Investment securities - Summary of Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost of Held-to-maturity Securities
Amortized Cost, After five but within ten years, Held to maturity	$ 5,940
Amortized Cost, After ten years, Held to maturity	4,444
Amortized Cost, Held to maturity	10,384
Amortized Cost, Mortgage-backed securities, Held to maturity	22,464
Held-to-maturity, Amortized Cost	32,848	$ 7,225
Fair Value of Held-to-maturity Securities
Fair Value, After five but within ten years, Held to maturity	5,938
Fair Value, After ten years, Held to maturity	4,533
Fair Value, Held to maturity	10,471
Fair Value, Mortgage-backed securities, Held to maturity	22,085
Held to maturity, Fair Value	$ 32,556	$ 7,513

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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