Shareholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends [Abstract]
Dividends declared and paid per common share (in dollars per share)	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.18	$ 0.18
Payment of dividend on common stock	$ 671		$ 663		$ 1,339	$ 1,336
Dividends, date paid	Jun. 14, 2019
Dividends, date of record	May 20, 2019
Stock repurchase program [Abstract]
Common stock repurchased (in shares)	0		33,630		0	156,410

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Aggregate dividends paid during the period for each share of common stock outstanding.

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Date the declared dividend will be paid, in CCYY-MM-DD format.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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No definition available.

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Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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