FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial assets:
Cash and due from banks	$ 241,137	$ 284,567
Federal funds sold and interest-bearing accounts	1,304,636	833,565
Debt securities held-to-maturity	115,689	114,538
Financial liabilities:
Other borrowings	1,209,553	1,875,736
Subordinated deferrable interest debentures	129,817	128,322
Carrying Amount
Financial assets:
Cash and due from banks	241,137	284,567
Federal funds sold and interest-bearing accounts	1,304,636	833,565
Debt securities held-to-maturity	141,859	134,864
Loans, net	19,884,319	19,617,604
Accrued interest receivable	83,574	77,042
Financial liabilities:
Deposits	20,590,345	19,462,738
Other borrowings	1,209,553	1,875,736
Subordinated deferrable interest debentures	129,817	128,322
Accrued interest payable	38,836	10,530
Fair Value
Financial assets:
Cash and due from banks	241,137	284,567
Federal funds sold and interest-bearing accounts	1,304,636	833,565
Debt securities held-to-maturity	115,689	114,538
Loans, net	19,247,521	19,067,612
Accrued interest receivable	83,575	77,042
Financial liabilities:
Deposits	20,579,194	19,455,187
Other borrowings	1,189,399	1,861,850
Subordinated deferrable interest debentures	141,206	125,988
Accrued interest payable	38,836	10,530
Fair Value | Level 1
Financial assets:
Cash and due from banks	241,137	284,567
Federal funds sold and interest-bearing accounts	1,304,636	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	115,689	114,538
Loans, net	0	0
Accrued interest receivable	9,264	7,694
Financial liabilities:
Deposits	20,579,194	19,455,187
Other borrowings	1,189,399	1,861,850
Subordinated deferrable interest debentures	141,206	125,988
Accrued interest payable	38,836	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	19,247,521	19,067,612
Accrued interest receivable	74,311	69,348
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	$ 0	$ 0