Reportable Segments and Related Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Reportable Segments and Related Information
Number of reportable segments | item			3
Reportable Segments and Related Information
Goodwill	$ 25,510		$ 25,510		$ 20,686
Total Assets	3,885,274		3,885,274		3,665,607
Interest Income	28,910	$ 26,656	57,173	$ 52,907
Interest Expense	1,559	1,635	3,152	3,329
Other Income	16,623	15,012	32,588	29,998
Noninterest Expense	28,445	26,823	58,992	53,441
Income before income taxes	15,529	12,210	27,117	24,135
Net Income:	9,936	8,185	17,697	16,072
Operating segments
Reportable Segments and Related Information
Goodwill	25,510		25,510		20,686
Total Assets	3,885,274		3,885,274		3,665,607
Operating segments | Busey Bank
Reportable Segments and Related Information
Goodwill	4,824		4,824
Total Assets	3,806,655		3,806,655		3,589,419
Interest Income	28,839	26,573	57,028	52,754
Interest Expense	1,268	1,350	2,578	2,760
Other Income	8,383	7,926	17,352	16,153
Noninterest Expense	22,337	21,007	46,637	42,051
Income before income taxes	13,617	11,141	24,665	22,095
Net Income:	8,815	7,436	16,093	14,715
Operating segments | FirsTech
Reportable Segments and Related Information
Goodwill	8,992		8,992		8,992
Total Assets	29,519		29,519		28,540
Interest Income	13	13	26	25
Other Income	3,013	2,409	5,545	4,796
Noninterest Expense	2,205	1,866	4,151	3,738
Income before income taxes	821	555	1,420	1,083
Net Income:	492	326	850	635
Operating segments | Busey Wealth Management
Reportable Segments and Related Information
Goodwill	11,694		11,694		11,694
Total Assets	32,164		32,164		31,196
Interest Income	68	76	139	140
Other Income	5,588	5,110	10,267	9,651
Noninterest Expense	3,273	2,807	6,408	5,710
Income before income taxes	2,383	2,379	3,998	4,081
Net Income:	1,425	1,401	2,388	2,403
Other
Reportable Segments and Related Information
Total Assets	16,936		16,936		$ 16,452
Interest Income, Net	(10)	(6)	(20)	(12)
Interest Expense	291	285	574	569
Other Income	(361)	(433)	(576)	(602)
Noninterest Expense	630	1,143	1,796	1,942
Income before income taxes	(1,292)	(1,865)	(2,966)	(3,124)
Net Income:	$ (796)	$ (978)	$ (1,634)	$ (1,681)