Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Stock-Based Compensation - Summary of Non-Employee RSU Activity (Details)

v3.20.4
Stock-Based Compensation Stock-Based Compensation - Summary of Non-Employee RSU Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted Average Remaining Contractual Term (years), Outstanding 1 year 8 months 12 days 2 years 8 months 12 days  
Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested as of December 31 (in shares) 131,600    
Outstanding as of December 31 (in shares) 638,300 670,800  
Restricted Stock Units that may be settled in cash      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding as of December 31 (in shares) 8,334 14,118  
2016 Directors' Plan | Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested as of December 31 (in shares) 260,300    
Granted (in shares) 171,200 57,000.0 67,300
Weighted-average grant date fair value of PSUs and RSUs (in dollars per share) $ 3.83 $ 11.05 $ 13.30
Exercised (in dollars per share) $ 11.05    
Number of Shares, Exercised (in shares) (19,000.0)    
Outstanding as of December 31 (in shares) 412,500    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price $ 9.32 $ 13.07  
Award vesting period 1 year