Net Loss per share (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net loss per share
Change in fair value of the bifurcated derivative			$ (25,556)
Interest expense			$ 3,071
Number of shares at issue			20,936,548
Number of shares at issuance			20,936,548
Number of days outstanding to calculate weighted average shares			76 days
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	24,050,691	56,910,149	12,829,617
Weighted-average number of shares of adjustments			4,359,391
Stock options
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	12,690,745	17,258,524	12,522,867
Restricted stock units
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,649,317	678,089	306,750
Employee Stock purchase plan
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	53,372	227,141
5.00% Convertible Senior Notes due 2048 | Convertible Common Stock [Member]
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	41,873	3,950,032
5.00% Convertible Senior Second Lien Notes due 2048 | Convertible Common Stock [Member]
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)		34,796,363
5.00% Convertible Senior Third Lien Notes due 2048 | Convertible Common Stock [Member]
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	8,615,384