INVESTMENT SECURITIES - Amortized Cost of Investment Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Total	$ 2,213,833	$ 2,287,372
Aaa
Schedule of Held-to-maturity Securities [Line Items]
Total	185,294
Aa1
Schedule of Held-to-maturity Securities [Line Items]
Total	153,408
Aa2
Schedule of Held-to-maturity Securities [Line Items]
Total	181,369
Aa3
Schedule of Held-to-maturity Securities [Line Items]
Total	133,499
A1
Schedule of Held-to-maturity Securities [Line Items]
Total	131,310
A2
Schedule of Held-to-maturity Securities [Line Items]
Total	10,172
A3
Schedule of Held-to-maturity Securities [Line Items]
Total	10,125
Non-rated
Schedule of Held-to-maturity Securities [Line Items]
Total	1,408,656
State and municipal
Schedule of Held-to-maturity Securities [Line Items]
Total	1,107,325	$ 1,117,552
State and municipal | Aaa
Schedule of Held-to-maturity Securities [Line Items]
Total	114,709
State and municipal | Aa1
Schedule of Held-to-maturity Securities [Line Items]
Total	153,408
State and municipal | Aa2
Schedule of Held-to-maturity Securities [Line Items]
Total	181,369
State and municipal | Aa3
Schedule of Held-to-maturity Securities [Line Items]
Total	133,499
State and municipal | A1
Schedule of Held-to-maturity Securities [Line Items]
Total	131,310
State and municipal | A2
Schedule of Held-to-maturity Securities [Line Items]
Total	10,172
State and municipal | A3
Schedule of Held-to-maturity Securities [Line Items]
Total	10,125
State and municipal | Non-rated
Schedule of Held-to-maturity Securities [Line Items]
Total	372,733
Other
Schedule of Held-to-maturity Securities [Line Items]
Total	1,106,508
Other | Aaa
Schedule of Held-to-maturity Securities [Line Items]
Total	70,585
Other | Aa1
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | Aa2
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | Aa3
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | A1
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | A2
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | A3
Schedule of Held-to-maturity Securities [Line Items]
Total	0
Other | Non-rated
Schedule of Held-to-maturity Securities [Line Items]
Total	$ 1,035,923