Debt Securities Held-to-maturity - Credit quality indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	$ 9,004,729	$ 9,356,739
Obligations of Puerto Rico, States and political subdivisions
Debt securities held to maturity credit quality indicator [Line Items]
Held to maturity securities	65,802	65,921
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	18,820	24,660
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	2,255	13,735
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	$ 16,565	$ 10,925