INVESTMENT SECURITIES - Summary of Investments in Debt and Equity Securities Reported in the Financial Statements at an Amount Less Than Their Historical Cost (Details) - Investments reported at less than historical cost - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Schedule of Investments [Line Items]
Historical cost	$ 1,463,842	$ 1,436,638
Fair value	1,272,014	1,267,891
Gross unrealized losses	$ (191,828)	$ (168,747)
Percentage of the Corporation's investment securities available for sale in an unrealized loss position	88.10%	90.10%