Net Loss Attributable to Common Stockholders Per Share (Schedule of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator
Net loss attributable to common stockholders	$ (20,403)	$ (8,601)	$ (53,992)	$ (29,456)
Cumulative undeclared dividends on Series D convertible preferred stock	0	(140)	0	(1,735)
Net loss attributable to common stockholders, basic	(20,403)	(8,741)	(53,992)	(31,191)
Net loss attributable to common stockholders, diluted	$ (20,403)	$ (8,741)	$ (53,992)	$ (31,191)
Denominator
Weighted-average shares used to compute net income per share, basic (in shares)	67,213,282	53,596,982	66,428,303	20,041,080
Weighted-average shares used to compute net income per share, diluted (in shares)	67,213,282	53,596,982	66,428,303	20,041,080
Net loss per share
Net loss attributable to common stockholders per share, basic (in dollars per share)	$ (0.30)	$ (0.16)	$ (0.81)	$ (1.56)
Net loss attributable to common stockholders per share, diluted (in dollars per share)	$ (0.30)	$ (0.16)	$ (0.81)	$ (1.56)