STOCK-BASED COMPENSATION - Schedule of changes in the Company's RSU, PSU, and DSU awards (Details)	12 Months Ended
	Dec. 31, 2025 $ / shares shares
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	387,882
Dividend equivalents earned (in shares) | shares	63,864
Vested (in shares) | shares	(547,788)
Forfeited (in shares) | shares	(148,335)
Non-vested at end of period (in shares) | shares	1,320,537
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	22.28
Dividend equivalents earned (in dollars per share) | $ / shares	22.32
Vested (in dollars per share) | $ / shares	20.77
Forfeited (in dollars per share) | $ / shares	22.48
Non-vested at end of period (in dollars per share) | $ / shares	$ 23.14
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
Modifications based on CrossFirst acquisition (in shares) | shares	(181,828)
Granted (in shares) | shares	407,723
Dividend equivalents earned (in shares) | shares	198
Vested (in shares) | shares	(21,792)
Forfeited (in shares) | shares	(50,842)
Non-vested at end of period (in shares) | shares	525,501
Vested and outstanding at end of period (in shares) | shares	13,455
Weighted- Average Grant Date Fair Value
Non-vested at beginning of period (in dollars per share) | $ / shares	$ 21.15
Modifications based on CrossFirst acquisition (in dollars per share) | $ / shares	20.43
Granted (in dollars per share) | $ / shares	20.99
Dividend equivalents earned (in dollars per share) | $ / shares	21.87
Vested (in dollars per share) | $ / shares	20.61
Forfeited (in dollars per share) | $ / shares	20.94
Non-vested at end of period (in dollars per share) | $ / shares	21.32
Vested and outstanding at end of period (in dollars per share) | $ / shares	$ 20.44
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	8,518
Vested (in shares) | shares	(44,039)
Non-vested at end of period (in shares) | shares	41,218
Vested and outstanding at end of period (in shares) | shares	146,076
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	22.64
Vested (in dollars per share) | $ / shares	23.29
Non-vested at end of period (in dollars per share) | $ / shares	22.16
Vested and outstanding at end of period (in dollars per share) | $ / shares	$ 23.01