STOCK-BASED COMPENSATION - Schedule of Changes in the Company's RSU, PSU, and DSU Awards (Details)	9 Months Ended
	Sep. 30, 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	366,487
Dividend equivalents earned (in shares) | shares	48,060
Vested (in shares) | shares	(451,041)
Forfeited (in shares) | shares	(133,212)
Non-vested at end of period (in shares) | shares	1,395,208
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	22.22
Dividend equivalents earned (in dollars per share) | $ / shares	22.30
Vested (in dollars per share) | $ / shares	20.03
Forfeited (in dollars per share) | $ / shares	22.38
Non-vested at end of period (in dollars per share) | $ / shares	$ 23.23
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	125
Vested (in shares) | shares	(6,131)
Forfeited (in shares) | shares	(45,878)
Non-vested at end of period (in shares) | shares	546,053
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	20.83
Vested (in dollars per share) | $ / shares	20.87
Forfeited (in dollars per share) | $ / shares	20.95
Non-vested at end of period (in dollars per share) | $ / shares	$ 21.29
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	6,447
Vested (in shares) | shares	(42,424)
Non-vested at end of period (in shares) | shares	40,762
Vested and outstanding at end of period (in shares) | shares	144,461
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	22.73
Vested (in dollars per share) | $ / shares	23.33
Non-vested at end of period (in dollars per share) | $ / shares	22.15
Vested and outstanding at end of period (in dollars per share) | $ / shares	$ 23.01