Other accrued expenses - Other accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other accrued expenses
Accrued inventory	$ 459	$ 599
Accrued royalties	476	323
Accrued professional services	655	723
Accrued development costs	151	795
Accrued other	757	689
Total accrued expenses	$ 2,498	$ 3,129