FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 151,186	$ 172,036
Federal funds sold and interest-bearing deposits in banks	186,969	507,491
Time deposits in other banks	748	10,812
Loans held for sale	64,773
Loans, net	8,987,091	8,454,442
Accrued interest receivable	36,719	36,970
Financial liabilities:
Deposits	9,582,370	9,649,313
Securities sold under agreements to repurchase	3,307	20,384
Other borrowings	564,636	151,774
Subordinated deferrable interest debentures	89,871	89,187
FDIC loss-share payable	20,596	19,487
Accrued interest payable	7,330	5,669
Fair Value
Financial assets:
Cash and due from banks	151,186	172,036
Federal funds sold and interest-bearing deposits in banks	186,969	507,491
Time deposits in other banks	748	10,812
Loans held for sale	64,773
Loans, net	9,011,842	8,365,293
Accrued interest receivable	36,719	36,970
Financial liabilities:
Deposits	9,580,642	9,645,617
Securities sold under agreements to repurchase	3,307	20,384
Other borrowings	565,992	152,873
Subordinated deferrable interest debentures	86,744	90,180
FDIC loss-share payable	20,590	19,576
Accrued interest payable	7,330	5,669
Fair Value | Level 1
Financial assets:
Cash and due from banks	151,186	172,036
Federal funds sold and interest-bearing deposits in banks	186,969	507,491
Time deposits in other banks	0	0
Loans held for sale	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	3,307	20,384
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 deposits in banks	0	0
Time deposits in other banks	748	10,812
Loans held for sale	64,773
Loans, net	0	0
Accrued interest receivable	4,849	5,456
Financial liabilities:
Deposits	9,580,642	9,645,617
Securities sold under agreements to repurchase	0	0
Other borrowings	565,992	152,873
Subordinated deferrable interest debentures	86,744	90,180
FDIC loss-share payable	0	0
Accrued interest payable	7,330	5,669
Fair Value | Level 3
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing deposits in banks	0	0
Time deposits in other banks	0	0
Loans held for sale	0
Loans, net	9,011,842	8,365,293
Accrued interest receivable	31,870	31,514
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	20,590	19,576
Accrued interest payable	$ 0	$ 0