Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income taxes [Abstract]
Income tax provision	$ 769	$ 344	$ 1,010	$ 1,657	$ 1,010
Effective tax rate	29.80%	28.00%	30.90%	31.40%
Total gross unrecognized tax benefits that would impact the effective rate	$ 80			$ 80
Previously unrecognized tax benefit recognized	31
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 14			$ 14