Stockholders' equity (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 shares
Stockholders' equity
Common stock authorized (in shares)		100,000,000	100,000,000
Shares of Common Stock reserved
Total (in shares)		2,442,000	3,346,000
Convertible Notes
Shares of Common Stock reserved
Conversion ratio	0.0236323	0.0236323
Debt conversion converted amount | $		$ 1
Convertible Notes | If Convertible Notes were converted
Shares of Common Stock reserved
Shares issued upon conversion of convertible shares		4,756,000
Stock options
Shares of Common Stock reserved
Outstanding stock options (in shares)		109,000	235,000
RSUs
Shares of Common Stock reserved
Outstanding RSUs (in shares)		951,000	633,000
2001 Plan
Shares of Common Stock reserved
Outstanding stock options (in shares)		0
2001 Plan | Stock options
Shares of Common Stock reserved
Outstanding stock options (in shares)			7,000
2011 Plan
Shares of Common Stock reserved
Number of shares available for grant (in shares)		1,382,000	2,478,000
2011 Plan | Stock options
Shares of Common Stock reserved
Outstanding stock options (in shares)		109,000	228,000
2011 Plan | RSUs
Shares of Common Stock reserved
Outstanding RSUs (in shares)		951,000	633,000