Capital - (Details) - USD ($) $ in Thousands		9 Months Ended
	Oct. 12, 2017	Sep. 30, 2017	Jan. 01, 2019	Jan. 01, 2017	Jul. 31, 2013
Total Capital (to Risk Weighted Assets), Amount
Actual		$ 790,889
Minimum Capital Requirement with Capital Buffer		508,861
Minimum To Be Well Capitalized		$ 550,120
Total Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		14.38%
Minimum Capital Requirement with Capital Buffer (as a percent)		9.25%
Minimum To Be Well Capitalized (as a percent)		10.00%
Tier 1 Capital (to Risk Weighted Assets), Amount
Actual		$ 674,354
Minimum Capital Requirement with Capital Buffer		398,837
Minimum To Be Well Capitalized		$ 440,096
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		12.26%
Minimum Capital Requirement with Capital Buffer (as a percent)		7.25%
Minimum To Be Well Capitalized (as a percent)		8.00%
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Amount
Actual		$ 600,886
Minimum Capital Requirement with Capital Buffer		316,319
Minimum To Be Well Capitalized		$ 357,578
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Ratio
Actual (as a percent)		10.92%
Minimum Capital Requirement with Capital Buffer (as a percent)		5.75%
Minimum To Be Well Capitalized (as a percent)		6.50%
Tier 1 Capital (to Average Assets), Amount
Actual		$ 674,354
Minimum Capital Requirement with Capital Buffer		$ 265,020
Tier 1 Capital (to Average Assets), Ratio
Actual (as a percent)		10.18%
Minimum Capital Requirement with Capital Buffer (as a percent)		4.00%
Dodd-Frank Act ("Basel III Rules")
Regulatory Capital
Maximum consolidated assets of bank holding companies					$ 1,000,000
Maximum consolidated assets size of bank holding companies potentially unaffected by certain Tier 1 capital restrictions		$ 15,000,000
Common Equity Tier 1 capital conservation buffer of risk weighted assets		2.50%
Tier 1 Capital (to Average Assets), Ratio
Increase in minimum capital requirement ratios				1.25%
Capital buffer requirement period		3 years
Forecast
Total Capital (to Risk Weighted Assets), Ratio
Minimum Capital Requirement with Capital Buffer (as a percent)			10.50%
Tier 1 Capital (to Risk Weighted Assets), Ratio
Minimum Capital Requirement with Capital Buffer (as a percent)			8.50%
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Ratio
Minimum Capital Requirement with Capital Buffer (as a percent)			7.00%
Busey Bank
Regulatory Capital
Distribution received through chartered amendment	$ 40,000
Total Capital (to Risk Weighted Assets), Amount
Actual		$ 601,898
Minimum Capital Requirement with Capital Buffer		392,377
Minimum To Be Well Capitalized		$ 424,191
Total Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		14.19%
Minimum Capital Requirement with Capital Buffer (as a percent)		9.25%
Minimum To Be Well Capitalized (as a percent)		10.00%
Tier 1 Capital (to Risk Weighted Assets), Amount
Actual		$ 552,496
Minimum Capital Requirement with Capital Buffer		307,539
Minimum To Be Well Capitalized		$ 339,353
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		13.02%
Minimum Capital Requirement with Capital Buffer (as a percent)		7.25%
Minimum To Be Well Capitalized (as a percent)		8.00%
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Amount
Actual		$ 552,496
Minimum Capital Requirement with Capital Buffer		243,910
Minimum To Be Well Capitalized		$ 275,724
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Ratio
Actual (as a percent)		13.02%
Minimum Capital Requirement with Capital Buffer (as a percent)		5.75%
Minimum To Be Well Capitalized (as a percent)		6.50%
Tier 1 Capital (to Average Assets), Amount
Actual		$ 552,496
Minimum Capital Requirement with Capital Buffer		208,351
Minimum To Be Well Capitalized		$ 260,438
Tier 1 Capital (to Average Assets), Ratio
Actual (as a percent)		10.61%
Minimum Capital Requirement with Capital Buffer (as a percent)		4.00%
Minimum To Be Well Capitalized (as a percent)		5.00%
First Community Financial Bank
Total Capital (to Risk Weighted Assets), Amount
Actual		$ 125,857
Minimum Capital Requirement with Capital Buffer		112,542
Minimum To Be Well Capitalized		$ 121,667
Total Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		10.34%
Minimum Capital Requirement with Capital Buffer (as a percent)		9.25%
Minimum To Be Well Capitalized (as a percent)		10.00%
Tier 1 Capital (to Risk Weighted Assets), Amount
Actual		$ 124,224
Minimum Capital Requirement with Capital Buffer		88,209
Minimum To Be Well Capitalized		$ 97,334
Tier 1 Capital (to Risk Weighted Assets), Ratio
Actual (as a percent)		10.21%
Minimum Capital Requirement with Capital Buffer (as a percent)		7.25%
Minimum To Be Well Capitalized (as a percent)		8.00%
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Amount
Actual		$ 124,224
Minimum Capital Requirement with Capital Buffer		69,959
Minimum To Be Well Capitalized		$ 79,084
Equity Tier 1 Capital (to Risk Weighted Assets) Common, Ratio
Actual (as a percent)		10.21%
Minimum Capital Requirement with Capital Buffer (as a percent)		5.75%
Minimum To Be Well Capitalized (as a percent)		6.50%
Tier 1 Capital (to Average Assets), Amount
Actual		$ 124,224
Minimum Capital Requirement with Capital Buffer		55,590
Minimum To Be Well Capitalized		$ 69,487
Tier 1 Capital (to Average Assets), Ratio
Actual (as a percent)		8.94%
Minimum Capital Requirement with Capital Buffer (as a percent)		4.00%
Minimum To Be Well Capitalized (as a percent)		5.00%