Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Income taxes [Abstract]
Income tax provision	$ (143)	$ 581	$ (54)	$ 1,064
Effective tax rate	(59.30%)	18.40%	(4.30%)	19.20%
Unrecognized tax benefits that would favorably affect effective income tax rate if recognized	$ 79		$ 79
Unrecognized tax benefits that will lapse upon expiration of statute of limitations	25
Accrued interest and penalties related to uncertain tax positions	$ 15		$ 15
U.S. corporate income tax rate					34.00%
Maximum [Member]
Income taxes [Abstract]
U.S. corporate income tax rate					35.00%