SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	$ 2,608,028	$ 3,204,361
Gross Unrealized Gains	308	293
Gross Unrealized (Losses)	(523,408)	(462,838)
Total AFS securities, Estimated Fair Value	2,084,928	2,741,816
U.S. government and agency securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	62,221	70,196
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(383)	(8,253)
Total AFS securities, Estimated Fair Value	61,838	61,943
Obligations of states and political subdivisions
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	587,340	959,999
Gross Unrealized Gains	0	137
Gross Unrealized (Losses)	(169,880)	(152,701)
Total AFS securities, Estimated Fair Value	417,460	807,435
Corporate and other bonds
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	267,816	243,979
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(24,998)	(17,599)
Total AFS securities, Estimated Fair Value	242,818	226,380
Commercial
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	287,260	349,598
Gross Unrealized Gains	307	75
Gross Unrealized (Losses)	(52,864)	(43,512)
Total AFS securities, Estimated Fair Value	234,703	306,161
Commercial | Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	215,203	250,186
Gross Unrealized Gains	307	75
Gross Unrealized (Losses)	(50,289)	(39,268)
Total AFS securities, Estimated Fair Value	165,221	210,993
Commercial | Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	72,057	99,412
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(2,575)	(4,244)
Total AFS securities, Estimated Fair Value	69,482	95,168
Residential
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,401,664	1,578,925
Gross Unrealized Gains	1	81
Gross Unrealized (Losses)	(275,283)	(240,773)
Total AFS securities, Estimated Fair Value	1,126,382	1,338,233
Residential | Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,319,987	1,510,110
Gross Unrealized Gains	1	81
Gross Unrealized (Losses)	(268,152)	(233,961)
Total AFS securities, Estimated Fair Value	1,051,836	1,276,230
Residential | Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	81,677	68,815
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(7,131)	(6,812)
Total AFS securities, Estimated Fair Value	74,546	62,003
Other securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,727	1,664
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Total AFS securities, Estimated Fair Value	$ 1,727	$ 1,664