INVESTMENT SECURITIES, Investment Securities in a Continuous Unrealized Loss Position (Details)	Dec. 31, 2019 USD ($) Position	Dec. 31, 2018 USD ($) Position
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	88	169
12 months or longer | Position	62	384
Total | Position	150	553
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 710,602,000	$ 576,527,000
12 months or longer	83,378,000	1,584,618,000
Total	793,980,000	2,161,145,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	8,351,000	1,156,000
12 months or longer	789,000	25,412,000
Total	$ 9,140,000	$ 26,568,000
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		$ 82,000
12 months or longer		0
Total		82,000
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months		19,000
12 months or longer		0
Total		$ 19,000
U.S. Treasury and Agency Securities [Member]
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	12	7
12 months or longer | Position	5	64
Total | Position	17	71
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 592,678,000	$ 473,082,000
12 months or longer	25,998,000	1,213,276,000
Total	618,676,000	1,686,358,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	7,970,000	682,000
12 months or longer	5,000	14,229,000
Total	$ 7,975,000	$ 14,911,000
Obligations of State and Political Subdivisions [Member]
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	21	118
12 months or longer | Position	0	97
Total | Position	21	215
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 22,716,000	$ 55,671,000
12 months or longer	0	51,753,000
Total	22,716,000	107,424,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	26,000	216,000
12 months or longer	0	833,000
Total	$ 26,000	$ 1,049,000
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	50	43
12 months or longer | Position	52	181
Total | Position	102	224
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 89,237,000	$ 47,708,000
12 months or longer	52,975,000	253,931,000
Total	142,212,000	301,639,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	341,000	258,000
12 months or longer	766,000	9,025,000
Total	$ 1,107,000	$ 9,283,000
Corporate Debt Securities [Member]
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position		0
12 months or longer | Position		1
Total | Position		1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 0
12 months or longer		2,546,000
Total		2,546,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months		0
12 months or longer		42,000
Total		$ 42,000
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	5	1
12 months or longer | Position	5	41
Total | Position	10	42
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 5,971,000	$ 66,000
12 months or longer	4,405,000	63,112,000
Total	10,376,000	63,178,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	14,000	0
12 months or longer	18,000	1,283,000
Total	$ 32,000	$ 1,283,000
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		$ 82,000
12 months or longer		0
Total		82,000
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months		19,000
12 months or longer		0
Total		$ 19,000