INVESTMENT SECURITIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Investments, Debt and Equity Securities [Abstract]
Number of private-label collateralized mortgage obligations | security	1
Combined balance of private-label collateralized mortgage obligations	$ 7,000	$ 18,000
Number of securities in unrealized loss positions | security	84
Unrealized losses as a percentage of individual securities, amortized cost basis	2.05%
Unrealized losses as percentage of Company's total amortized cost basis	1.51%
Number of securities in an unrealized loss position for more than 12 months | security	46
Amortized cost basis of securities in a continuous loss position	$ 175,500,000
Unrealized loss on securities in a continuous loss position	5,000,000
Impairment related to credit quality	$ 0
Number of available-for-sale securities sold | security	16		22
Number Of Held to Maturity Securities Sold | security	1
Held-to-maturity Securities, Sold Security, Realized Gain (Loss)	$ 7,000
Number of available-for-sale securities sold with gains | security	13	2	12
Available-for-sale securities, total gains	$ 449,000	$ 20,000	$ 1,400,000
Number of available-for-sale securities sold with loss | security	3		10
Available-for-sale securities sold at a loss	$ 109,000		$ 135,000
Available-for-sale Securities, Gross Realized Gain (Loss)	340,000		$ 1,200,000
Securities pledged as collateral for public funding	$ 177,900,000	$ 293,400,000