Debt Securities Held-to-maturity - Credit quality indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt securities held to maturity credit quality indicator
Held to maturity securities	$ 89,725	$ 92,621
Obligations of Puerto Rico, States and political subdivisions
Debt securities held to maturity credit quality indicator
Held to maturity securities	78,133	81,029
Obligations of Puerto Rico, States and political subdivisions | Munis Payable From Real and Personal Property Taxes
Debt securities held to maturity credit quality indicator
Held to maturity securities	32,590	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
Held to maturity securities	$ 32,590	$ 35,315