SECURITIES (Securities available for sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Total debt securities	$ 2,066,026
Gross Unrealized Gains	5,586	$ 78,269
Gross Unrealized Losses	(652,801)	(84,233)
Estimated Fair Value	1,733,121
Equity securities with a readily determinable fair value	20,437	20,788
Securities carried at fair value, cost	7,753,433	7,536,338
Carried at fair value (cost of $7,753,433 at June 30, 2022, and $7,536,338 at December 31, 2021)	7,106,218	7,530,374
Total debt securities
Debt Securities, Available-for-sale [Line Items]
Total debt securities	7,732,996	7,515,550
Gross Unrealized Gains	5,586	78,269
Gross Unrealized Losses	(652,801)	(84,233)
Estimated Fair Value	7,085,781	7,509,586
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Total debt securities	13,867	997
Gross Unrealized Gains	24	11
Gross Unrealized Losses	(1)	0
Estimated Fair Value	13,890	1,008
U.S. agencies
Debt Securities, Available-for-sale [Line Items]
Total debt securities	49,837	193,932
Gross Unrealized Gains	0	264
Gross Unrealized Losses	(4,621)	(812)
Estimated Fair Value	45,216	193,384
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total debt securities	1,993,108	2,045,386
Gross Unrealized Gains	49	56,263
Gross Unrealized Losses	(327,814)	(16,616)
Estimated Fair Value	1,665,343	2,085,033
Mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Total debt securities	2,152,926	2,388,601
Gross Unrealized Gains	217	11,870
Gross Unrealized Losses	(187,834)	(51,182)
Estimated Fair Value	1,965,309	2,349,289
Mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Total debt securities	2,285,862	1,749,838
Gross Unrealized Gains	5,290	4,570
Gross Unrealized Losses	(98,715)	(11,029)
Estimated Fair Value	2,192,437	1,743,379
Commercial mortgage-backed securities - agency
Debt Securities, Available-for-sale [Line Items]
Total debt securities	108,950	125,397
Gross Unrealized Gains	0	1,429
Gross Unrealized Losses	(11,099)	(2,914)
Estimated Fair Value	97,851	123,912
Commercial mortgage-backed securities - non-agency
Debt Securities, Available-for-sale [Line Items]
Total debt securities	728,743	600,253
Gross Unrealized Gains	0	998
Gross Unrealized Losses	(14,502)	(363)
Estimated Fair Value	714,241	600,888
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Total debt securities	390,489	408,167
Gross Unrealized Gains	0	2,803
Gross Unrealized Losses	(7,667)	(1,317)
Estimated Fair Value	382,822	409,653
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Total debt securities	9,214	2,979
Gross Unrealized Gains	6	61
Gross Unrealized Losses	(548)	0
Estimated Fair Value	$ 8,672	$ 3,040

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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