Stockholders' Equity (Deficit) - Summary of our Outstanding and Exercisable Warrants and Related Transactions (Details) - Warrant [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Class Of Warrant Or Right [Line Items]
Beginning balance, Warrants	6,535
Exercised, Warrants	(1,163)
Expired, Warrants	(245)
Ending balance, Warrants	5,127	6,535
Beginning balance, Weighted Average Exercise Price	$ 1.55
Exercised, Weighted Average Exercise Price	0.31
Expired, Weighted Average Exercise Price	4.80
Ending balance, Weighted Average Exercise Price	$ 1.52	$ 1.55
Warrants, Aggregate Intrinsic Value		$ 1,041
Warrants, Weighted Average Remaining Contractual Life (in Years)	8 years 7 months 6 days	7 years 3 months 18 days