Regulatory Capital (Details) - USD ($) $ in Thousands	Oct. 12, 2018	Dec. 31, 2019	Dec. 31, 2018
Regulatory Capital
Distribution received through chartered amendment	$ 40,000
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount		$ 1,036,143	$ 894,572
Minimum Capital Requirement, Amount		590,826	482,638
Minimum To Be Well Capitalized, Amount		$ 738,532	$ 603,297
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		14.03%	14.83%
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		$ 922,395	$ 783,924
Minimum Capital Requirement, Amount		443,120	361,978
Minimum To Be Well Capitalized, Amount		$ 590,826	$ 482,638
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		12.49%	12.99%
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		$ 848,395	$ 709,924
Minimum Capital Requirement, Amount		332,340	271,484
Minimum To Be Well Capitalized, Amount		$ 480,046	$ 392,143
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		11.49%	11.77%
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		$ 922,395	$ 783,924
Minimum Capital Requirement, Amount		$ 373,360	$ 302,704
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)		9.88%	10.36%
Minimum Capital Requirement, Ratio (as a percent)		4.00%	4.00%
Busey Bank
Total Capital (to Risk Weighted Assets), Amount
Actual, Amount		$ 1,099,449	$ 854,351
Minimum Capital Requirement, Amount		589,681	481,701
Minimum To Be Well Capitalized, Amount		$ 737,101	$ 602,126
Total Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		14.92%	14.19%
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		$ 1,045,701	$ 803,703
Minimum Capital Requirement, Amount		442,261	361,276
Minimum To Be Well Capitalized, Amount		$ 589,681	$ 481,701
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		14.19%	13.35%
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		$ 1,045,701	$ 803,703
Minimum Capital Requirement, Amount		331,696	270,957
Minimum To Be Well Capitalized, Amount		$ 479,116	$ 391,382
Common Equity Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual, Ratio (as a percent)		14.19%	13.35%
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		$ 1,045,701	$ 803,703
Minimum Capital Requirement, Amount		373,639	302,232
Minimum To Be Well Capitalized, Amount		$ 467,049	$ 377,789
Tier 1 Capital (to Average Assets), Ratio
Actual, Ratio (as a percent)		11.19%	10.64%
Minimum Capital Requirement, Ratio (as a percent)		4.00%	4.00%
Minimum To Be Well Capitalized, Ratio (as a percent)		5.00%	5.00%