SECURITIES (Debt securities available for sale) (Details) $ in Thousands	Mar. 31, 2024 USD ($) security investmentCategory	Dec. 31, 2023 USD ($) security
Fair Value
Less than 12 months	$ 601,458	$ 629,647
12 months or longer	3,608,754	3,770,658
Total	4,210,212	4,400,305
Unrealized Losses
Less than 12 months	(35,756)	(34,481)
12 months or longer	(432,381)	(419,373)
Total	$ (468,137)	$ (453,854)
Count
Less than 12 months | security	22	21
12 months or longer | security	405	406
Total | security	427	427
Number of investment categories | investmentCategory	2
U.S. treasuries
Fair Value
Less than 12 months	$ 2,975	$ 2,985
12 months or longer	29,247	26,138
Total	32,222	29,123
Unrealized Losses
Less than 12 months	(20)	(12)
12 months or longer	(239)	(329)
Total	$ (259)	$ (341)
Count
Less than 12 months | security	1	1
12 months or longer | security	4	3
Total | security	5	4
U.S. agencies
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	13,892	14,530
Total	13,892	14,530
Unrealized Losses
Less than 12 months	0	0
12 months or longer	(192)	(194)
Total	$ (192)	$ (194)
Count
Less than 12 months | security	0	0
12 months or longer | security	4	4
Total | security	4	4
Obligations of states and political subdivisions
Fair Value
Less than 12 months	$ 1,689	$ 1,440
12 months or longer	721,778	736,653
Total	723,467	738,093
Unrealized Losses
Less than 12 months	(16)	(65)
12 months or longer	(109,328)	(98,469)
Total	$ (109,344)	$ (98,534)
Count
Less than 12 months | security	3	1
12 months or longer | security	148	150
Total | security	151	151
Mortgage-backed securities - agency
Fair Value
Less than 12 months	$ 0	$ 194
12 months or longer	1,358,884	1,392,769
Total	1,358,884	1,392,963
Unrealized Losses
Less than 12 months	0	(2)
12 months or longer	(231,254)	(226,791)
Total	$ (231,254)	$ (226,793)
Count
Less than 12 months | security	0	2
12 months or longer | security	166	166
Total | security	166	168
Mortgage-backed securities - non-agency
Fair Value
Less than 12 months	$ 395,105	$ 415,934
12 months or longer	880,665	902,291
Total	1,275,770	1,318,225
Unrealized Losses
Less than 12 months	(22,829)	(24,568)
12 months or longer	(62,396)	(63,081)
Total	$ (85,225)	$ (87,649)
Count
Less than 12 months | security	12	12
12 months or longer | security	35	35
Total | security	47	47
Commercial mortgage-backed securities - agency
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	64,074	64,788
Total	64,074	64,788
Unrealized Losses
Less than 12 months	0	0
12 months or longer	(11,708)	(11,288)
Total	$ (11,708)	$ (11,288)
Count
Less than 12 months | security	0	0
12 months or longer | security	17	17
Total | security	17	17
Commercial mortgage-backed securities - non-agency
Fair Value
Less than 12 months	$ 7,735	$ 0
12 months or longer	418,359	507,044
Total	426,094	507,044
Unrealized Losses
Less than 12 months	(78)	0
12 months or longer	(10,102)	(12,116)
Total	$ (10,180)	$ (12,116)
Count
Less than 12 months | security	1	0
12 months or longer | security	16	16
Total | security	17	16
Asset-backed securities
Fair Value
Less than 12 months	$ 132,551	$ 148,063
12 months or longer	64,557	69,307
Total	197,108	217,370
Unrealized Losses
Less than 12 months	(12,303)	(9,723)
12 months or longer	(5,265)	(5,047)
Total	$ (17,568)	$ (14,770)
Count
Less than 12 months | security	4	4
12 months or longer | security	7	7
Total | security	11	11
Corporate bonds
Fair Value
Less than 12 months	$ 61,403	$ 61,031
12 months or longer	57,298	57,138
Total	118,701	118,169
Unrealized Losses
Less than 12 months	(510)	(111)
12 months or longer	(1,897)	(2,058)
Total	$ (2,407)	$ (2,169)
Count
Less than 12 months | security	1	1
12 months or longer | security	8	8
Total | security	9	9