Annual report pursuant to Section 13 and 15(d)

Stock Compensation Plans (Additional Information) (Details)

v3.8.0.1
Stock Compensation Plans (Additional Information) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Issuance of common stock $ 9,066 $ 3,061 $ 2,016  
Exercise limitation period 10 years      
Total compensation cost not yet recognized, stock options $ 7,371      
Unrecognized compensation cost for stock based compensation, period of recognition 2 years 1 month 1 day      
Options, exercises in period, total intrinsic value $ 3,992 6,556 2,595  
Fair value of stock vested 1,944 1,197    
Allocated share-based compensation expense $ 5,539 $ 5,311 $ 8,759  
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) 167,016 210,330 192,978  
Shares authorized under stock option plans, exercise price range, lower range limit (in USD per share) $ 2.32 $ 2.19 $ 2.00  
Shares authorized under stock option plans, exercise price range, upper range limit (in USD per share) $ 3.00 $ 2.38 $ 3.67  
Issuance of common stock $ 420 $ 481 $ 545  
Plan 1999        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) 4,286,114      
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) 16,317,111      
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
Employees and Director Option        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Options, grants in period, weighted average grant date fair value (in USD per share)   $ 1.07 $ 2.79  
Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period 4 years