FAIR VALUE - Summary of Estimated Fair Values and Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 68,773	$ 142,145
Interest-bearing deposits with banks	31,684	153,223
Securities available for sale	707,451	680,886
Securities held to maturity	147,633	156,792
Accrued interest receivable	13,057	11,236
Carrying Amount
Financial assets:
Cash and due from banks	68,773	142,145
Interest-bearing deposits with banks	31,684	153,223
Securities available for sale	707,451	680,886
Securities restricted	28,068	24,028
Securities held to maturity	149,512	160,163
Loans, net	3,359,320	3,244,393
Derivatives	7,663	6,363
Accrued interest receivable	13,057	11,236
Financial liabilities:
Certificates of deposit	280,709	329,491
Demand and other deposits	3,444,755	3,556,902
FHLB advances	330,217	240,433
Repurchase agreements	721	539
Subordinated debentures	78,815	78,781
Derivatives	5,772	2,215
Accrued interest payable	590	1,524
Fair Value
Financial assets:
Cash and due from banks	68,773	142,145
Interest-bearing deposits with banks	31,684	153,223
Securities available for sale	707,451	680,886
Securities held to maturity	147,633	156,792
Loans, net	3,346,699	3,216,204
Derivatives	7,663	6,363
Accrued interest receivable	13,057	11,236
Financial liabilities:
Certificates of deposit	279,236	326,865
Demand and other deposits	3,444,755	3,556,902
FHLB advances	327,499	236,209
Repurchase agreements	721	539
Subordinated debentures	78,058	74,400
Derivatives	5,772	2,215
Accrued interest payable	590	1,524
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and due from banks	68,773	142,145
Interest-bearing deposits with banks	31,684	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	3,444,755	3,556,902
FHLB advances	90,000	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	707,451	680,886
Securities held to maturity	147,633	156,792
Loans, net	0	0
Derivatives	7,663	6,363
Accrued interest receivable	2,980	2,936
Financial liabilities:
Certificates of deposit	279,236	326,865
Demand and other deposits	0	0
FHLB advances	237,499	236,209
Repurchase agreements	721	539
Subordinated debentures	78,058	74,400
Derivatives	5,772	2,215
Accrued interest payable	590	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	3,346,699	3,216,204
Derivatives	0	0
Accrued interest receivable	10,077	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