FAIR VALUE - Summary of Estimated Fair Values and Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 71,292	$ 142,145
Interest-bearing deposits with banks	87,349	153,223
Securities available for sale	642,897	680,886
Securities held to maturity	145,480	156,792
Accrued interest receivable	12,397	11,236
Carrying Amount
Financial assets:
Cash and due from banks	71,292	142,145
Interest-bearing deposits with banks	87,349	153,223
Securities available for sale	642,897	680,886
Securities restricted	24,104	24,028
Securities held to maturity	144,716	160,163
Loans held for sale	12,643
Loans, net	3,398,852	3,244,393
Derivatives	11,919	6,363
Accrued interest receivable	12,397	11,236
Financial liabilities:
Certificates of deposit	276,921	329,491
Demand and other deposits	3,559,655	3,556,902
FHLB advances	240,000	240,433
Repurchase agreements	945	539
Subordinated debentures	78,850	78,781
Derivatives	13,594	2,215
Accrued interest payable	1,718	1,524
Fair Value
Financial assets:
Cash and due from banks	71,292	142,145
Interest-bearing deposits with banks	87,349	153,223
Securities available for sale	642,897	680,886
Securities held to maturity	145,480	156,792
Loans held for sale	12,643
Loans, net	3,375,662	3,216,204
Derivatives	11,919	6,363
Accrued interest receivable	12,397	11,236
Financial liabilities:
Certificates of deposit	276,929	326,865
Demand and other deposits	3,559,655	3,556,902
FHLB advances	240,206	236,209
Repurchase agreements	945	539
Subordinated debentures	80,668	74,400
Derivatives	13,594	2,215
Accrued interest payable	1,718	1,524
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and due from banks	71,292	142,145
Interest-bearing deposits with banks	87,349	153,223
Securities available for sale	0	0
Securities held to maturity	0	0
Loans, net	0	0
Derivatives	0	0
Accrued interest receivable	0	0
Financial liabilities:
Certificates of deposit	0	0
Demand and other deposits	3,559,655	3,556,902
FHLB advances	0	0
Repurchase agreements	0	0
Subordinated debentures	0	0
Derivatives	0	0
Accrued interest payable	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities available for sale	642,897	680,886
Securities held to maturity	145,480	156,792
Loans held for sale	12,643
Loans, net	0	0
Derivatives	11,919	6,363
Accrued interest receivable	2,532	2,936
Financial liabilities:
Certificates of deposit	276,929	326,865
Demand and other deposits	0	0
FHLB advances	240,206	236,209
Repurchase agreements	945	539
Subordinated debentures	80,668	74,400
Derivatives	13,594	2,215
Accrued interest payable	1,718	1,524
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities available for sale	0	0
Securities held to maturity	0	0
Loans, net	3,375,662	3,216,204
Derivatives	0	0
Accrued interest receivable	9,865	8,300
Financial liabilities:
Certificates of deposit	0	0
Demand and other deposits	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Subordinated debentures	0	0
Derivatives	0	0
Accrued interest payable	$ 0	$ 0