SECURITIES (Debt securities available for sale) (Details) $ in Thousands	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 4,889,934	$ 3,226,422
Unrealized Losses, Less than 12 months	$ (279,331)	$ (57,123)
Count, Less than 12 months | security	878	242
Fair Value, 12 months or longer	$ 1,106,545	$ 815,822
Unrealized Losses, 12 months or longer	$ (114,111)	$ (27,110)
Count, 12 months or longer | security	130	86
Fair Value, Total	$ 5,996,479	$ 4,042,244
Unrealized Losses, Total	$ (393,442)	$ (84,233)
Count, Total | security	1,008	328
U.S. agencies
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 66,819	$ 100,839
Unrealized Losses, Less than 12 months	$ (1,701)	$ (812)
Count, Less than 12 months | security	8	2
Fair Value, 12 months or longer	$ 17,475	$ 0
Unrealized Losses, 12 months or longer	$ (2,041)	$ 0
Count, 12 months or longer | security	1	0
Fair Value, Total	$ 84,294	$ 100,839
Unrealized Losses, Total	$ (3,742)	$ (812)
Count, Total | security	9	2
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,321,666	$ 596,866
Unrealized Losses, Less than 12 months	$ (124,133)	$ (10,115)
Count, Less than 12 months | security	305	113
Fair Value, 12 months or longer	$ 297,576	$ 236,329
Unrealized Losses, 12 months or longer	$ (46,393)	$ (6,501)
Count, 12 months or longer | security	69	49
Fair Value, Total	$ 1,619,242	$ 833,195
Unrealized Losses, Total	$ (170,526)	$ (16,616)
Count, Total | security	374	162
Mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,439,275	$ 1,383,808
Unrealized Losses, Less than 12 months	$ (82,994)	$ (33,291)
Count, Less than 12 months | security	311	83
Fair Value, 12 months or longer	$ 617,833	$ 474,724
Unrealized Losses, 12 months or longer	$ (55,010)	$ (17,891)
Count, 12 months or longer | security	40	19
Fair Value, Total	$ 2,057,108	$ 1,858,532
Unrealized Losses, Total	$ (138,004)	$ (51,182)
Count, Total | security	351	102
Mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,288,511	$ 929,515
Unrealized Losses, Less than 12 months	$ (58,783)	$ (10,870)
Count, Less than 12 months | security	154	27
Fair Value, 12 months or longer	$ 93,072	$ 23,821
Unrealized Losses, 12 months or longer	$ (3,369)	$ (159)
Count, 12 months or longer | security	7	5
Fair Value, Total	$ 1,381,583	$ 953,336
Unrealized Losses, Total	$ (62,152)	$ (11,029)
Count, Total | security	161	32
Commercial mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 47,449	$ 26,999
Unrealized Losses, Less than 12 months	$ (2,204)	$ (689)
Count, Less than 12 months | security	18	8
Fair Value, 12 months or longer	$ 57,260	$ 53,025
Unrealized Losses, 12 months or longer	$ (6,911)	$ (2,225)
Count, 12 months or longer | security	7	5
Fair Value, Total	$ 104,709	$ 80,024
Unrealized Losses, Total	$ (9,115)	$ (2,914)
Count, Total | security	25	13
Commercial mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 621,766	$ 74,450
Unrealized Losses, Less than 12 months	$ (5,526)	$ (145)
Count, Less than 12 months | security	61	3
Fair Value, 12 months or longer	$ 14,030	$ 14,124
Unrealized Losses, 12 months or longer	$ (214)	$ (218)
Count, 12 months or longer | security	2	2
Fair Value, Total	$ 635,796	$ 88,574
Unrealized Losses, Total	$ (5,740)	$ (363)
Count, Total | security	63	5
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 98,835	$ 113,945
Unrealized Losses, Less than 12 months	$ (3,882)	$ (1,201)
Count, Less than 12 months | security	18	6
Fair Value, 12 months or longer	$ 9,299	$ 13,799
Unrealized Losses, 12 months or longer	$ (173)	$ (116)
Count, 12 months or longer | security	4	6
Fair Value, Total	$ 108,134	$ 127,744
Unrealized Losses, Total	$ (4,055)	$ (1,317)
Count, Total | security	22	12
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 5,613
Unrealized Losses, Less than 12 months	$ (108)
Count, Less than 12 months | security	3
Fair Value, 12 months or longer	$ 0
Unrealized Losses, 12 months or longer	$ 0
Count, 12 months or longer | security	0
Fair Value, Total	$ 5,613
Unrealized Losses, Total	$ (108)
Count, Total | security	3