INVESTMENT SECURITIES, Investment Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2019 USD ($) Position	Dec. 31, 2018 USD ($) Position
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	6	169
12 months or longer | Position	176	384
Total | Position	182	553
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 4,551	$ 576,527
12 months or longer	402,781	1,584,618
Total	407,332	2,161,145
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	6	1,156
12 months or longer	2,715	25,412
Total	$ 2,721	$ 26,568
Equity and Other Securities, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position		1
12 months or longer | Position		0
Total | Position		1
Equity and Other Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 82
12 months or longer		0
Total		82
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months		19
12 months or longer		0
Total		$ 19
U.S. Treasury and Agency Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	0	7
12 months or longer | Position	19	64
Total | Position	19	71
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 473,082
12 months or longer	188,692	1,213,276
Total	188,692	1,686,358
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	0	682
12 months or longer	428	14,229
Total	$ 428	$ 14,911
Obligations of State and Political Subdivisions [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	0	118
12 months or longer | Position	1	97
Total | Position	1	215
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 55,671
12 months or longer	516	51,753
Total	516	107,424
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	0	216
12 months or longer	0	833
Total	$ 0	$ 1,049
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	6	43
12 months or longer | Position	142	181
Total | Position	148	224
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 4,551	$ 47,708
12 months or longer	192,786	253,931
Total	197,337	301,639
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	6	258
12 months or longer	2,215	9,025
Total	$ 2,221	$ 9,283
Corporate Debt Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	0	0
12 months or longer | Position	1	1
Total | Position	1	1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 0
12 months or longer	2,554	2,546
Total	2,554	2,546
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	0	0
12 months or longer	4	42
Total	$ 4	$ 42
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	0	1
12 months or longer | Position	13	41
Total | Position	13	42
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 66
12 months or longer	18,233	63,112
Total	18,233	63,178
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	0	0
12 months or longer	68	1,283
Total	$ 68	$ 1,283
Equity Securities, at Fair Value [Member]
Equity and Other Securities, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position		1
12 months or longer | Position		0
Total | Position		1
Equity and Other Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 82
12 months or longer		0
Total		82
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months		19
12 months or longer		0
Total		$ 19