0000001 - Document - Cover Page link:presentationLink link:calculationLink link:definitionLink 0000002 - Statement - CONSOLIDATED BALANCE SHEETS (Unaudited) link:presentationLink link:calculationLink link:definitionLink 0000003 - Statement - CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 0000004 - Statement - CONSOLIDATED STATEMENTS OF INCOME (Unaudited) link:presentationLink link:calculationLink link:definitionLink 0000005 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) link:presentationLink link:calculationLink link:definitionLink 0000006 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 0000007 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) link:presentationLink link:calculationLink link:definitionLink 0000008 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 0000009 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) link:presentationLink link:calculationLink link:definitionLink 0000010 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES link:presentationLink link:calculationLink link:definitionLink 0000011 - Disclosure - DEBT SECURITIES link:presentationLink link:calculationLink link:definitionLink 0000012 - Disclosure - PORTFOLIO LOANS link:presentationLink link:calculationLink link:definitionLink 0000013 - Disclosure - LEASES link:presentationLink link:calculationLink link:definitionLink 0000014 - Disclosure - DEPOSITS link:presentationLink link:calculationLink link:definitionLink 0000015 - Disclosure - BORROWINGS link:presentationLink link:calculationLink link:definitionLink 0000016 - Disclosure - REGULATORY CAPITAL link:presentationLink link:calculationLink link:definitionLink 0000017 - Disclosure - TAX CREDIT AND OTHER INVESTMENTS IN UNCONSOLIDATED ENTITIES link:presentationLink link:calculationLink link:definitionLink 0000018 - Disclosure - STOCK-BASED COMPENSATION link:presentationLink link:calculationLink link:definitionLink 0000019 - Disclosure - OUTSTANDING COMMITMENTS AND CONTINGENT LIABILITIES link:presentationLink link:calculationLink link:definitionLink 0000020 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS link:presentationLink link:calculationLink link:definitionLink 0000021 - Disclosure - FAIR VALUE MEASUREMENTS link:presentationLink link:calculationLink link:definitionLink 0000022 - Disclosure - EARNINGS PER COMMON SHARE link:presentationLink link:calculationLink link:definitionLink 0000023 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) link:presentationLink link:calculationLink link:definitionLink 0000024 - Disclosure - OPERATING SEGMENTS AND RELATED INFORMATION link:presentationLink link:calculationLink link:definitionLink 0000025 - Disclosure - ACQUISITION link:presentationLink link:calculationLink link:definitionLink 9954471 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES (Policies) link:presentationLink link:calculationLink link:definitionLink 9954472 - Disclosure - DEBT SECURITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 9954473 - Disclosure - PORTFOLIO LOANS (Tables) link:presentationLink link:calculationLink link:definitionLink 9954474 - Disclosure - LEASES (Tables) link:presentationLink link:calculationLink link:definitionLink 9954475 - Disclosure - DEPOSITS (Tables) link:presentationLink link:calculationLink link:definitionLink 9954476 - Disclosure - BORROWINGS (Tables) link:presentationLink link:calculationLink link:definitionLink 9954477 - Disclosure - REGULATORY CAPITAL (Tables) link:presentationLink link:calculationLink link:definitionLink 9954478 - Disclosure - TAX CREDIT AND OTHER INVESTMENTS IN UNCONSOLIDATED ENTITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 9954479 - Disclosure - STOCK-BASED COMPENSATION (Tables) link:presentationLink link:calculationLink link:definitionLink 9954480 - Disclosure - OUTSTANDING COMMITMENTS AND CONTINGENT LIABILITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 9954481 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS (Tables) link:presentationLink link:calculationLink link:definitionLink 9954482 - Disclosure - FAIR VALUE MEASUREMENTS (Tables) link:presentationLink link:calculationLink link:definitionLink 9954483 - Disclosure - EARNINGS PER COMMON SHARE (Tables) link:presentationLink link:calculationLink link:definitionLink 9954484 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables) link:presentationLink link:calculationLink link:definitionLink 9954485 - Disclosure - OPERATING SEGMENTS AND RELATED INFORMATION (Tables) link:presentationLink link:calculationLink link:definitionLink 9954486 - Disclosure - SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954487 - Disclosure - DEBT SECURITIES - Schedule of Amortized Cost, Unrealized Gains and Losses, and Fair Values of Securities Classified as AFS and HTM (Details) link:presentationLink link:calculationLink link:definitionLink 9954488 - Disclosure - DEBT SECURITIES - Maturity of Debt Securities (Details) link:presentationLink link:calculationLink link:definitionLink 9954489 - Disclosure - DEBT SECURITIES - Schedule of Realized Gains and Losses on Debt Securities (Details) link:presentationLink link:calculationLink link:definitionLink 9954490 - Disclosure - DEBT SECURITIES - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954491 - Disclosure - DEBT SECURITIES - Debt securities in an unrealized loss position (Details) link:presentationLink link:calculationLink link:definitionLink 9954492 - Disclosure - DEBT SECURITIES - Additional Information on Debt Securities In Unrealized or Unrecognized Loss Position (Details) link:presentationLink link:calculationLink link:definitionLink 9954493 - Disclosure - PORTFOLIO LOANS - Distribution of portfolio loans (Details) link:presentationLink link:calculationLink link:definitionLink 9954494 - Disclosure - PORTFOLIO LOANS - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954495 - Disclosure - PORTFOLIO LOANS - Schedule of financial instruments owned and pledged as collateral (Details) link:presentationLink link:calculationLink link:definitionLink 9954496 - Disclosure - PORTFOLIO LOANS - Summary of risk grades segregated by category of portfolio loans (Details) link:presentationLink link:calculationLink link:definitionLink 9954497 - Disclosure - PORTFOLIO LOANS - Risk grades of portfolio loans, further sorted by origination year (Details) link:presentationLink link:calculationLink link:definitionLink 9954498 - Disclosure - PORTFOLIO LOANS -Summary of portfolio loans that are past due and still accruing or on a non-accrual status (Details) link:presentationLink link:calculationLink link:definitionLink 9954499 - Disclosure - PORTFOLIO LOANS - Schedule of loan modifications made to borrowers experiencing financial difficulty (Details) link:presentationLink link:calculationLink link:definitionLink 9954500 - Disclosure - PORTFOLIO LOANS - Summary of the financial effect of modifications (Details) link:presentationLink link:calculationLink link:definitionLink 9954501 - Disclosure - PORTFOLIO LOANS - Schedule of payment status of modified loans (Details) link:presentationLink link:calculationLink link:definitionLink 9954502 - Disclosure - PORTFOLIO LOANS - Schedule of details of impaired loans, segregated by category (Details) link:presentationLink link:calculationLink link:definitionLink 9954503 - Disclosure - PORTFOLIO LOANS - Schedule of activity on the allowance for loan losses (Details) link:presentationLink link:calculationLink link:definitionLink 9954504 - Disclosure - PORTFOLIO LOANS - Schedule of allowance for loan losses and recorded investments in portfolio loans, by category (Details) link:presentationLink link:calculationLink link:definitionLink 9954505 - Disclosure - LEASES - Summary of lease-related balances (Details) link:presentationLink link:calculationLink link:definitionLink 9954506 - Disclosure - LEASES - Schedule of lease costs and other lease information (Details) link:presentationLink link:calculationLink link:definitionLink 9954507 - Disclosure - LEASES - Schedule of future undiscounted lease payments (Details) link:presentationLink link:calculationLink link:definitionLink 9954507 - Disclosure - LEASES - Schedule of future undiscounted lease payments (Details) link:presentationLink link:calculationLink link:definitionLink 9954508 - Disclosure - LEASES - Summary of revenue recorded in connection with leases (Details) link:presentationLink link:calculationLink link:definitionLink 9954509 - Disclosure - DEPOSITS - Schedule of composition of deposits (Details) link:presentationLink link:calculationLink link:definitionLink 9954510 - Disclosure - DEPOSITS - Schedule of maturities of time deposits (Details) link:presentationLink link:calculationLink link:definitionLink 9954511 - Disclosure - BORROWINGS - Schedule of distribution of securities sold under agreements to repurchase and short-term borrowings and weighted average interest rates (Details) link:presentationLink link:calculationLink link:definitionLink 9954512 - Disclosure - BORROWINGS - Term Loan (Details) link:presentationLink link:calculationLink link:definitionLink 9954513 - Disclosure - BORROWINGS - Schedule of Short-term Borrowings (Details) link:presentationLink link:calculationLink link:definitionLink 9954514 - Disclosure - BORROWINGS - Summary of Long-term Debt (Details) link:presentationLink link:calculationLink link:definitionLink 9954515 - Disclosure - BORROWINGS - Subordinated Notes (Details) link:presentationLink link:calculationLink link:definitionLink 9954516 - Disclosure - BORROWINGS - Schedule of unamortized debt issuance cost (Details) link:presentationLink link:calculationLink link:definitionLink 9954517 - Disclosure - REGULATORY CAPITAL - Capital Amounts and Ratios (Details) link:presentationLink link:calculationLink link:definitionLink 9954518 - Disclosure - TAX CREDIT AND OTHER INVESTMENTS IN UNCONSOLIDATED ENTITIES - Schedule of Impact of the Busey's other asset investments (Details) link:presentationLink link:calculationLink