SECURITIES (Debt securities available for sale) (Details) $ in Thousands	Jun. 30, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 5,108,015	$ 3,226,422
Unrealized Losses, Less than 12 months	$ (463,817)	$ (57,123)
Count, Less than 12 months | security	513	242
Fair Value, 12 months or longer	$ 1,196,846	$ 815,822
Unrealized Losses, 12 months or longer	$ (188,984)	$ (27,110)
Count, 12 months or longer | security	144	86
Fair Value, Total	$ 6,304,861	$ 4,042,244
Unrealized Losses, Total	$ (652,801)	$ (84,233)
Count, Total | security	657	328
U.S. agencies
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 28,629	$ 100,839
Unrealized Losses, Less than 12 months	$ (1,678)	$ (812)
Count, Less than 12 months | security	6	2
Fair Value, 12 months or longer	$ 16,587	$ 0
Unrealized Losses, 12 months or longer	$ (2,943)	$ 0
Count, 12 months or longer | security	1	0
Fair Value, Total	$ 45,216	$ 100,839
Unrealized Losses, Total	$ (4,621)	$ (812)
Count, Total | security	7	2
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,381,161	$ 596,866
Unrealized Losses, Less than 12 months	$ (249,231)	$ (10,115)
Count, Less than 12 months | security	255	113
Fair Value, 12 months or longer	$ 270,570	$ 236,329
Unrealized Losses, 12 months or longer	$ (78,583)	$ (6,501)
Count, 12 months or longer | security	73	49
Fair Value, Total	$ 1,651,731	$ 833,195
Unrealized Losses, Total	$ (327,814)	$ (16,616)
Count, Total | security	328	162
Mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,205,936	$ 1,383,808
Unrealized Losses, Less than 12 months	$ (93,294)	$ (33,291)
Count, Less than 12 months | security	153	83
Fair Value, 12 months or longer	$ 749,833	$ 474,724
Unrealized Losses, 12 months or longer	$ (94,540)	$ (17,891)
Count, 12 months or longer | security	52	19
Fair Value, Total	$ 1,955,769	$ 1,858,532
Unrealized Losses, Total	$ (187,834)	$ (51,182)
Count, Total | security	205	102
Mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,623,955	$ 929,515
Unrealized Losses, Less than 12 months	$ (94,481)	$ (10,870)
Count, Less than 12 months | security	43	27
Fair Value, 12 months or longer	$ 87,366	$ 23,821
Unrealized Losses, 12 months or longer	$ (4,234)	$ (159)
Count, 12 months or longer | security	7	5
Fair Value, Total	$ 1,711,321	$ 953,336
Unrealized Losses, Total	$ (98,715)	$ (11,029)
Count, Total | security	50	32
Commercial mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 51,811	$ 26,999
Unrealized Losses, Less than 12 months	$ (3,699)	$ (689)
Count, Less than 12 months | security	20	8
Fair Value, 12 months or longer	$ 46,041	$ 53,025
Unrealized Losses, 12 months or longer	$ (7,400)	$ (2,225)
Count, 12 months or longer | security	6	5
Fair Value, Total	$ 97,852	$ 80,024
Unrealized Losses, Total	$ (11,099)	$ (2,914)
Count, Total | security	26	13
Commercial mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 607,320	$ 74,450
Unrealized Losses, Less than 12 months	$ (14,325)	$ (145)
Count, Less than 12 months | security	19	3
Fair Value, 12 months or longer	$ 12,015	$ 14,124
Unrealized Losses, 12 months or longer	$ (177)	$ (218)
Count, 12 months or longer | security	2	2
Fair Value, Total	$ 619,335	$ 88,574
Unrealized Losses, Total	$ (14,502)	$ (363)
Count, Total | security	21	5
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 200,036	$ 113,945
Unrealized Losses, Less than 12 months	$ (6,560)	$ (1,201)
Count, Less than 12 months | security	10	6
Fair Value, 12 months or longer	$ 14,434	$ 13,799
Unrealized Losses, 12 months or longer	$ (1,107)	$ (116)
Count, 12 months or longer | security	3	6
Fair Value, Total	$ 214,470	$ 127,744
Unrealized Losses, Total	$ (7,667)	$ (1,317)
Count, Total | security	13	12
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 8,169
Unrealized Losses, Less than 12 months	$ (548)
Count, Less than 12 months | security	6
Fair Value, 12 months or longer	$ 0
Unrealized Losses, 12 months or longer	$ 0
Count, 12 months or longer | security	0
Fair Value, Total	$ 8,169
Unrealized Losses, Total	$ (548)
Count, Total | security	6
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 998
Unrealized Losses, Less than 12 months	$ (1)
Count, Less than 12 months | security	1
Fair Value, 12 months or longer	$ 0
Unrealized Losses, 12 months or longer	$ 0
Count, 12 months or longer | security	0
Fair Value, Total	$ 998
Unrealized Losses, Total	$ (1)
Count, Total | security	1