Actual, Amount	$ 1,007,986	$ 983,033
Minimum Capital Requirement, Amount	$ 409,360	$ 401,717
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)	9.85	9.79
Minimum Capital Requirement, Ratio (as a percent)	4.00	4.00
Busey Bank
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,167,199	$ 1,131,875
Minimum Capital Requirement, Amount	581,457	584,082
Minimum To Be Well Capitalized, Amount	$ 726,821	$ 730,103
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	16.06	15.50
Minimum Capital Requirement, Ratio (as a percent)	8.00	8.00
Minimum To Be Well Capitalized, Ratio (as a percent)	10.00	10.00
Tier 1 Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,094,260	$ 1,053,910
Minimum Capital Requirement, Amount	436,093	438,062
Minimum To Be Well Capitalized, Amount	$ 581,457	$ 584,082
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	15.06	14.44
Minimum Capital Requirement, Ratio (as a percent)	6.00	6.00
Minimum To Be Well Capitalized, Ratio (as a percent)	8.00	8.00
Common Equity Tier 1 Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,094,260	$ 1,053,910
Minimum Capital Requirement, Amount	327,070	328,546
Minimum To Be Well Capitalized, Amount	$ 472,434	$ 474,567
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	15.06%	14.44%
Minimum Capital Requirement, Ratio (as a percent)	4.50%	4.50%
Minimum To Be Well Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 Capital (to Average Assets), Amount
Actual, Amount	$ 1,094,260	$ 1,053,910
Minimum Capital Requirement, Amount	408,522	400,581
Minimum To Be Well Capitalized, Amount	$ 510,652	$ 500,727
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)	10.71	10.52
Minimum Capital Requirement, Ratio (as a percent)	4.00	4.00
Minimum To Be Well Capitalized, Ratio (as a percent)	5.00	5.00