Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income taxes
Income tax expense	$ 109	$ 143	$ 225	$ 254
Effective tax rate (as a percent)	3.70%	357.50%	1.60%	5.20%