SECURITIES (Schedule of Securities) (Details) - USD ($)	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Schedule of Securities [Line Items]
Debt Securities, Trading, Amortized Cost	$ 27,203,000		$ 27,203,000
Securities—trading	26,875,000		24,980,000
Debt Securities, Available-for-sale, Amortized Cost, Total	3,443,516,000		2,256,189,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	45,393,000		68,543,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	42,334,000		2,139,000
Debt Securities, Available-for-sale	3,446,575,000		2,322,593,000
Held-to-maturity Securities, Amortized Cost	447,812,000		421,807,000
Held-to-maturity Securities, Gross Unrealized Gains	20,390,000		26,980,000
Held-to-maturity Securities, Gross Unrealized Losses	2,200,000		106,000
Securities—held-to-maturity	466,002,000		448,681,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	104,000		(94,000)
debt securities, held-to-maturity, accrued interest receivable	2,700,000		3,000,000
Debt Securities, Available-for-Sale, Accrued Interest Receivable	9,300,000		6,900,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0		0
U.S. Government and agency obligations
Schedule of Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost, Total	180,585,000		141,668,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,067,000		1,002,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	600,000		935,000
Debt Securities, Available-for-sale	181,052,000		141,735,000
Held-to-maturity Securities, Amortized Cost	317,000		340,000
Held-to-maturity Securities, Gross Unrealized Gains	6,000		7,000
Held-to-maturity Securities, Gross Unrealized Losses	0		0
Securities—held-to-maturity	323,000		347,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	$ 0	0	$ 0	$ 0	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0		0
Municipal bonds
Schedule of Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost, Total	296,784,000		283,997,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	14,395,000		19,523,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	788,000		2,000
Debt Securities, Available-for-sale	310,391,000		303,518,000
Held-to-maturity Securities, Amortized Cost	391,583,000		370,998,000
Held-to-maturity Securities, Gross Unrealized Gains	18,716,000		24,130,000
Held-to-maturity Securities, Gross Unrealized Losses	2,188,000		94,000
Securities—held-to-maturity	408,111,000		395,034,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	63,000	64,000	59,000	60,000	61,000	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0		0
Corporate bonds
Schedule of Securities [Line Items]
Debt Securities, Trading, Amortized Cost	27,203,000		27,203,000
Securities—trading	26,875,000		24,980,000
Debt Securities, Available-for-sale, Amortized Cost, Total	160,404,000		219,086,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	3,903,000		2,762,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	63,000		79,000
Debt Securities, Available-for-sale	164,244,000		221,769,000
Held-to-maturity Securities, Amortized Cost	3,124,000		3,222,000
Held-to-maturity Securities, Gross Unrealized Gains	0		0
Held-to-maturity Securities, Gross Unrealized Losses	2,000		12,000
Securities—held-to-maturity	3,122,000		3,210,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	41,000	46,000	35,000	42,000	41,000	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0		0
Mortgage-backed or related securities
Schedule of Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost, Total	2,599,229,000		1,602,033,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	25,918,000		45,179,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	40,883,000		1,060,000
Debt Securities, Available-for-sale	2,584,264,000		1,646,152,000
Held-to-maturity Securities, Amortized Cost	52,788,000		47,247,000
Held-to-maturity Securities, Gross Unrealized Gains	1,668,000		2,843,000
Held-to-maturity Securities, Gross Unrealized Losses	10,000		0
Securities—held-to-maturity	54,446,000		50,090,000
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0	$ 0	0	$ 0	$ 0	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	0		0
Asset-backed securities
Schedule of Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost, Total	206,514,000		9,405,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	110,000		77,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0		63,000
Debt Securities, Available-for-sale	206,624,000		9,419,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	$ 0		$ 0