Net Loss Per Share of Common Stock - Computation of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss - basic and diluted	$ (10,755)	$ (25,952)	$ (7,077)	$ (10,474)	$ (3,614)	$ (3,944)	$ (43,784)	$ (18,032)
Deemed dividend related to Warrant Exchange	0			0			0	(12,546)
Net loss to common stockholders	(10,755)			(10,474)			(43,784)	(30,578)
Net loss to common stockholders	$ (10,755)			$ (10,474)			$ (43,784)	$ (30,578)
Shares used in calculating net loss per common share - basic (in shares)	198,790,980			141,591,218			193,599,525	92,764,157
Shares used in calculating net loss per common share - diluted (in shares)	198,790,980			141,591,218			193,599,525	92,764,157
Net loss per share of common stock - diluted (in USD per share)	$ (0.05)			$ (0.07)			$ (0.23)	$ (0.33)
Net loss per common share - basic and diluted (in USD per share)	$ (0.05)			$ (0.07)			$ (0.23)	$ (0.33)