Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2017
Income taxes [Abstract]
Income tax provision (benefit)	$ (439)	$ (515)	$ (1,682)	$ (1,901)
Effective tax rate	(93.20%)	37.30%	33.00%	33.90%
U.S. corporate income tax rate			21.00%		34.00%
Unrecognized tax benefits that would favorably affect effective income tax rate if recognized	$ 97		$ 97
Unrecognized tax benefits that will lapse upon expiration of statute of limitations		$ 24
Accrued interest and penalties related to uncertain tax positions	$ 17		$ 17