INVESTMENT SECURITIES - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) - Investments reported at less than historical cost - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Historical cost	$ 1,882,899	$ 2,207,633
Fair value	1,500,101	1,910,508
Gross unrealized losses	$ 382,798	$ 297,125
Percent of the Corporation's investments available for sale	99.99%	96.65%