Shareholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 26,014
Net income	$ 2,574	$ 1,813	4,464	$ 3,623
Share-based compensation expense			524
Issuance of shares from exercise of stock options			229
Relinquishment of stock awards upon exercise and fully vested deferred stock units			(265)
Foreign currency translation adjustment	11	$ 3	0	$ 10
Purchase of common stock for treasury			(2,000)
Dividends declared and paid on common stock			(2,001)
Ending balance	$ 26,965		$ 26,965
Dividends [Abstract]
Dividends declared and paid per common share (in dollars per share)	$ 0.09	$ 0.09	$ 0.27	$ 0.26
Dividends paid date	Sep. 14, 2018
Dividends record date	Aug. 20, 2018
Payment of dividend on common stock	$ 665	$ 661	$ 2,001	$ 1,911

Amount of increase to additional paid-in capital (APIC) from recognition of equity-based compensation.

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