FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Financial assets:
Cash and due from banks	$ 269,193	$ 307,813
Federal funds sold and interest-bearing accounts	1,061,975	3,756,844
Debt securities held-to-maturity	107,814	78,206
Financial liabilities:
Other borrowings	725,664	739,879
Subordinated deferrable interest debentures	127,823	126,328
Carrying Amount
Financial assets:
Cash and due from banks	269,193	307,813
Federal funds sold and interest-bearing accounts	1,061,975	3,756,844
Debt securities held-to-maturity	130,214	79,850
Loans, net	18,591,951	15,662,495
Accrued interest receivable	61,828	56,917
Financial liabilities:
Deposits	19,466,919	19,665,553
Securities sold under agreements to repurchase		5,845
Other borrowings	725,664	739,879
Subordinated deferrable interest debentures	127,823	126,328
Accrued interest payable	5,628	4,313
Fair Value
Financial assets:
Cash and due from banks	269,193	307,813
Federal funds sold and interest-bearing accounts	1,061,975	3,756,844
Debt securities held-to-maturity	107,814	78,206
Loans, net	18,289,190	15,509,410
Accrued interest receivable	61,828	56,917
Financial liabilities:
Deposits	19,463,748	19,667,612
Securities sold under agreements to repurchase		5,845
Other borrowings	712,395	760,829
Subordinated deferrable interest debentures	120,121	117,764
Accrued interest payable	5,628	4,313
Fair Value | Level 1
Financial assets:
Cash and due from banks	269,193	307,813
Federal funds sold and interest-bearing accounts	1,061,975	3,756,844
Debt securities held-to-maturity	0	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase		5,845
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	107,814	78,206
Loans, net	0	0
Accrued interest receivable	6,436	2,373
Financial liabilities:
Deposits	19,463,748	19,667,612
Securities sold under agreements to repurchase		0
Other borrowings	712,395	760,829
Subordinated deferrable interest debentures	120,121	117,764
Accrued interest payable	5,628	4,313
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	0
Loans, net	18,289,190	15,509,410
Accrued interest receivable	55,392	54,544
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase		0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	$ 0	$ 0