Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings per share [Abstract]
Net income	$ 1,813	$ 883			$ 3,623	$ 2,261
Shares [Abstract]
Basic: Weighted average common shares outstanding (in shares)	7,408	7,498			7,404	7,673
Add: Dilutive effect of outstanding options as determined by the treasury stock method (in shares)	178	51			100	51
Diluted: Weighted average common and common equivalent shares outstanding (in shares)	7,586	7,549			7,504	7,724
Net income per common share [Abstract]
Basic (in dollars per share)	$ 0.24	$ 0.12			$ 0.49	$ 0.29
Diluted (in dollars per share)	$ 0.24	$ 0.12			$ 0.48	$ 0.29
Stock Awards [Member]
Earnings per share [Abstract]
Anti-dilutive securities excluded from computation of earnings per dilutive share (in shares)	382	833	404	833