Debt and capital lease obligations - Debt components (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total minimum principal payments	$ 34,976	$ 34,976
Unamortized debt discount	(489)	(515)
Accretion of final fee	139	59
Total debt, net	34,626	34,520
Amount included as short-term	(1,238)	(1,032)
Long-term debt, net of current portion and debt discount	33,388	33,488
Midcap Trust Term Loan
Debt Instrument [Line Items]
Total minimum principal payments	32,500	32,500
PPP loan
Debt Instrument [Line Items]
Total minimum principal payments	2,476	$ 2,476
Amount included as short-term	(1,200)
Long-term debt, net of current portion and debt discount	$ 1,300