INVESTMENT SECURITIES - Summary of Unrealized Losses - Held-to-Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities with losses under 12 months, Fair Value	$ 19,478	$ 31,802
Securities with losses under 12 months, Gross Unrealized Loss	117	362
Securities with losses over 12 months, Fair Value	12,090	8,645
Securities with losses over 12 months, Gross Unrealized Loss	451	323
Total, Fair Value	31,568	40,447
Total, Gross Unrealized Loss	568	685
Obligations of state and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Securities with losses under 12 months, Fair Value	6,340	8,054
Securities with losses under 12 months, Gross Unrealized Loss	22	39
Securities with losses over 12 months, Fair Value	0	0
Securities with losses over 12 months, Gross Unrealized Loss	0	0
Total, Fair Value	6,340	8,054
Total, Gross Unrealized Loss	22	39
GSE mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Securities with losses under 12 months, Fair Value	11,201	19,408
Securities with losses under 12 months, Gross Unrealized Loss	89	311
Securities with losses over 12 months, Fair Value	4,961	0
Securities with losses over 12 months, Gross Unrealized Loss	130	0
Total, Fair Value	16,162	19,408
Total, Gross Unrealized Loss	219	311
Collateralized mortgage obligations: residential
Schedule of Held-to-maturity Securities [Line Items]
Securities with losses under 12 months, Fair Value	0	0
Securities with losses under 12 months, Gross Unrealized Loss	0	0
Securities with losses over 12 months, Fair Value	7,129	8,645
Securities with losses over 12 months, Gross Unrealized Loss	321	323
Total, Fair Value	7,129	8,645
Total, Gross Unrealized Loss	321	323
Collateralized mortgage obligations: commercial
Schedule of Held-to-maturity Securities [Line Items]
Securities with losses under 12 months, Fair Value	1,937	4,340
Securities with losses under 12 months, Gross Unrealized Loss	6	12
Securities with losses over 12 months, Fair Value		0
Securities with losses over 12 months, Gross Unrealized Loss	0	0
Total, Fair Value	1,937	4,340
Total, Gross Unrealized Loss	$ 6	$ 12