INVESTMENT SECURITIES - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) - Investments reported at less than historical cost - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Historical cost	$ 1,839,685	$ 1,781,108
Fair value	1,591,663	1,560,554
Gross unrealized losses	$ 248,022	$ 220,554
Percent of the Corporation's investments available for sale	98.20%	95.90%