Debt Securities Held-to-maturity - Credit quality indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	$ 8,390,024	$ 8,852,825
Obligations of Puerto Rico, States and political subdivisions
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	57,845	65,408
Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	12,615	18,820
Watch | Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	1,555	2,255
Pass | Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	$ 11,060	$ 16,565