Summary of Significant Accounting Policies - Earning 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
Accounting Policies [Abstract]
Net loss	$ (14,103)	$ (14,580)	$ (12,822)	$ (12,008)	$ (12,606)	$ (13,126)	$ (41,505)	$ (37,741)
Weighted-average common stock outstanding, basic (in shares)	11,580,000			4,329,000			7,361,000	3,327,000
Weighted-average common stock outstanding, diluted (in shares)	11,580,000			4,329,000			7,361,000	3,327,000
Net loss per share, basic (in dollars per share)	$ (1.22)			$ (2.77)			$ (5.64)	$ (11.34)
Net loss per share, diluted (in dollars per share)	$ (1.22)			$ (2.77)			$ (5.64)	$ (11.34)