v3.20.4
Stock incentive plans - Restricted stock unit awards (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Dec. 31, 2020
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Stock incentive plans        
Shares of common stock issued resulting from vesting     302,000  
RSUs        
Stock incentive plans        
Total unrecognized stock-based compensation expense $ 9,907   $ 9,907  
Weighted average period over which unrecognized compensation expense is expected to be recognized 1 year 8 months 12 days      
Number of Shares        
Non-vested at beginning of period (in shares)     633,000  
Granted (in shares)     898,000  
Vested (in shares)     (453,000)  
Canceled/forfeited (in shares)     (127,000)  
Non-vested at end of period (in shares) 951,000   951,000 633,000
Weighted Average Grant Date Fair Value        
Non-vested at beginning of period (in dollars per share)     $ 22.04  
Granted (in dollars per share)     11.06  
Vested (in dollars per share)     18.28  
Canceled/forfeited (in dollars per share)     15.75  
Non-vested at end of period (in dollars per share) $ 14.30   $ 14.30 $ 22.04
Service based-restricted stock unit awards | Executive And Non Executive Member | Maximum        
Stock incentive plans        
Vesting period     3 years  
Service based-restricted stock unit awards | Non-employee directors and existing members        
Stock incentive plans        
Vesting period     1 year  
Service based-restricted stock unit awards | Non-employee directors and new members        
Stock incentive plans        
Vesting percentage when the individual completes 12 months of continuous service 33.30%   33.30%  
Vesting period     3 years  
Performance-based restricted stock unit awards        
Stock incentive plans        
Vesting period     3 years 3 years
Number of Shares        
Granted (in shares)     36,000  
Weighted Average Grant Date Fair Value        
Granted (in dollars per share)     $ 12.41  
Performance-based restricted stock unit awards | Minimum        
Stock incentive plans        
Performance objective threshold (as a percent) 50.00%   50.00%  
Performance-based restricted stock unit awards | Maximum        
Stock incentive plans        
Performance objective threshold (as a percent) 150.00%   150.00%  
2018 performance-based RSUs        
Stock incentive plans        
Performance objective achieved (as a percent)   100.50%    
2019 performance-based RSUs        
Stock incentive plans        
Performance objective achieved (as a percent)   95.00%    
Number of awards excluded from granted and non-vested as the performance targets have not yet been defined 32,000   32,000  
2020 performance-based RSUs        
Stock incentive plans        
Performance objective achieved (as a percent)   97.00%    
Number of awards excluded from granted and non-vested as the performance targets have not yet been defined 151,000   151,000