INVESTMENT SECURITIES, Investment Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2017 USD ($) Position	Dec. 31, 2016 USD ($) Position
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	155	268
12 months or longer | Position	30	17
Total | Position	185	285
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 413,043	$ 637,887
12 months or longer	36,148	21,790
Total	449,191	659,677
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	1,601	4,840
12 months or longer	1,270	830
Total	$ 2,871	$ 5,670
U.S. Treasury and Agency Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	24	13
12 months or longer | Position	0	0
Total | Position	24	13
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 201,051	$ 449,242
12 months or longer	0	0
Total	201,051	449,242
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	382	2,118
12 months or longer	0	0
Total	$ 382	$ 2,118
Obligations of State and Political Subdivisions [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	9	197
12 months or longer | Position	1	0
Total | Position	10	197
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 4,386	$ 102,106
12 months or longer	365	0
Total	4,751	102,106
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	21	1,054
12 months or longer	5	0
Total	$ 26	$ 1,054
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	94	57
12 months or longer | Position	27	15
Total | Position	121	72
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 142,538	$ 83,862
12 months or longer	35,781	21,788
Total	178,319	105,650
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	1,049	1,637
12 months or longer	1,265	830
Total	$ 2,314	$ 2,467
Corporate Debt Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	1	1
12 months or longer | Position	0	0
Total | Position	1	1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 2,662	$ 2,677
12 months or longer	0	0
Total	2,662	2,677
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	1	31
12 months or longer	0	0
Total	$ 1	$ 31
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	27	0
12 months or longer | Position	2	2
Total | Position	29	2
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 62,406	$ 0
12 months or longer	2	2
Total	62,408	2
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	148	0
12 months or longer	0	0
Total	$ 148	$ 0