SECURITIES - Investment Securities Available for Sale in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale securities in a continuous unrealized loss position, fair value [Abstract]
Less than 12 months	$ 123,007	$ 259,567
12 months or longer	131,436	225
Total	254,443	259,792
Available-for-sale securities in a continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	1,199	7,804
12 months or longer	4,171	1
Total	5,370	7,805
Obligations of U.S. Government and U.S. Government sponsored enterprises
Available-for-sale securities in a continuous unrealized loss position, fair value [Abstract]
Less than 12 months	14,982
12 months or longer	0
Total	14,982
Available-for-sale securities in a continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	21
12 months or longer	0
Total	21
Mortgage-backed securities, residential
Available-for-sale securities in a continuous unrealized loss position, fair value [Abstract]
Less than 12 months	83,562	233,843
12 months or longer	131,165	0
Total	214,727	233,843
Available-for-sale securities in a continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	1,013	7,492
12 months or longer	4,153	0
Total	5,166	7,492
Obligations of states and political subdivisions
Available-for-sale securities in a continuous unrealized loss position, fair value [Abstract]
Less than 12 months	20,526	25,724
12 months or longer	271	0
Total	20,797	25,724
Available-for-sale securities in a continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	133	312
12 months or longer	18	0
Total	151	312
SBA loan pools
Available-for-sale securities in a continuous unrealized loss position, fair value [Abstract]
Less than 12 months	3,937	0
12 months or longer	0	225
Total	3,937	225
Available-for-sale securities in a continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	32	0
12 months or longer	0	1
Total	$ 32	$ 1