SECURITIES (Debt securities available for sale) (Details) $ in Thousands	Jun. 30, 2021 USD ($) bankLocation	Dec. 31, 2020 USD ($) bankLocation
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 2,324,495	$ 1,672,530
Unrealized Losses, Less than 12 months	$ (35,342)	$ (18,373)
Count, Less than 12 months \| bankLocation	196	127
Fair Value, 12 months or longer	$ 129,627	$ 508,436
Unrealized Losses, 12 months or longer	$ (2,617)	$ (5,743)
Count, 12 months or longer \| bankLocation	24	103
Fair Value, Total	$ 2,454,122	$ 2,180,966
Unrealized Losses, Total	$ (37,959)	$ (24,116)
Count, Total \| bankLocation	220	230
U.S. agencies
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 18,983	$ 2,981
Unrealized Losses, Less than 12 months	$ (492)	$ (8)
Count, Less than 12 months \| bankLocation	1	5
Fair Value, 12 months or longer	$ 0	$ 99,922
Unrealized Losses, 12 months or longer	$ 0	$ (918)
Count, 12 months or longer \| bankLocation	0	72
Fair Value, Total	$ 18,983	$ 102,903
Unrealized Losses, Total	$ (492)	$ (926)
Count, Total \| bankLocation	1	77
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 591,597	$ 346,598
Unrealized Losses, Less than 12 months	$ (11,887)	$ (2,959)
Count, Less than 12 months \| bankLocation	107	49
Fair Value, 12 months or longer	$ 6,719	$ 0
Unrealized Losses, 12 months or longer	$ (72)	$ 0
Count, 12 months or longer \| bankLocation	2	0
Fair Value, Total	$ 598,316	$ 346,598
Unrealized Losses, Total	$ (11,959)	$ (2,959)
Count, Total \| bankLocation	109	49
Mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 1,025,619	$ 653,793
Unrealized Losses, Less than 12 months	$ (19,499)	$ (12,342)
Count, Less than 12 months \| bankLocation	58	35
Fair Value, 12 months or longer	$ 37,181	$ 31,012
Unrealized Losses, 12 months or longer	$ (1,105)	$ (381)
Count, 12 months or longer \| bankLocation	4	3
Fair Value, Total	$ 1,062,800	$ 684,805
Unrealized Losses, Total	$ (20,604)	$ (12,723)
Count, Total \| bankLocation	62	38
Mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 541,131	$ 378,843
Unrealized Losses, Less than 12 months	$ (1,345)	$ (1,639)
Count, Less than 12 months \| bankLocation	12	17
Fair Value, 12 months or longer	$ 33,988	$ 1,622
Unrealized Losses, 12 months or longer	$ (430)	$ (1)
Count, 12 months or longer \| bankLocation	5	1
Fair Value, Total	$ 575,119	$ 380,465
Unrealized Losses, Total	$ (1,775)	$ (1,640)
Count, Total \| bankLocation	17	18
Commercial mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 69,690	$ 46,541
Unrealized Losses, Less than 12 months	$ (1,800)	$ (738)
Count, Less than 12 months \| bankLocation	11	6
Fair Value, 12 months or longer	$ 0	$ 0
Unrealized Losses, 12 months or longer	$ 0	$ 0
Count, 12 months or longer \| bankLocation	0	0
Fair Value, Total	$ 69,690	$ 46,541
Unrealized Losses, Total	$ (1,800)	$ (738)
Count, Total \| bankLocation	11	6
Commercial mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 0	$ 100,042
Unrealized Losses, Less than 12 months	$ 0	$ (15)
Count, Less than 12 months \| bankLocation	0	2
Fair Value, 12 months or longer	$ 15,960	$ 35,428
Unrealized Losses, 12 months or longer	$ (200)	$ (676)
Count, 12 months or longer \| bankLocation	2	3
Fair Value, Total	$ 15,960	$ 135,470
Unrealized Losses, Total	$ (200)	$ (691)
Count, Total \| bankLocation	2	5
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 77,475	$ 141,824
Unrealized Losses, Less than 12 months	$ (319)	$ (643)
Count, Less than 12 months \| bankLocation	7	9
Fair Value, 12 months or longer	$ 35,779	$ 340,452
Unrealized Losses, 12 months or longer	$ (810)	$ (3,767)
Count, 12 months or longer \| bankLocation	11	24
Fair Value, Total	$ 113,254	$ 482,276
Unrealized Losses, Total	$ (1,129)	$ (4,410)
Count, Total \| bankLocation	18	33
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 0	$ 1,908
Unrealized Losses, Less than 12 months	$ 0	$ (29)
Count, Less than 12 months \| bankLocation	0	4
Fair Value, 12 months or longer	$ 0	$ 0
Unrealized Losses, 12 months or longer	$ 0	$ 0
Count, 12 months or longer \| bankLocation	0	0
Fair Value, Total	$ 0	$ 1,908
Unrealized Losses, Total	$ 0	$ (29)
Count, Total \| bankLocation	0	4

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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