Investment securities - Summary of Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment securities
Amortized Cost, After ten years, Held to maturity	$ 6,861
Amortized Cost, Held to maturity	6,861
Amortized Cost, Mortgage-backed securities, Held to maturity	3,319
Held-to-maturity, Amortized Cost	10,180	$ 10,517
Fair Value, After ten years, Held to maturity	6,864
Fair Value, Held to maturity	6,864
Fair Value, Mortgage-backed securities, Held to maturity	3,495
Held to maturity, Fair Value	$ 10,359	$ 10,714

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of held-to-maturity debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing after the tenth fiscal year following the latest fiscal year.

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Amount of investment in held-to-maturity debt securities with a single maturity date, after other than temporary impairment (OTTI) accretion.

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Fair value of investment in held-to-maturity debt securities with a single maturity date.

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Amount of held-to-maturity debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.

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Fair value of investments in debt securities classified as held-to-maturity.

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