FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financial assets:
Cash and due from banks	$ 131,071	$ 127,164
Federal funds sold and interest-bearing accounts	112,844	71,221
Loans, net	5,902,267	5,212,153
Accrued interest receivable	25,068	22,278
Financial liabilities:
Deposits	5,895,504	5,575,163
Securities sold under agreements to repurchase	14,156	53,505
Other borrowings	808,572	492,321
Subordinated deferrable interest debentures	85,220	84,228
FDIC loss-share payable	8,190	6,313	$ 7,775
Accrued interest payable	2,313	1,501
Fair Value
Financial assets:
Cash and due from banks	131,071	127,164
Federal funds sold and interest-bearing accounts	112,844	71,221
Loans, net	5,871,518	5,236,034
Accrued interest receivable	25,068	22,278
Financial liabilities:
Deposits	5,896,989	5,575,288
Securities sold under agreements to repurchase	14,156	53,505
Other borrowings	809,810	492,321
Subordinated deferrable interest debentures	70,984	67,321
FDIC loss-share payable	9,077	8,243
Accrued interest payable	2,313	1,501
Fair Value | Level 1
Financial assets:
Cash and due from banks	131,071	127,164
Federal funds sold and interest-bearing accounts	112,844	71,221
Loans, net	0	0
Accrued interest receivable	25,068	22,278
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	14,156	53,505
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
FDIC loss-share payable	0	0
Accrued interest payable	2,313	1,501
Fair Value | Level 2
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing accounts	0	0
Loans, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	5,896,989	5,575,288
Securities sold under agreements to repurchase	0	0
Other borrowings	809,810	492,321
Subordinated deferrable interest debentures	70,984	67,321
FDIC loss-share payable	0	0
Accrued interest payable	0	0
Fair Value | Level 3
Financial assets:
Cash and due from banks	0	0
Federal funds sold and interest-bearing accounts	0	0
Loans, net	5,871,518	5,236,034
Accrued interest receivable	0	0
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	9,077	8,243
Accrued interest payable	$ 0	$ 0