Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Income taxes [Abstract]
Income tax provision	$ 429	$ 355	$ 888	$ 666
Effective tax rate	33.10%	32.00%	32.90%	32.60%
Total gross unrecognized tax benefits that would impact the effective rate	$ 111		$ 111
Previously unrecognized tax benefit recognized	31
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 25		$ 25