FAIR VALUE MEASURES - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial assets:
Cash and due from banks	$ 172,036	$ 139,313
Time deposits in other banks	10,812	0
Financial liabilities:
Other borrowings	151,774	250,554
Subordinated deferrable interest debentures	89,187	85,550
FDIC loss-share payable	19,487	8,803
Carrying Amount
Financial assets:
Cash and due from banks	172,036	139,313
Federal funds sold and interest-bearing accounts	507,491	191,345
Time deposits in other banks	10,812
Loans, net	8,454,442	5,992,880
Accrued interest receivable	36,970	26,005
Financial liabilities:
Deposits	9,649,313	6,625,845
Securities sold under agreements to repurchase	20,384	30,638
Other borrowings	151,774	250,554
Subordinated deferrable interest debentures	89,187	85,550
FDIC loss-share payable	19,487	8,803
Accrued interest payable	5,669	3,258
Fair Value
Financial assets:
Cash and due from banks	172,036	139,313
Federal funds sold and interest-bearing accounts	507,491	191,345
Time deposits in other banks	10,812
Loans, net	8,365,293	5,960,963
Accrued interest receivable	36,970	26,005
Financial liabilities:
Deposits	9,645,617	6,627,773
Securities sold under agreements to repurchase	20,384	30,638
Other borrowings	152,873	251,759
Subordinated deferrable interest debentures	90,180	74,243
FDIC loss-share payable	19,576	9,548
Accrued interest payable	5,669	3,258
Fair Value | Level 1
Financial assets:
Cash and due from banks	172,036	139,313
Federal funds sold and interest-bearing accounts	507,491	191,345
Time deposits in other banks	0
Loans, net	0	0
Accrued interest receivable	0	26,005
Financial liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	20,384	30,638
Other borrowings	0	0
Subordinated deferrable interest debentures	0	0
FDIC loss-share payable	0	0
Accrued interest payable	0	3,258
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	10,812
Loans, net	0	0
Accrued interest receivable	5,456	0
Financial liabilities:
Deposits	9,645,617	6,627,773
Securities sold under agreements to repurchase	0	0
Other borrowings	152,873	271,759
Subordinated deferrable interest debentures	90,180	74,243
FDIC loss-share payable	0	0
Accrued interest payable	5,669	0
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
Loans, net	8,365,293	5,960,963
Accrued interest receivable	31,514	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	19,576	9,548
Accrued interest payable	$ 0	$ 0