Reportable Segments and Related Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Reportable Segments and Related Information
Number of reportable segments | item			3
Goodwill	$ 25,510		$ 25,510		$ 20,686
Total Assets	3,863,565		3,863,565		3,665,607
Interest Income	29,730	$ 27,511	86,903	$ 80,418
Interest Expense	1,535	1,600	4,687	4,929
Other Income	15,889	14,204	48,477	44,202
Noninterest Expense	27,950	26,298	86,942	79,739
Income before income taxes	16,034	13,817	43,151	37,952
Net Income:	10,626	9,109	28,323	25,181
Operating segments
Reportable Segments and Related Information
Goodwill	25,510		25,510		20,686
Total Assets	3,863,565		3,863,565		3,665,607
Operating segments | Busey Bank
Reportable Segments and Related Information
Goodwill	4,824		4,824
Total Assets	3,790,377		3,790,377		3,589,419
Interest Income	29,660	27,430	86,688	80,184
Interest Expense	1,240	1,312	3,818	4,072
Other Income	8,227	7,595	25,579	23,748
Noninterest Expense	21,961	21,162	68,598	63,213
Income before income taxes	14,586	12,552	39,251	34,647
Net Income:	9,438	8,195	25,531	22,910
Operating segments | FirsTech
Reportable Segments and Related Information
Goodwill	8,992		8,992		8,992
Total Assets	29,900		29,900		28,540
Interest Income	14	14	40	39
Other Income	2,973	2,412	8,518	7,208
Noninterest Expense	2,186	1,876	6,337	5,614
Income before income taxes	801	550	2,221	1,633
Net Income:	479	322	1,329	957
Operating segments | Busey Wealth Management
Reportable Segments and Related Information
Goodwill	11,694		11,694		11,694
Total Assets	32,375		32,375		31,196
Interest Income	67	74	206	214
Other Income	5,053	4,640	15,320	14,291
Noninterest Expense	3,127	2,702	9,535	8,412
Income before income taxes	1,993	2,012	5,991	6,093
Net Income:	1,189	1,176	3,577	3,579
Other
Reportable Segments and Related Information
Total Assets	10,913		10,913		$ 16,452
Interest Income, Net	(11)	(7)	(31)	(19)
Interest Expense	295	288	869	857
Other Income	(364)	(443)	(940)	(1,045)
Noninterest Expense	676	558	2,472	2,500
Income before income taxes	(1,346)	(1,297)	(4,312)	(4,421)
Net Income:	$ (480)	$ (584)	$ (2,114)	$ (2,265)