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Fair Value Measurements - Weighted average (in aggregate) significant unobservable inputs (Details) - Fair Value, Inputs, Level 3 [Member] - $ / shares
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Warrant Liability [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Strike price $ 0.26 $ 0.28
Contractual term (years) 1 year 1 month 6 days 1 year 7 months 6 days
Volatility (annual) 79.00% 116.00%
Risk-free rate 0.10% 0.20%
Dividend yield (per share) 0.00% 0.00%
Contingent Payable Derivative Liability [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Strike price $ 1.47 $ 1.53
Contractual term (years) 1 year 6 months 1 year 4 months 24 days
Volatility (annual) 112.00% 126.00%
Risk-free rate 0.20% 0.10%
Dividend yield (per share) 0.00% 0.00%
Embedded Conversion Option [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Strike price   $ 0.59
Contractual term (years)   10 months 24 days
Volatility (annual)   106.00%
Risk-free rate   0.10%
Dividend yield (per share)   0.00%