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Stock-based Compensation - Weighted-average Assumptions (Details) - $ / shares
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Black-Scholes-Merton option valuation model based on weighted-average assumptions [Abstract]    
Expected term 6 years 5 years 9 months 18 days
Risk-free interest rate 1.00% 0.58%
Expected volatility 127.00% 128.60%
Dividends 0.00% 0.00%
Resulting fair value $ 2.23 $ 1.87