FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Financial assets:
Cash and due from banks	$ 284,552	$ 284,567
Federal funds sold and interest-bearing accounts	1,034,578	833,565
Debt securities held-to-maturity	121,891	114,538
Financial liabilities:
Other borrowings	1,536,989	1,875,736
Subordinated deferrable interest debentures	129,319	128,322
Carrying Amount
Financial assets:
Cash and due from banks	284,552	284,567
Federal funds sold and interest-bearing accounts	1,034,578	833,565
Debt securities held-to-maturity	142,513	134,864
Loans, net	20,172,786	19,617,604
Accrued interest receivable	77,360	77,042
Financial liabilities:
Deposits	20,443,125	19,462,738
Other borrowings	1,536,989	1,875,736
Subordinated deferrable interest debentures	129,319	128,322
Accrued interest payable	24,929	10,530
Fair Value
Financial assets:
Cash and due from banks	284,552	284,567
Federal funds sold and interest-bearing accounts	1,034,578	833,565
Debt securities held-to-maturity	121,891	114,538
Loans, net	19,515,996	19,067,612
Accrued interest receivable	77,360	77,042
Financial liabilities:
Deposits	20,452,110	19,455,187
Other borrowings	1,522,335	1,861,850
Subordinated deferrable interest debentures	141,225	125,988
Accrued interest payable	24,929	10,530
Fair Value | Level 1
Financial assets:
Cash and due from banks	284,552	284,567
Federal funds sold and interest-bearing accounts	1,034,578	833,565
Debt securities held-to-maturity	0	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	0	0
Fair Value | Level 2
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing accounts	0	0
Debt securities held-to-maturity	121,891	114,538
Loans, net	0	0
Accrued interest receivable	7,537	7,694
Financial liabilities:
Deposits	20,452,110	19,455,187
Other borrowings	1,522,335	1,861,850
Subordinated deferrable interest debentures	141,225	125,988
Accrued interest payable	24,929	10,530
Fair Value | Level 3
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing accounts	0	0
Debt securities held-to-maturity	0
Loans, net	19,515,996	19,067,612
Accrued interest receivable	69,823	69,348
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	$ 0	$ 0