STOCK-BASED COMPENSATION - Schedule of Changes in the Company's RSU, PSU, and DSU Awards (Details)	3 Months Ended
	Mar. 31, 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	348,269
Dividend equivalents earned (in shares) | shares	10,984
Vested (in shares) | shares	(1,796)
Forfeited (in shares) | shares	(90,812)
Non-vested at end of period (in shares) | shares	1,831,559
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	24.48
Vested (in dollars per share) | $ / shares	23.99
Forfeited (in dollars per share) | $ / shares	21.85
Non-vested at end of period (in dollars per share) | $ / shares	$ 22.47
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
Forfeited (in shares) | shares	(21,180)
Non-vested at end of period (in shares) | shares	576,757
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	22.15
Forfeited (in dollars per share) | $ / shares	21.12
Non-vested at end of period (in dollars per share) | $ / shares	$ 22.08
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	2,284
Vested (in shares) | shares	(39,177)
Non-vested at end of period (in shares) | shares	39,846
Vested and outstanding at end of period (in shares) | shares	141,214
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	24.28
Vested (in dollars per share) | $ / shares	23.45
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	$ 23.04