FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 144,801	$ 172,036
Federal funds sold and interest-bearing deposits in banks	712,199	507,491
Time deposits in other banks	7,371	10,812
Loans, net	8,422,283	8,454,442
Accrued interest receivable	37,411	36,970
Financial liabilities:
Deposits	9,800,875	9,649,313
Securities sold under agreements to repurchase	4,259	20,384
Other borrowings	151,454	151,774
Subordinated deferrable interest debentures	89,529	89,187
FDIC loss-share payable	18,834	19,487
Accrued interest payable	5,462	5,669
Fair Value
Financial assets:
Cash and due from banks	144,801	172,036
Federal funds sold and interest-bearing deposits in banks	712,199	507,491
Time deposits in other banks	7,371	10,812
Loans, net	8,357,110	8,365,293
Accrued interest receivable	37,411	36,970
Financial liabilities:
Deposits	9,797,905	9,645,617
Securities sold under agreements to repurchase	4,259	20,384
Other borrowings	152,655	152,873
Subordinated deferrable interest debentures	88,900	90,180
FDIC loss-share payable	18,847	19,576
Accrued interest payable	5,462	5,669
Fair Value | Level 1
Financial assets:
Cash and due from banks	144,801	172,036
Federal funds sold and interest-bearing deposits in banks	712,199	507,491
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	4,259	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	7,371	10,812
Loans, net	0	0
Accrued interest receivable	5,366	5,456
Financial liabilities:
Deposits	9,797,905	9,645,617
Securities sold under agreements to repurchase	0	0
Other borrowings	152,655	152,873
Subordinated deferrable interest debentures	88,900	90,180
FDIC loss-share payable	0	0
Accrued interest payable	5,462	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, net	8,357,110	8,365,293
Accrued interest receivable	32,045	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	18,847	19,576
Accrued interest payable	$ 0	$ 0