Other accrued expenses and other non-current liabilities - Other accrued expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Other accrued expenses and other non-current liabilities
Accrued inventory	$ 999	$ 459
Accrued royalties	535	476
Accrued professional services	692	655
Accrued development costs	121	151
Accrued other	721	757
Total accrued expenses	$ 3,068	$ 2,498