FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial assets:
Cash and due from banks	$ 123,945	$ 139,313
Federal funds sold and interest-bearing accounts	210,930	191,345
Loans, net	6,137,838	5,992,880
Accrued interest receivable	24,818	26,005
Financial liabilities:
Deposits	6,446,165	6,625,845
Securities sold under agreements to repurchase	23,270	30,638
Other borrowings	555,535	250,554
Subordinated deferrable interest debentures	85,881	85,550
FDIC loss-share payable	9,255	8,803
Liability for USPF acquisition contingent consideration	5,719
Accrued interest payable	2,367	3,258
Fair Value
Financial assets:
Cash and due from banks	123,945	139,313
Federal funds sold and interest-bearing accounts	210,930	191,345
Loans, net	6,127,411	5,960,963
Accrued interest receivable	24,818	26,005
Financial liabilities:
Deposits	6,447,150	6,627,773
Securities sold under agreements to repurchase	23,270	30,638
Other borrowings	556,707	251,759
Subordinated deferrable interest debentures	80,266	74,243
FDIC loss-share payable	9,880	9,548
Liability for USPF acquisition contingent consideration	5,719
Accrued interest payable	2,367	3,258
Fair Value | Level 1
Financial assets:
Cash and due from banks	123,945	139,313
Federal funds sold and interest-bearing accounts	210,930	191,345
Loans, net	0	0
Accrued interest receivable	24,818	26,005
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	23,270	30,638
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
FDIC loss-share payable	0	0
Liability for USPF acquisition contingent consideration	0
Accrued interest payable	2,367	3,258
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	6,447,150	6,627,773
Securities sold under agreements to repurchase	0	0
Other borrowings	556,707	271,759
Subordinated deferrable interest debentures	80,266	74,243
FDIC loss-share payable	0	0
Liability for USPF acquisition contingent consideration	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	6,127,411	5,960,963
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	9,880	9,548
Liability for USPF acquisition contingent consideration	5,719
Accrued interest payable	$ 0	$ 0