SECURITIES (Securities available for sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	$ 6,800	$ 78,269
Gross Unrealized Losses	(393,442)	(84,233)
Equity securities with a readily determinable fair value	20,531	20,788
Amortized Cost, Total	7,411,885	7,536,338
Estimated Fair Value, Total	7,025,243	7,530,374
Total debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,391,354	7,515,550
Gross Unrealized Gains	6,800	78,269
Gross Unrealized Losses	(393,442)	(84,233)
Estimated Fair Value	7,004,712	7,509,586
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	998	997
Gross Unrealized Gains	3	11
Gross Unrealized Losses	0	0
Estimated Fair Value	1,001	1,008
U.S. agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	89,827	193,932
Gross Unrealized Gains	24	264
Gross Unrealized Losses	(3,742)	(812)
Estimated Fair Value	86,109	193,384
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,808,169	2,045,386
Gross Unrealized Gains	274	56,263
Gross Unrealized Losses	(170,526)	(16,616)
Estimated Fair Value	1,637,917	2,085,033
Mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,264,657	2,388,601
Gross Unrealized Gains	1,510	11,870
Gross Unrealized Losses	(138,004)	(51,182)
Estimated Fair Value	2,128,163	2,349,289
Mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,071,559	1,749,838
Gross Unrealized Gains	4,529	4,570
Gross Unrealized Losses	(62,152)	(11,029)
Estimated Fair Value	2,013,936	1,743,379
Commercial mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	127,563	125,397
Gross Unrealized Gains	107	1,429
Gross Unrealized Losses	(9,115)	(2,914)
Estimated Fair Value	118,555	123,912
Commercial mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	699,703	600,253
Gross Unrealized Gains	0	998
Gross Unrealized Losses	(5,740)	(363)
Estimated Fair Value	693,963	600,888
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	321,155	408,167
Gross Unrealized Gains	320	2,803
Gross Unrealized Losses	(4,055)	(1,317)
Estimated Fair Value	317,420	409,653
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,723	2,979
Gross Unrealized Gains	33	61
Gross Unrealized Losses	(108)	0
Estimated Fair Value	$ 7,648	$ 3,040

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