FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial assets:
Cash and due from banks	$ 255,312	$ 246,234
Federal funds sold and interest-bearing accounts	396,844	375,615
Time deposits in other banks	249	249
Loans, net	12,891,214	12,736,499
Accrued interest receivable	48,846	52,362
Financial liabilities:
Deposits	13,844,618	14,027,073
Securities sold under agreements to repurchase	15,160	20,635
Other borrowings	1,543,371	1,398,709
Subordinated deferrable interest debentures	122,890	127,560
FDIC loss-share payable	18,111	19,642
Accrued interest payable	11,133	11,524
Fair Value
Financial assets:
Cash and due from banks	255,312	246,234
Federal funds sold and interest-bearing accounts	396,844	375,615
Time deposits in other banks	249	249
Loans, net	12,949,045	12,806,709
Accrued interest receivable	48,846	52,362
Financial liabilities:
Deposits	13,851,760	14,035,686
Securities sold under agreements to repurchase	15,160	20,635
Other borrowings	1,549,322	1,402,510
Subordinated deferrable interest debentures	108,888	126,815
FDIC loss-share payable	18,360	19,657
Accrued interest payable	11,133	11,524
Fair Value | Level 1
Financial assets:
Cash and due from banks	255,312	246,234
Federal funds sold and interest-bearing accounts	396,844	375,615
Time deposits in other banks	0	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	15,160	20,635
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
FDIC loss-share payable	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	249
Loans, net	0	0
Accrued interest receivable	5,271	5,179
Financial liabilities:
Deposits	13,851,760	14,035,686
Securities sold under agreements to repurchase	0	0
Other borrowings	1,549,322	1,402,510
Subordinated deferrable interest debentures	108,888	126,815
FDIC loss-share payable	0	0
Accrued interest payable	11,133	11,524
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	0
Loans, net	12,949,045	12,806,709
Accrued interest receivable	43,575	47,183
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
FDIC loss-share payable	18,360	19,657
Accrued interest payable	$ 0	$ 0