INVESTMENT SECURITIES - Summary of Unrealized Loss Positions (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Investments in an unrealized loss position
Held-to-maturity Securities, Fair Value	$ 0	$ 0
Amount of pretax loss if securities in an unrealized loss position are sold	2,500,000
Available-for sale Securities, Unrealized Loss Position
Less than 12 months, fair value	88,519,000
Less than 12 months, unrealized loss	(884,000)
12 months or more, fair value	61,917,000
12 months or more, unrealized loss	(1,612,000)
Available-for-sale and Held-to-Maturity Securities, Unrealized Loss Position
Less than 12 months, fair value		104,750,000
Less than 12 months, unrealized loss		(3,488,000)
12 months or more, fair value		13,919,000
12 months or more, unrealized loss		(322,000)
Available-for-sale Securities
Sales of investment securities	53,198,000	55,191,000	$ 12,912,000
Gains on the sale of investments	1,100,000	1,100,000	125,000
Losses on the sale of investments	372,000	2,000	0
Held-to-maturity Securities
Sales of investment securities	$ 0	$ 0	421,000
Gains on the sale of held-to-maturity securities			$ 5,000
U. S. Agency securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security	45	16
Available-for sale Securities, Unrealized Loss Position
Less than 12 months, fair value	$ 61,834,000	$ 28,814,000
Less than 12 months, unrealized loss	(659,000)	(425,000)
12 months or more, fair value	7,709,000	0
12 months or more, unrealized loss	$ (182,000)	$ 0
U.S. Sponsored Mortgage-backed securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security	39	29
Available-for sale Securities, Unrealized Loss Position
Less than 12 months, fair value	$ 16,825,000	$ 33,209,000
Less than 12 months, unrealized loss	(159,000)	(1,040,000)
12 months or more, fair value	37,427,000	13,919,000
12 months or more, unrealized loss	$ (1,105,000)	$ (322,000)
Municipal securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security	47
Number of investments in an unrealized loss position, HTM | security		86
Available-for sale Securities, Unrealized Loss Position
Less than 12 months, fair value	$ 8,826,000
Less than 12 months, unrealized loss	(48,000)
12 months or more, fair value	16,781,000
12 months or more, unrealized loss	$ (325,000)
Held-to-maturity Securities, Unrealized Loss Position
Less than 12 months, fair value		$ 42,727,000
Less than 12 months, unrealized loss		(2,023,000)
12 months or more, fair value		0
12 months or more, unrealized loss		$ 0
Equity and other securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security	2
Available-for sale Securities, Unrealized Loss Position
Less than 12 months, fair value	$ 1,034,000
Less than 12 months, unrealized loss	(18,000)
12 months or more, fair value	0
12 months or more, unrealized loss	$ 0