Debt and lease liabilities (Finance Lease Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt And Leases [Abstract]
Interest rate	9.64%		9.64%
Weighted average interest rate	2.75%	0.47%	2.75%	0.47%
Weighted average lease term	10 months 24 days	9 months 3 days	10 months 24 days	9 months 3 days
Interest expense	$ 42	$ 20	$ 94	$ 46