Annual report pursuant to Section 13 and 15(d)

Stock Compensation Plans (Additional Information) (Details)

v3.19.1
Stock Compensation Plans (Additional Information) (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Issuance of common stock $ 4,266,000 $ 9,066,000 $ 3,061,000  
Exercise limitation period 10 years      
Total compensation cost not yet recognized, stock options $ 7,931      
Unrecognized compensation cost for stock based compensation, period of recognition 2 years 5 months 15 days      
Options, exercises in period, total intrinsic value $ 6,171,000 3,992,000 6,556,000  
Fair value of stock vested 3,256,000 1,944,000    
Non-cash compensation $ 5,882,000 $ 5,539,000 $ 5,311,000  
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) 161,968 167,016 210,330  
Shares authorized under stock option plans, exercise price range, lower range limit (in USD per share) $ 2.21 $ 2.32 $ 2.19  
Shares authorized under stock option plans, exercise price range, upper range limit (in USD per share) $ 3.23 $ 3.00 $ 2.38  
Issuance of common stock $ 453,000 $ 420,000 $ 481,000  
Plan 1999        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) 7,412,868      
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) 16,721,103      
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