Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017
Income taxes [Abstract]
Income tax provision (benefit)	$ (515)	$ (143)	$ (1,901)	$ (54)
Effective tax rate	37.30%	(59.30%)	33.90%	(4.30%)
U.S. corporate income tax rate			21.00%		34.00%
Unrecognized tax benefits that would favorably affect effective income tax rate if recognized	$ 80		$ 80
Unrecognized tax benefits that will lapse upon expiration of statute of limitations	27
Accrued interest and penalties related to uncertain tax positions	$ 15		$ 15