Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings per share [Abstract]
Net income	$ 680	$ 943
Shares [Abstract]
Basic: Weighted average common shares outstanding (in shares)	7,533	7,396
Add: Dilutive effect of outstanding options as determined by the treasury stock method (in shares)	368	49
Diluted: Weighted average common and common equivalent shares outstanding (in shares)	7,901	7,445
Net income per common share [Abstract]
Basic (in dollars per share)	$ 0.09	$ 0.13
Diluted (in dollars per share)	$ 0.09	$ 0.13
Stock Awards [Member]
Earnings per share [Abstract]
Anti-dilutive securities excluded from computation of earnings per dilutive share (in shares)	147	846