FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financial assets:
Cash and due from banks	$ 345,627	$ 307,813
Federal funds sold and interest-bearing accounts	1,961,209	3,756,844
Debt securities held-to-maturity	97,144	78,206
Financial liabilities:
Other borrowings	425,592	739,879
Subordinated deferrable interest debentures	127,325	126,328
Carrying Amount
Financial assets:
Cash and due from banks	345,627	307,813
Federal funds sold and interest-bearing accounts	1,961,209	3,756,844
Debt securities held-to-maturity	111,654	79,850
Loans, net	17,352,347	15,662,495
Accrued interest receivable	56,995	56,917
Financial liabilities:
Deposits	19,684,982	19,665,553
Securities sold under agreements to repurchase	953	5,845
Other borrowings	425,592	739,879
Subordinated deferrable interest debentures	127,325	126,328
Accrued interest payable	2,875	4,313
Fair Value
Financial assets:
Cash and due from banks	345,627	307,813
Federal funds sold and interest-bearing accounts	1,961,209	3,756,844
Debt securities held-to-maturity	97,144	78,206
Loans, net	17,056,635	15,509,410
Accrued interest receivable	56,995	56,917
Financial liabilities:
Deposits	19,682,653	19,667,612
Securities sold under agreements to repurchase	953	5,845
Other borrowings	418,722	760,829
Subordinated deferrable interest debentures	117,240	117,764
Accrued interest payable	2,875	4,313
Fair Value | Level 1
Financial assets:
Cash and due from banks	345,627	307,813
Federal funds sold and interest-bearing accounts	1,961,209	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	953	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	97,144	78,206
Loans, net	0	0
Accrued interest receivable	3,867	2,373
Financial liabilities:
Deposits	19,682,653	19,667,612
Securities sold under agreements to repurchase	0	0
Other borrowings	418,722	760,829
Subordinated deferrable interest debentures	117,240	117,764
Accrued interest payable	2,875	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	17,056,635	15,509,410
Accrued interest receivable	53,128	54,544
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