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Fair Value Measurements - Financial Instruments Measured on a Recurring Basis (Details) - USD ($)
9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Phantom Stock Units    
Financial instruments measured at fair value on a recurring basis    
Expected dividends $ 0  
Minimum | Phantom Stock Units    
Financial instruments measured at fair value on a recurring basis    
Grant date fair value (in dollars per share) $ 1.70  
Risk free interest rate (as a percent) 0.27%  
Expected life (years) 2 years 8 months 15 days  
Estimated volatility factor (as a percent) 65.10%  
Maximum | Phantom Stock Units    
Financial instruments measured at fair value on a recurring basis    
Grant date fair value (in dollars per share) $ 7.28  
Risk free interest rate (as a percent) 2.39%  
Expected life (years) 2 years 9 months  
Estimated volatility factor (as a percent) 69.90%  
Liability-classified stock compensation | Level 3    
Financial instruments measured at fair value on a recurring basis    
Fair value of liability $ 198,000  
Liability-classified stock compensation | Recurring | Level 3    
Financial instruments measured at fair value on a recurring basis    
Fair value of liability $ 198,000 $ 282,000