Net Loss Attributable to Common Stockholders Per Share (Schedule of Antidilutive Securities) (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	7,600,514	9,826,045	7,600,514	9,826,045
Convertible preferred stock (on an if-converted basis)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	0	0	0	0
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	7,080,020	9,818,701	7,080,020	9,818,701
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	0	0	0	0
Restricted shares of common stock related to early exercise of options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	520,494	7,344	520,494	7,344
Warrants to purchase Series C convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the calculation of net loss per share (in shares)	0	0	0	0