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Warrants to Acquire Shares of Common Stock - Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model (Details) - $ / shares
shares in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Class of Warrant or Right [Line Items]    
Warrants outstanding (in shares) 559 1,392
Other warrants (liability-classified)    
Class of Warrant or Right [Line Items]    
Warrants outstanding (in shares) 13 13
Strike price (in dollars per share) $ 7.50 $ 7.50
Expected term (years) 2 years 3 months 3 days 2 years 9 months
Volatility % 151.45% 150.38%
Risk-free rate % 0.30% 0.16%