SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	$ 3,302,775	$ 3,448,784
Gross Unrealized Gains	1,406	65,198
Gross Unrealized (Losses)	(352,760)	(32,332)
Total AFS securities, Estimated Fair Value	2,951,421	3,481,650
U.S. government and agency securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	71,665	73,830
Gross Unrealized Gains	0	179
Gross Unrealized (Losses)	(5,925)	(160)
Total AFS securities, Estimated Fair Value	65,740	73,849
Obligations of states and political subdivisions
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	964,651	971,126
Gross Unrealized Gains	578	39,343
Gross Unrealized (Losses)	(142,802)	(2,073)
Total AFS securities, Estimated Fair Value	822,427	1,008,396
Corporate and other bonds
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	184,304	150,201
Gross Unrealized Gains	72	3,353
Gross Unrealized (Losses)	(6,484)	(178)
Total AFS securities, Estimated Fair Value	177,892	153,376
Commercial
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	430,582	468,893
Gross Unrealized Gains	90	6,900
Gross Unrealized (Losses)	(30,837)	(4,636)
Total AFS securities, Estimated Fair Value	399,835	471,157
Commercial | Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	326,117	361,806
Gross Unrealized Gains	90	6,761
Gross Unrealized (Losses)	(27,246)	(4,215)
Total AFS securities, Estimated Fair Value	298,961	364,352
Commercial | Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	104,465	107,087
Gross Unrealized Gains	0	139
Gross Unrealized (Losses)	(3,591)	(421)
Total AFS securities, Estimated Fair Value	100,874	106,805
Residential
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,649,924	1,783,094
Gross Unrealized Gains	666	15,423
Gross Unrealized (Losses)	(166,712)	(25,285)
Total AFS securities, Estimated Fair Value	1,483,878	1,773,232
Residential | Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,571,036	1,691,651
Gross Unrealized Gains	665	15,180
Gross Unrealized (Losses)	(161,629)	(24,337)
Total AFS securities, Estimated Fair Value	1,410,072	1,682,494
Residential | Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	78,888	91,443
Gross Unrealized Gains	1	243
Gross Unrealized (Losses)	(5,083)	(948)
Total AFS securities, Estimated Fair Value	73,806	90,738
Other securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,649	1,640
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Total AFS securities, Estimated Fair Value	$ 1,649	$ 1,640