INVESTMENT SECURITIES - Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Available-for-Sale Portfolio
Amortized Cost	$ 3,500,726	$ 4,675,474
Gross Unrealized Gains	606	565
Gross Unrealized Losses	436,462	524,188
Fair Value	3,064,870	4,151,851
Held-to-Maturity Portfolio
Amortized Cost	1,104,020	1,079,695
Gross Unrealized Gains	0	0
Gross Unrealized Losses	40,576	44,900
Fair Value	1,063,444	1,034,795
Equity Securities, at Fair Value
Amortized Cost	251	251
Gross Unrealized Gains	118	168
Gross Unrealized Losses	0	0
Fair Value	369	419
U.S. Treasury and agency securities
Available-for-Sale Portfolio
Amortized Cost	2,529,014	3,660,546
Gross Unrealized Gains	0	0
Gross Unrealized Losses	339,169	417,009
Fair Value	2,189,845	3,243,537
Held-to-Maturity Portfolio
Amortized Cost	1,094,267	1,079,695
Gross Unrealized Gains	0	0
Gross Unrealized Losses	40,454	44,900
Fair Value	1,053,813	1,034,795
Obligations of state and political subdivisions
Available-for-Sale Portfolio
Amortized Cost	529,922	549,118
Gross Unrealized Gains	577	506
Gross Unrealized Losses	38,536	45,327
Fair Value	491,963	504,297
Government agency mortgage-backed securities
Available-for-Sale Portfolio
Amortized Cost	422,521	444,689
Gross Unrealized Gains	29	58
Gross Unrealized Losses	57,044	60,114
Fair Value	365,506	384,633
Held-to-Maturity Portfolio
Amortized Cost	9,753	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	122	0
Fair Value	9,631	0
Corporate debt securities
Available-for-Sale Portfolio
Amortized Cost	8,000	8,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	903	886
Fair Value	7,097	7,114
Government agency collateralized mortgage obligations
Available-for-Sale Portfolio
Amortized Cost	11,269	13,121
Gross Unrealized Gains	0	1
Gross Unrealized Losses	810	852
Fair Value	10,459	$ 12,270
Held-to-Maturity Portfolio
Fair Value	$ 0