SECURITIES - Contractual Maturities of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale, Amortized Cost
Due in one year or less	$ 1,789
Due after one year through five years	0
Due after five years through ten years	4,236
Due after ten years	6,436
Total	12,461
Total Amortized Cost	715,507	$ 275,734
Available-for-sale, Fair Value
Due in one year or less	1,794
Due after one year through five years	0
Due after five years through ten years	4,236
Due after ten years	6,390
Total	12,420
Total Fair Value	705,539	274,619
Held-to-maturity, Amortized Cost
Total Amortized Cost	13,275	35,505
Held-to-maturity, Fair Value
Total Fair Value	13,146	34,844
Mortgage-backed securities and collateralized mortgage obligations
Available-for-sale, Amortized Cost
Amortized cost	587,598
Available-for-sale, Fair Value
Fair value	578,789
Held-to-maturity, Amortized Cost
Debt maturities without single maturity date	13,275
Held-to-maturity, Fair Value
Debt maturities without single maturity date	13,146
SBA guaranteed securities
Available-for-sale, Amortized Cost
Amortized cost	104,111
Total Amortized Cost	104,111
Available-for-sale, Fair Value
Fair value	103,292
Total Fair Value	103,292
CRA qualified investment fund
Available-for-sale, Amortized Cost
Amortized cost	11,337
Total Amortized Cost	11,337	11,183
Available-for-sale, Fair Value
Fair value	11,038
Total Fair Value	$ 11,038	$ 10,913