FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis

The following tables summarize financial assets and financial liabilities measured at estimated fair value on a recurring basis:

	As of December 31, 2025
(dollars in thousands)	Level 1 Inputs		Level 2 Inputs		Level 3 Inputs		Total Fair Value
Debt securities available for sale:
Obligations of U.S. government corporations and agencies	$	—	$	112,046	$	—	$	112,046
Obligations of states and political subdivisions	—		263,873		—		263,873
Asset-backed securities	—		265,580		—		265,580
Commercial mortgage-backed securities	—		132,942		—		132,942
Residential mortgage-backed securities	—		1,344,416		—		1,344,416
Corporate debt securities	—		43,691		—		43,691
Equity securities	155		14,761		—		14,916
Derivative assets	—		30,902		30		30,932
Derivative liabilities	—		42,155		65		42,220

	As of December 31, 2024
(dollars in thousands)	Level 1 Inputs		Level 2 Inputs		Level 3 Inputs		Total Fair Value
Debt securities available for sale:
Obligations of U.S. government corporations and agencies	$	—	$	1,400	$	—	$	1,400
Obligations of states and political subdivisions	—		139,829		—		139,829
Asset-backed securities	—		336,557		—		336,557
Commercial mortgage-backed securities	—		92,174		—		92,174
Residential mortgage-backed securities	—		1,087,210		—		1,087,210
Corporate debt securities	—		153,051		—		153,051
Equity securities	5,567		10,295		—		15,862
Derivative assets	—		30,368		5		30,373
Derivative liabilities	—		58,099		—		58,099

Activity for risk participation agreements, which are financial assets measured at estimated fair value on a recurring basis using Level 3, is summarized in the tables below:

		Years Ended December 31,
(dollars in thousands)	Location	2025		2024
Beginning Balance		$	5	$	15
Gains (losses) recognized in earnings	Other expense	117		(26)
Purchases		(171)		16
Sales		55		—
Assumed in acquisition		(41)		—
Ending Balance		$	(35)	$	5

Schedule of Assets and Liabilities Measured at Fair Value on a Non-Recurring Basis

The following tables summarize assets and liabilities measured at estimated fair value on a non-recurring basis:

	As of December 31, 2025
(dollars in thousands)	Level 1 Inputs		Level 2 Inputs		Level 3 Inputs		Total Fair Value
Loans evaluated individually, net of related allowance	$	—	$	—	$	19,604	$	19,604
OREO and other repossessed assets with subsequent impairment	—		—		4,409		4,409
Bank property held for sale with impairment	—		—		1,855		1,855

	As of December 31, 2024
(dollars in thousands)	Level 1 Inputs		Level 2 Inputs		Level 3 Inputs		Total Fair Value
Loans evaluated individually, net of related allowance	$	—	$	—	$	616	$	616
Bank property held for sale with impairment	—		—		2,841		2,841

Schedule of Quantitative Information About Level 3 Fair Value Measurements

The following tables present additional quantitative information about assets measured at estimated fair value on a non-recurring basis using Level 3 inputs:

	As of December 31, 2025
(dollars in thousands)	Fair Value		Valuation Techniques	Unobservable Input	Range (Weighted Average)
Loans evaluated individually, net of related allowance	$	19,604	Appraisal of collateral	Appraisal adjustments	-1.6% to -100.0% (-44.6)
OREO and other repossessed assets with subsequent impairment	4,409		Appraisal of collateral	Appraisal adjustments	-2.8% to -24.1% (-4.5)%
Bank property held for sale with impairment	1,855		Appraisal of collateral or real estate listing price	Appraisal adjustments	-9.0% to -58.0% (-39.4)

	As of December 31, 2024
(dollars in thousands)	Fair Value		Valuation Techniques	Unobservable Input	Range (Weighted Average)
Loans evaluated individually, net of related allowance	$	616	Appraisal of collateral	Appraisal adjustments	-25.0% to -100.0% (-74.9)%
Bank property held for sale with impairment	2,841		Appraisal of collateral or real estate listing price	Appraisal adjustments	-9.0% to -76.7% (-51.8)%

Schedule of Estimated Fair Values of Financial Instruments

Fair values of financial instruments that are not carried at fair value on Busey’s Consolidated Balance Sheets were estimated as follows:

	As of December 31, 2025				As of December 31, 2024
(dollars in thousands)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Financial assets
Level 1 inputs:
Cash and cash equivalents	$	294,052	$	294,052	$	697,659	$	697,659
Level 2 inputs:
Debt securities held to maturity	746,385		625,957		826,630		675,053
Loans held for sale	5,752		5,886		3,657		3,726
Restricted bank stock	77,006		77,006		49,930		49,930
Accrued interest receivable	71,788		71,788		45,141		45,141
Level 3 inputs:
Portfolio loans, net	13,393,776		13,472,907		7,613,683		7,426,158
Mortgage servicing rights	1,459		5,176		1,304		5,627
Other servicing rights	2,086		2,193		1,482		1,591
Financial liabilities
Level 2 inputs:
Time deposits	$	2,429,890	$	2,425,290	$	1,490,635	$	1,481,591
Securities sold under agreements to repurchase	166,929		166,929		155,610		155,610
Long-term borrowings	113,806		113,853		—		—
Junior subordinated debt owed to unconsolidated trusts	77,328		71,407		74,815		67,314
Accrued interest payable	25,372		25,372		21,129		21,129
Level 3 inputs:
Subordinated notes, net of unamortized issuance costs	99,395		94,500		227,723		219,043