Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings per share [Abstract]
Net income	$ 867	$ 753	$ 1,810	$ 1,378
Shares [Abstract]
Basic: Weighted average common shares outstanding (in shares)	7,408	7,689	7,402	7,761
Add: Dilutive effect of outstanding options as determined by the treasury stock method (in shares)	106	54	67	52
Diluted: Weighted average common and common equivalent shares outstanding (in shares)	7,514	7,743	7,469	7,813
Net income per common share [Abstract]
Basic (in dollars per share)	$ 0.12	$ 0.10	$ 0.24	$ 0.18
Diluted (in dollars per share)	$ 0.12	$ 0.10	$ 0.24	$ 0.18
Stock Awards [Member]
Earnings per share [Abstract]
Anti-dilutive securities excluded from computation of earnings per dilutive share (in shares)	407	827	732	827