Derivatives and hedging activities - Offsetting, Derivative assets and derivative liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Offsetting Derivative Assets [Abstract]
Gross amounts presented in the consolidated balance sheet	$ 3,258	$ 1,365
Gross amounts not offset in the consolidated balance sheet subject to netting agreements	(618)	(232)
Net amounts	2,640	1,133
Offsetting Derivative Liabilities [Abstract]
Gross amounts presented in the consolidated balance sheet	(1,514)	(423)
Gross amounts not offset in the consolidated balance sheet subject to netting agreements	618	232
Net amounts	$ (896)	$ (191)

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement, deducted from derivative assets.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement, deducted from derivative liabilities.

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