Other accrued expenses and other non-current liabilities - Other accrued expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Other accrued expenses and other non-current liabilities
Accrued inventory	$ 485	$ 599
Accrued royalties	493	323
Accrued professional services	878	723
Accrued development costs	735	795
Accrued other	948	689
Total accrued expenses	$ 3,539	$ 3,129