INVESTMENT SECURITIES, Investment Securities in a Continuous Unrealized Loss Position (Details)	Mar. 31, 2020 USD ($) Position	Dec. 31, 2019 USD ($) Position
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	11	88
12 months or longer | Position	5	62
Total | Position	16	150
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 5,106,000	$ 710,602,000
12 months or longer	331,000	83,378,000
Total	5,437,000	793,980,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	16,000	8,351,000
12 months or longer	0	789,000
Total	$ 16,000	$ 9,140,000
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	$ 73,000
12 months or longer	0
Total	73,000
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	28,000
12 months or longer	0
Total	28,000
Available-for-sale, allowance for credit losses	$ 0
U.S. Treasury and Agency Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position		12
12 months or longer | Position		5
Total | Position		17
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 592,678,000
12 months or longer		25,998,000
Total		618,676,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months		7,970,000
12 months or longer		5,000
Total		$ 7,975,000
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	21
12 months or longer | Position	0	0
Total | Position	9	21
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 1,444,000	$ 22,716,000
12 months or longer	0	0
Total	1,444,000	22,716,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	2,000	26,000
12 months or longer	0	0
Total	$ 2,000	$ 26,000
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	1	50
12 months or longer | Position	3	52
Total | Position	4	102
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 1,154,000	$ 89,237,000
12 months or longer	304,000	52,975,000
Total	1,458,000	142,212,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	10,000	341,000
12 months or longer	0	766,000
Total	$ 10,000	$ 1,107,000
Corporate Debt Securities [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	1
12 months or longer | Position	0
Total | Position	1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 2,508,000
12 months or longer	0
Total	2,508,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	4,000
12 months or longer	0
Total	$ 4,000
Corporate Debt Securities [Member] | A- or Better [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Total | Position	1
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months | Position	0	5
12 months or longer | Position	2	5
Total | Position	2	10
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 5,971,000
12 months or longer	27,000	4,405,000
Total	27,000	10,376,000
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Less than 12 months	0	14,000
12 months or longer	0	18,000
Total	$ 0	$ 32,000
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	$ 73,000
12 months or longer	0
Total	73,000
Equity and Other Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	28,000
12 months or longer	0
Total	$ 28,000