INVESTMENT SECURITIES - Investment Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	1,242	240
12 months or longer	109	66
Total	1,351	306
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 4,367,516	$ 1,395,578
12 months or longer	902,376	967,788
Total	5,269,892	2,363,366
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	356,573	17,505
12 months or longer	311,052	93,774
Total	667,625	$ 111,279
Available-for-sale, allowance for credit losses	0
Available-for-sale Securities [Member]
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Accrued interest receivable	$ 20,200
U.S. Treasury and Agency Securities
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	109	47
12 months or longer	18	13
Total	127	60
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 3,693,538	$ 1,224,101
12 months or longer	797,349	900,462
Total	4,490,887	2,124,563
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	291,840	14,873
12 months or longer	292,524	91,184
Total	$ 584,364	$ 106,057
Obligations of State and Political Subdivisions
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	514	27
12 months or longer	0	0
Total	514	27
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 348,257	$ 23,966
12 months or longer	0	0
Total	348,257	23,966
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	40,770	56
12 months or longer	0	0
Total	$ 40,770	$ 56
Government Agency Mortgage-Backed Securities
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	578	147
12 months or longer	90	52
Total	668	199
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 304,192	$ 139,442
12 months or longer	105,017	67,273
Total	409,209	206,715
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	22,788	2,475
12 months or longer	18,528	2,590
Total	$ 41,316	$ 5,065
Corporate debt securities
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	2	1
12 months or longer	0	0
Total	2	1
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 7,231	$ 4,923
12 months or longer	0	0
Total	7,231	4,923
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	769	77
12 months or longer	0	0
Total	$ 769	$ 77
Government Agency Collateralized Mortgage Obligations
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 months	39	18
12 months or longer	1	1
Total	40	19
Available-for-Sale Securities, in Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 14,298	$ 3,146
12 months or longer	10	53
Total	14,308	3,199
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 months	406	24
12 months or longer	0	0
Total	$ 406	$ 24