FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financial assets:
Cash and due from banks	$ 307,813	$ 203,349
Time deposits in other banks	0	249
Financial liabilities:
Other borrowings	739,879	425,155
Subordinated deferrable interest debentures	126,328	124,345
Carrying Amount
Financial assets:
Cash and due from banks	307,813	203,349
Federal funds sold and interest-bearing accounts	3,756,844	1,913,957
Time deposits in other banks		249
Debt securities held-to-maturity	79,850
Loans, net	15,662,495	14,183,077
Accrued interest receivable	56,917	76,254
Financial liabilities:
Deposits	19,665,553	16,957,823
Securities sold under agreements to repurchase	5,845	11,641
Other borrowings	739,879	425,155
Subordinated deferrable interest debentures	126,328	124,345
Accrued interest payable	4,313	5,487
Fair Value
Financial assets:
Cash and due from banks	307,813	203,349
Federal funds sold and interest-bearing accounts	3,756,844	1,913,957
Time deposits in other banks		249
Debt securities held-to-maturity	78,206
Loans, net	15,509,410	14,096,711
Accrued interest receivable	56,917	76,254
Financial liabilities:
Deposits	19,667,612	16,968,606
Securities sold under agreements to repurchase	5,845	11,641
Other borrowings	760,829	431,783
Subordinated deferrable interest debentures	117,764	116,280
Accrued interest payable	4,313	5,487
Fair Value | Level 1
Financial assets:
Cash and due from banks	307,813	203,349
Federal funds sold and interest-bearing accounts	3,756,844	1,913,957
Time deposits in other banks		0
Debt securities held-to-maturity	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	5,845	11,641
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
Time deposits in other banks		249
Debt securities held-to-maturity	78,206
Loans, net	0	0
Accrued interest receivable	2,373	3,567
Financial liabilities:
Deposits	19,667,612	16,968,606
Securities sold under agreements to repurchase	0	0
Other borrowings	760,829	431,783
Subordinated deferrable interest debentures	117,764	116,280
Accrued interest payable	4,313	5,487
Fair Value | Level 3
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing accounts	0	0
Time deposits in other banks		0
Debt securities held-to-maturity	0
Loans, net	15,509,410	14,096,711
Accrued interest receivable	54,544	72,687
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
Accrued interest payable	$ 0	$ 0