SECURITIES (Schedule of Securities) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Schedule of Securities [Line Items]
Securities—trading, Amortized Cost	$ 27,203,000	$ 27,203,000
Securities—trading	25,097,000	24,980,000
Available-for-sale Securities, Amortized Cost	3,249,579,000	2,256,189,000
Available-for-sale Securities, Gross Unrealized Gains	55,421,000	68,543,000
Available-for-sale Securities, Gross Unrealized Losses	(29,021,000)	(2,139,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	3,275,979,000	2,322,593,000
Held-to-maturity Securities, Amortized Cost	455,366,000	421,807,000
Held-to-maturity Securities, Gross Unrealized Gains	25,421,000	26,980,000
Held-to-maturity Securities, Gross Unrealized Losses	810,000	106,000
Securities—held-to-maturity	479,977,000	448,681,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	110,000	(94,000)
debt securities, held-to-maturity, accrued interest receivable	3,000,000.0
Debt Securities, Available-for-Sale, Accrued Interest Receivable	8,800,000	6,900,000
Trading Securities, Unrealized Holding Gain	117,000
U.S. Government and agency obligations
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	94,847,000	141,668,000
Available-for-sale Securities, Gross Unrealized Gains	1,039,000	1,002,000
Available-for-sale Securities, Gross Unrealized Losses	(784,000)	(935,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	95,102,000	141,735,000
Held-to-maturity Securities, Amortized Cost	318,000	340,000
Held-to-maturity Securities, Gross Unrealized Gains	3,000	7,000
Held-to-maturity Securities, Gross Unrealized Losses	0	0
Securities—held-to-maturity	321,000	347,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0	$ 0	$ 0	$ 0
Municipal bonds
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	311,533,000	283,997,000
Available-for-sale Securities, Gross Unrealized Gains	17,180,000	19,523,000
Available-for-sale Securities, Gross Unrealized Losses	(47,000)	(2,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	328,666,000	303,518,000
Held-to-maturity Securities, Amortized Cost	395,683,000	370,998,000
Held-to-maturity Securities, Gross Unrealized Gains	22,945,000	24,130,000
Held-to-maturity Securities, Gross Unrealized Losses	803,000	94,000
Securities—held-to-maturity	417,825,000	395,034,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	64,000	59,000	61,000	61,000	0
Corporate bonds
Schedule of Securities [Line Items]
Securities—trading, Amortized Cost	27,203,000	27,203,000
Securities—trading	25,097,000	24,980,000
Available-for-sale Securities, Amortized Cost	268,387,000	219,086,000
Available-for-sale Securities, Gross Unrealized Gains	3,703,000	2,762,000
Available-for-sale Securities, Gross Unrealized Losses	(14,000)	(79,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	272,076,000	221,769,000
Held-to-maturity Securities, Amortized Cost	3,157,000	3,222,000
Held-to-maturity Securities, Gross Unrealized Gains	0	0
Held-to-maturity Securities, Gross Unrealized Losses	7,000	12,000
Securities—held-to-maturity	3,150,000	3,210,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	46,000	35,000	41,000	37,000	0
Mortgage-backed or related securities
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	2,496,181,000	1,602,033,000
Available-for-sale Securities, Gross Unrealized Gains	33,492,000	45,179,000
Available-for-sale Securities, Gross Unrealized Losses	(28,176,000)	(1,060,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	2,501,497,000	1,646,152,000
Held-to-maturity Securities, Amortized Cost	56,208,000	47,247,000
Held-to-maturity Securities, Gross Unrealized Gains	2,473,000	2,843,000
Held-to-maturity Securities, Gross Unrealized Losses	0	0
Securities—held-to-maturity	58,681,000	50,090,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	0	$ 0	$ 0	$ 0
Asset-backed securities
Schedule of Securities [Line Items]
Available-for-sale Securities, Amortized Cost	78,631,000	9,405,000
Available-for-sale Securities, Gross Unrealized Gains	7,000	77,000
Available-for-sale Securities, Gross Unrealized Losses	0	(63,000)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0	0
Securities—available-for-sale	$ 78,638,000	$ 9,419,000