Regulatory Capital (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,046,689	$ 1,036,143
Minimum Capital Requirement, Amount	604,488	590,826
Minimum To Be Well Capitalized, Amount	$ 755,610	$ 738,532
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	13.85%	14.03%
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	$ 921,827	$ 922,395
Minimum Capital Requirement, Amount	453,366	443,120
Minimum To Be Well Capitalized, Amount	$ 604,488	$ 590,826
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	12.20%	12.49%
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	$ 847,827	$ 848,395
Minimum Capital Requirement, Amount	340,025	332,340
Minimum To Be Well Capitalized, Amount	$ 491,147	$ 480,046
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	11.22%	11.49%
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	$ 921,827	$ 922,395
Minimum Capital Requirement, Amount	$ 372,696	$ 373,360
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)	9.89%	9.88%
Minimum Capital Requirement, Ratio (as a percent)	4.00%	4.00%
Busey Bank
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount	$ 1,012,447	$ 1,099,449
Minimum Capital Requirement, Amount	603,538	589,681
Minimum To Be Well Capitalized, Amount	$ 754,422	$ 737,101
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	13.42%	14.92%
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	$ 947,583	$ 1,045,701
Minimum Capital Requirement, Amount	452,653	442,261
Minimum To Be Well Capitalized, Amount	$ 603,538	$ 589,681
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	12.56%	14.19%
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	$ 947,583	$ 1,045,701
Minimum Capital Requirement, Amount	339,490	331,696
Minimum To Be Well Capitalized, Amount	$ 490,374	$ 479,116
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)	12.56%	14.19%
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	$ 947,583	$ 1,045,701
Minimum Capital Requirement, Amount	371,799	373,639
Minimum To Be Well Capitalized, Amount	$ 464,749	$ 467,049
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)	10.19%	11.19%
Minimum Capital Requirement, Ratio (as a percent)	4.00%	4.00%
Minimum To Be Well Capitalized, Ratio (as a percent)	5.00%	5.00%