SECURITIES (Schedule of Securities) (Details) - USD ($)	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Securities [Line Items]
Securities—trading, Amortized Cost	$ 27,203,000		$ 27,203,000
Securities—trading	21,040,000		25,636,000
Available-for-sale Securities, Amortized Cost	1,544,513,000		1,529,946,000
Available-for-sale Securities, Gross Unrealized Gains	66,058,000		25,858,000
Available-for-sale Securities, Gross Unrealized Losses	(2,347,000)		(4,247,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	1,608,224,000		1,551,557,000
Held-to-maturity Securities, Amortized Cost	437,944,000		236,094,000
Held-to-maturity Securities, Gross Unrealized Gains	13,607,000		4,658,000
Held-to-maturity Securities, Gross Unrealized Losses	2,314,000		2,947,000
Securities—held-to-maturity	449,237,000		237,805,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	98,000	$ 0	0
U.S. Government and agency obligations [Member]
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	82,197,000		90,468,000
Available-for-sale Securities, Gross Unrealized Gains	520,000		286,000
Available-for-sale Securities, Gross Unrealized Losses	(954,000)		(1,156,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	81,763,000		89,598,000
Held-to-maturity Securities, Amortized Cost	373,000		385,000
Held-to-maturity Securities, Gross Unrealized Gains	8,000		4,000
Held-to-maturity Securities, Gross Unrealized Losses	0		0
Securities—held-to-maturity	381,000		389,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0	0
Municipal bonds
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	171,486,000		101,927,000
Available-for-sale Securities, Gross Unrealized Gains	9,726,000		5,233,000
Available-for-sale Securities, Gross Unrealized Losses	(173,000)		(3,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	181,039,000		107,157,000
Held-to-maturity Securities, Amortized Cost	380,483,000		177,208,000
Held-to-maturity Securities, Gross Unrealized Gains	10,830,000		3,733,000
Held-to-maturity Securities, Gross Unrealized Losses	2,292,000		2,213,000
Securities—held-to-maturity	389,021,000		178,728,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	61,000	0	0
Corporate bonds
Schedule of Securities [Line Items]
Securities—trading, Amortized Cost	27,203,000		27,203,000
Securities—trading	21,040,000		25,636,000
Available-for-sale Securities, Amortized Cost	30,094,000		4,357,000
Available-for-sale Securities, Gross Unrealized Gains	1,101,000		14,000
Available-for-sale Securities, Gross Unrealized Losses	(209,000)		(6,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	30,986,000		4,365,000
Held-to-maturity Securities, Amortized Cost	3,325,000		3,353,000
Held-to-maturity Securities, Gross Unrealized Gains	0		0
Held-to-maturity Securities, Gross Unrealized Losses	10,000		11,000
Securities—held-to-maturity	3,315,000		3,342,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	37,000	0	0
Mortgage-backed or related securities [Member]
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	1,252,606,000		1,324,999,000
Available-for-sale Securities, Gross Unrealized Gains	54,711,000		20,325,000
Available-for-sale Securities, Gross Unrealized Losses	(518,000)		(3,013,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	1,306,799,000		1,342,311,000
Held-to-maturity Securities, Amortized Cost	53,763,000		55,148,000
Held-to-maturity Securities, Gross Unrealized Gains	2,769,000		921,000
Held-to-maturity Securities, Gross Unrealized Losses	12,000		723,000
Securities—held-to-maturity	56,520,000		55,346,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	$ 0	0
Asset-backed Securities [Member]
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	8,130,000		8,195,000
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	(493,000)		(69,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0
Securities—available-for-sale	$ 7,637,000		$ 8,126,000