Debt Securities Held-to-maturity - Credit quality indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt securities held to maturity credit quality indicator
Debt securities held-to-maturity	$ 93,163	$ 97,662
Obligations of Puerto Rico, States and political subdivisions
Debt securities held to maturity credit quality indicator
Debt securities held-to-maturity	81,067	$ 85,556
Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator
Debt securities held-to-maturity	35,315
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
Debt securities held-to-maturity	20,585
Special Mention | Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator
Debt securities held-to-maturity	$ 14,730