FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Financial assets:
Cash and due from banks	$ 266,400	$ 284,567
Federal funds sold and interest-bearing accounts	1,754,453	833,565
Debt securities held-to-maturity	116,093	114,538
Financial liabilities:
Other borrowings	2,401,327	1,875,736
Subordinated deferrable interest debentures	128,820	128,322
Carrying Amount
Financial assets:
Cash and due from banks	266,400	284,567
Federal funds sold and interest-bearing accounts	1,754,453	833,565
Debt securities held-to-maturity	134,175	134,864
Loans, net	19,707,011	19,617,604
Accrued interest receivable	74,698	77,042
Financial liabilities:
Deposits	19,897,455	19,462,738
Other borrowings	2,401,327	1,875,736
Subordinated deferrable interest debentures	128,820	128,322
Accrued interest payable	18,005	10,530
Fair Value
Financial assets:
Cash and due from banks	266,400	284,567
Federal funds sold and interest-bearing accounts	1,754,453	833,565
Debt securities held-to-maturity	116,093	114,538
Loans, net	19,076,408	19,067,612
Accrued interest receivable	74,698	77,042
Financial liabilities:
Deposits	19,855,914	19,455,187
Other borrowings	2,371,530	1,861,850
Subordinated deferrable interest debentures	124,309	125,988
Accrued interest payable	18,005	10,530
Fair Value | Level 1
Financial assets:
Cash and due from banks	266,400	284,567
Federal funds sold and interest-bearing accounts	1,754,453	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	116,093	114,538
Loans, net	0	0
Accrued interest receivable	6,736	7,694
Financial liabilities:
Deposits	19,855,914	19,455,187
Other borrowings	2,371,530	1,861,850
Subordinated deferrable interest debentures	124,309	125,988
Accrued interest payable	18,005	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	19,076,408	19,067,612
Accrued interest receivable	67,962	69,348
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	$ 0	$ 0