Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings per share [Abstract]
Net income	$ 2,574	$ 1,813	$ 4,464	$ 3,623
Shares [Abstract]
Basic: Weighted average common shares outstanding (in shares)	7,413	7,408	7,449	7,404
Add: Dilutive effect of outstanding options and restricted stock units as determined by the treasury stock method (in shares)	345	178	325	100
Diluted: Weighted average common and common equivalent shares outstanding (in shares)	7,758	7,586	7,774	7,504
Net income per common share [Abstract]
Basic (in dollars per share)	$ 0.35	$ 0.24	$ 0.60	$ 0.49
Diluted (in dollars per share)	$ 0.33	$ 0.24	$ 0.57	$ 0.48
Stock Awards [Member]
Earnings per share [Abstract]
Anti-dilutive securities excluded from computation of earnings per dilutive share (in shares)	147	382	149	404