STOCK-BASED COMPENSATION - Schedule of Changes in the Company's RSU, PSU, and DSU Awards (Details)	6 Months Ended
	Jun. 30, 2025 $ / shares shares
Shares
Modifications based on CrossFirst acquisition (in shares) | shares	(181,828)
Weighted- Average Grant Date Fair Value
Modifications based on CrossFirst acquisition (in dollars per share) | $ / shares	$ 20.43
RSU Awards
Shares
Non-vested at beginning of period (in shares) | shares	1,066,772
Conversion of Busey ROATCE PSUs to RSUs (in shares) | shares	157,094
Granted (in shares) | shares	352,763
Dividend equivalents earned (in shares) | shares	32,855
Vested (in shares) | shares	(98,014)
Forfeited (in shares) | shares	(107,568)
Non-vested at end of period (in shares) | shares	1,744,950
Weighted- Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share) | $ / shares	$ 21.80
Conversion of Busey ROATCE PSUs to RSUs (in dollars per share) | $ / shares	23.99
Granted (in dollars per share) | $ / shares	22.16
Dividend equivalents earned (in dollars per share) | $ / shares	21.88
Vested (in dollars per share) | $ / shares	23.76
Forfeited (in dollars per share) | $ / shares	21.99
Non-vested at end of period (in dollars per share) | $ / shares	$ 22.38
RSU Awards | CrossFirst
Shares
Replacement of CrossFirst RSUs and PSUs (in shares) | shares	341,048
Weighted- Average Grant Date Fair Value
Replacement of CrossFirst RSUs and PSUs (in dollars per share) | $ / shares	$ 23.99
PSU Awards
Shares
Non-vested at beginning of period (in shares) | shares	372,042
Granted (in shares) | shares	407,723
Vested (in shares) | shares	(155)
Forfeited (in shares) | shares	(32,620)
Non-vested at end of period (in shares) | shares	565,162
Weighted- Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share) | $ / shares	$ 21.15
Granted (in dollars per share) | $ / shares	20.99
Vested (in dollars per share) | $ / shares	22.06
Forfeited (in dollars per share) | $ / shares	21.01
Non-vested at end of period (in dollars per share) | $ / shares	$ 21.28
DSU Awards
Shares
Non-vested at beginning of period (in shares) | shares	36,893
Granted (in shares) | shares	39,846
Dividend equivalents earned (in shares) | shares	4,474
Vested (in shares) | shares	(40,885)
Non-vested at end of period (in shares) | shares	40,328
Vested and outstanding at end of period (in shares) | shares	142,922
Weighted- Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share) | $ / shares	$ 23.40
Granted (in dollars per share) | $ / shares	22.16
Dividend equivalents earned (in dollars per share) | $ / shares	22.51
Vested (in dollars per share) | $ / shares	23.33
Non-vested at end of period (in dollars per share) | $ / shares	22.14
Vested and outstanding at end of period (in dollars per share) | $ / shares	$ 23.01