FAIR VALUE - Summary of Estimated Fair Values and Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 87,004	$ 142,145
Interest-bearing deposits with banks	44,214	153,223
Securities available for sale	610,706	680,886
Securities held to maturity	141,503	156,792
Accrued interest receivable	11,697	11,236
Carrying Amount
Financial assets:
Cash and due from banks	87,004	142,145
Interest-bearing deposits with banks	44,214	153,223
Securities available for sale	610,706	680,886
Securities restricted	28,469	24,028
Securities held to maturity	139,729	160,163
Loans held for sale	12,643	0
Loans, net	3,476,159	3,244,393
Derivatives	19,227	6,363
Accrued interest receivable	11,697	11,236
Financial liabilities:
Certificates of deposit	269,777	329,491
Demand and other deposits	3,473,506	3,556,902
FHLB advances	337,000	240,433
Repurchase agreements	956	539
Subordinated debentures	78,885	78,781
Derivatives	21,950	2,215
Accrued interest payable	385	1,524
Fair Value
Financial assets:
Cash and due from banks	87,004	142,145
Interest-bearing deposits with banks	44,214	153,223
Securities available for sale	610,706	680,886
Securities held to maturity	141,503	156,792
Loans held for sale	12,643
Loans, net	3,456,345	3,216,204
Derivatives	19,227	6,363
Accrued interest receivable	11,697	11,236
Financial liabilities:
Certificates of deposit	270,291	326,865
Demand and other deposits	3,473,506	3,556,902
FHLB advances	337,881	236,209
Repurchase agreements	956	539
Subordinated debentures	82,633	74,400
Derivatives	21,950	2,215
Accrued interest payable	385	1,524
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and due from banks	87,004	142,145
Interest-bearing deposits with banks	44,214	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	3,473,506	3,556,902
FHLB advances	47,000	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	610,706	680,886
Securities held to maturity	141,503	156,792
Loans, net	0	0
Derivatives	19,227	6,363
Accrued interest receivable	2,524	2,936
Financial liabilities:
Certificates of deposit	270,291	326,865
Demand and other deposits	0	0
FHLB advances	290,881	236,209
Repurchase agreements	956	539
Subordinated debentures	82,633	74,400
Derivatives	21,950	2,215
Accrued interest payable	385	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 held for sale	12,643
Loans, net	3,456,345	3,216,204
Derivatives	0	0
Accrued interest receivable	9,173	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