Other accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other accrued expenses
Accrued inventory	$ 599	$ 835
Accrued royalties	323	221
Accrued professional services	723	346
Accrued development costs	795	1,559
Accrued other	689	599
Total accrued expenses	$ 3,129	$ 3,560