link:definitionLink 9954519 - Disclosure - STOCK-BASED COMPENSATION - Summary of changes in the Company's stock option awards (Details) link:presentationLink link:calculationLink link:definitionLink 9954520 - Disclosure - STOCK-BASED COMPENSATION - 2020 Equity Plan (Details) link:presentationLink link:calculationLink link:definitionLink 9954521 - Disclosure - STOCK-BASED COMPENSATION - RSU, PSU, and DSU Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954522 - Disclosure - STOCK-BASED COMPENSATION - Summary of changes in the Company's RSU, PSU, and DSU awards (Details) link:presentationLink link:calculationLink link:definitionLink 9954523 - Disclosure - STOCK-BASED COMPENSATION - 2021 Employee Stock Purchase Plan and Stock-based Compensation Expense (Details) link:presentationLink link:calculationLink link:definitionLink 9954524 - Disclosure - STOCK-BASED COMPENSATION - Schedule of Stock-based compensation expense (Details) link:presentationLink link:calculationLink link:definitionLink 9954525 - Disclosure - STOCK-BASED COMPENSATION - Schedule of Unamortized stock-based compensation expense (Details) link:presentationLink link:calculationLink link:definitionLink 9954526 - Disclosure - OUTSTANDING COMMITMENTS AND CONTINGENT LIABILITIES (Details) link:presentationLink link:calculationLink link:definitionLink 9954527 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of financial instruments owned and pledged as collateral (Details) link:presentationLink link:calculationLink link:definitionLink 9954528 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954529 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Summary of the interest-rate swaps designated as cash flow hedges (Details) link:presentationLink link:calculationLink link:definitionLink 9954530 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Reclassification of unrealized gains and losses from OCI (Details) link:presentationLink link:calculationLink link:definitionLink 9954531 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of interest income (expense) recorded on swap transactions (Details) link:presentationLink link:calculationLink link:definitionLink 9954532 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Net Gains (Losses) Recorded in Accumulated Other Comprehensive Income (Loss) (Details) link:presentationLink link:calculationLink link:definitionLink 9954533 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Interest Rate Swaps Not Designated as Hedges (Details) link:presentationLink link:calculationLink link:definitionLink 9954534 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Interest Rate Swaps Recorded in Noninterest Expense (Details) link:presentationLink link:calculationLink link:definitionLink 9954535 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Risk Participation Agreement (Details) link:presentationLink link:calculationLink link:definitionLink 9954536 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Mortgage Banking Derivatives (Details) link:presentationLink link:calculationLink link:definitionLink 9954537 - Disclosure - DERIVATIVE FINANCIAL INSTRUMENTS - Net Gains (Losses) Relating to Derivative Instruments (Details) link:presentationLink link:calculationLink link:definitionLink 9954538 - Disclosure - FAIR VALUE MEASUREMENTS - Schedule of financial assets and financial liabilities measured at fair value on a recurring basis (Details) link:presentationLink link:calculationLink link:definitionLink 9954539 - Disclosure - FAIR VALUE MEASUREMENTS - Schedule of assets and liabilities measured at fair value on a non-recurring basis (Details) link:presentationLink link:calculationLink link:definitionLink 9954540 - Disclosure - FAIR VALUE MEASUREMENTS - Schedule of quantitative information about Level 3 fair value measurements (Details) link:presentationLink link:calculationLink link:definitionLink 9954541 - Disclosure - FAIR VALUE MEASUREMENTS - Schedule of estimated fair values of financial instruments (Details) link:presentationLink link:calculationLink link:definitionLink 9954542 - Disclosure - EARNINGS PER COMMON SHARE - Schedule of computation of earnings per common share (Details) link:presentationLink link:calculationLink link:definitionLink 9954543 - Disclosure - EARNINGS PER COMMON SHARE - Schedule of average shares excluded from computation of diluted earnings per common share (Details) link:presentationLink link:calculationLink link:definitionLink 9954544 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) link:presentationLink link:calculationLink link:definitionLink 9954545 - Disclosure - OPERATING SEGMENTS AND RELATED INFORMATION - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954546 - Disclosure - OPERATING SEGMENTS AND RELATED INFORMATION - Summary of information relating to operating segments (Details) link:presentationLink link:calculationLink link:definitionLink 9954547 - Disclosure - ACQUISITION (Details) link:presentationLink link:calculationLink link:definitionLink