Debt and lease liabilities (Finance Lease Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt And Leases [Abstract]
Interest rate	9.64%		9.64%
Weighted average interest rate	3.17%	1.83%	3.17%	1.83%
Weighted average lease term	8 months 23 days	1 year 3 days	8 months 23 days	1 year 3 days
Interest expense	$ 34	$ 56	$ 128	$ 102