Annual report pursuant to Section 13 and 15(d)

Stock Compensation Plans (Additional Information) (Details)

v3.20.1
Stock Compensation Plans (Additional Information) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Issuance of common stock $ 2,778 $ 4,266 $ 9,066  
Exercise limitation period 10 years      
Total compensation cost not yet recognized, stock options $ 10,793      
Unrecognized compensation cost for stock based compensation, period of recognition 2 years 5 months 30 days      
Options, exercises in period, total intrinsic value $ 7,871 6,171 3,992  
Fair value of stock vested 4,928 3,256 1,944  
Non-cash compensation $ 6,106 $ 5,882 $ 5,539  
Qualified Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) 10,000,000      
Offering date (percent) 5.00%      
Stock issued during period, gross (in shares) 159,212 161,968 167,016  
Shares authorized under stock option plans, exercise price range, lower range limit (in USD per share) $ 2.25 $ 2.21 $ 2.32  
Shares authorized under stock option plans, exercise price range, upper range limit (in USD per share) $ 3.31 $ 3.23 $ 3.00  
Issuance of common stock $ 447 $ 453 $ 420  
Plan 1999        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) 8,728,282      
Granted (in shares) 25,000,000      
Exercise limitation period based on voting power 5 years      
Plan 1999 | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards with annual limit (in shares) 1,500,000     1,500,000
Plan 2009        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) 14,625,416      
Granted (in shares) 0      
Combined voting power (percent) 10.00%      
Fair market value (percent) 100.00%      
Fair market value for ten percent shareholder (percent) 110.00%      
Plan 2009 | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted (in shares)       45,000,000
Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period 4 years