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Basis of Presentation and Significant Accounting Policies - Stock-Based Compensation (Details)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2022
USD ($)
plan
$ / shares
shares
Dec. 31, 2021
USD ($)
$ / shares
shares
Sep. 30, 2021
USD ($)
Jun. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
$ / shares
shares
Dec. 31, 2021
USD ($)
$ / shares
shares
Dec. 31, 2020
shares
Oct. 31, 2021
USD ($)
Jun. 16, 2021
shares
Jun. 30, 2018
shares
Stock-Based Compensation                    
Number of employee share-based compensation plans | plan 3                  
Weighted-average assumptions used to estimate the fair value of each stock option                    
Dividend (as a percent) 0.00%       0.00%          
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]                    
Cash received from the exercise of stock options and ESPP | $ $ 620       $ 1,286          
Directors' deferred share unit compensation | $ $ 211 $ 209 $ 179 $ 144 149          
ESPP                    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]                    
Aggregate number of common shares reserved for future issuance                   2,000,000
Stock options and restricted stock awards                    
Stock-Based Compensation                    
Vesting period 3 years                  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]                    
Stock compensation expense | $ $ 4,200       $ 3,700          
Estimated fair value that could be expensed | $ $ 46,900                  
Stock options                    
Weighted-average assumptions used to estimate the fair value of each stock option                    
Dividend (as a percent) 0.00%       0.00%          
Volatility (as a percent) 83.00%       85.40%          
Risk-free interest rate (as a percent) 1.81%       0.62%          
Expected life 6 years       6 years          
Weighted-average grant date fair value (in dollars per share) | $ / shares $ 3.78       $ 5.47          
Number of Stock Options                    
Outstanding at the beginning of the period (in shares) 21,219,000                  
Granted (in shares) 5,957,000                  
Exercised (in shares) (173,000)                  
Forfeited/Canceled (in shares) (66,000)                  
Outstanding at the end of the period (in shares) 26,937,000 21,219,000       21,219,000        
Weighted-Average Exercise Price                    
Outstanding at the beginning of the period (in dollars per share) | $ / shares $ 6.28                  
Granted (in dollars per share) | $ / shares 5.34                  
Exercised (in dollars per share) | $ / shares 3.59                  
Forfeited/Canceled (in dollars per share) | $ / shares 10.51                  
Outstanding at the end of the period (in dollars per share) | $ / shares $ 6.08 $ 6.28       $ 6.28        
Performance shares                    
Number of Stock Options                    
Granted (in shares)             2,600,000      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]                    
Stock compensation expense | $           $ 2,600        
Estimated fair value that could be expensed | $               $ 7,800    
Restricted stock                    
Number of Restricted Stock Shares                    
Unvested at the beginning of the period (in shares) 77,000                  
Vested (in shares) (2,000)                  
Unvested at the end of the period (in shares) 75,000 77,000       77,000        
Weighted-Average Grant Date Fair Value                    
Unvested at the beginning of the period (in dollars per share) | $ / shares $ 5.59                  
Vested (in dollars per share) | $ / shares 2.53                  
Unvested at the end of the period (in dollars per share) | $ / shares $ 5.68 $ 5.59       $ 5.59        
2018 Plan                    
Stock-Based Compensation                    
Common stock authorized for issuance (in shares)         22,392,986       6,600,000  
Inducement Plan                    
Stock-Based Compensation                    
Number of employee share-based compensation plans | plan 2                  
Common stock authorized for issuance (in shares) 7,000,000                  
2018 Plan and Inducement Plan                    
Stock-Based Compensation                    
Exercise period 10 years                  
2018 Plan and Inducement Plan | Maximum                    
Stock-Based Compensation                    
Vesting period 4 years