Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share, Basic and Diluted [Abstract]
Weighted average common shares outstanding during the period - shares used for basic earnings per common share	9,965	9,864	9,948	9,858
Common shares issuable under share based payment plans which are potentially dilutive	73	43	71	42
Common shares used for diluted earnings per common share	10,038	9,907	10,019	9,900
Net income	$ 1,713	$ 774	$ 3,156	$ 2,594
Earnings per common share:
Basic	$ 0.17	$ 0.08	$ 0.32	$ 0.26
Diluted	$ 0.17	$ 0.08	$ 0.32	$ 0.26