Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Details)

v3.8.0.1
Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock Based Compensation        
Allocated Share-based Compensation Expense   $ 5,292 $ 5,713 $ 6,380
Options        
Common Stock, Capital Shares Reserved for Future Issuance 2,800,000 2,800,000    
Series A common stock        
Options        
Common Stock, Capital Shares Reserved for Future Issuance 404,000 404,000    
Series C common stock        
Options        
Common Stock, Capital Shares Reserved for Future Issuance 2,400,000 2,400,000    
2014 Plan        
Stock Based Compensation        
Number of authorized shares 8,400,000 8,400,000    
Fair value assumptions        
Dividend rate   0.00% 0.00% 0.00%
2014 Plan | Awards        
Options        
Unrecognized compensation cost options $ 10,000 $ 10,000    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition   1 year 6 months    
2014 Plan | Awards | Series A common stock        
Options        
Outstanding beginning balance (in shares)   454,000    
Exercised (in shares)   (50,000)    
Outstanding ending balance (in shares) 404,000 404,000 454,000  
Number of awards exercisable (in shares) 402,000 402,000    
WAEP Outstanding beginning balance (in dollars per share)   $ 32.47    
WAEP options exercised (in dollars per share)   26.85    
WAEP Outstanding ending balance (in dollars per share) $ 33.16 33.16 $ 32.47  
WAEP options exercisable (in dollars per share) $ 33.08 $ 33.08    
Weighted average remaining contractual life outstanding 2 years      
Weighted average remaining contractual life exercisable 2 years      
Aggregate intrinsic value outstanding $ 21,000 $ 21,000    
Aggregate intrinsic value exercisable $ 21,000 $ 21,000    
2014 Plan | Awards | Series C common stock        
Options        
Outstanding beginning balance (in shares)   2,467,000    
Options granted (in shares)   16,000    
Exercised (in shares)   (95,000)    
Outstanding ending balance (in shares) 2,388,000 2,388,000 2,467,000  
Number of awards exercisable (in shares) 866,000 866,000    
WAEP Outstanding beginning balance (in dollars per share)   $ 42.45    
WAEP Options granted (in dollars per share)   85.34    
WAEP options exercised (in dollars per share)   27.08    
WAEP Outstanding ending balance (in dollars per share) $ 43.35 43.35 $ 42.45  
WAEP options exercisable (in dollars per share) $ 34.34 $ 34.34    
Weighted average remaining contractual life outstanding 5 years 2 months 12 days      
Weighted average remaining contractual life exercisable 2 years 1 month 6 days      
Aggregate intrinsic value outstanding $ 100,000 $ 100,000    
Aggregate intrinsic value exercisable $ 44,000 44,000    
2014 Plan | Options        
Options        
Aggregate intrinsic value exercises   $ 8,100 $ 14,400 $ 11,200
2014 Plan | Options | Series A common stock        
Options        
Options granted (in shares)   0 0 0
2014 Plan | Options | Series B common stock        
Options        
Outstanding ending balance (in shares) 0 0    
2014 Plan | Options | Series C common stock        
Stock Based Compensation        
Vesting period   1 year    
Weighted average grant date fair value (in dollars per share) $ 22.68 $ 22.68 $ 18.64 $ 13.51
Options        
Options granted (in shares)   16,000 17,000 21,000
2014 Plan | Minimum        
Stock Based Compensation        
Vesting period   1 year    
Term of awards   7 years    
2014 Plan | Minimum | Options        
Stock Based Compensation        
Term of awards   4 years 7 months 6 days 4 years 7 months 6 days 4 years 7 months 6 days
Fair value assumptions        
Volatility rate   24.40% 24.40% 24.40%
2014 Plan | Maximum        
Stock Based Compensation        
Vesting period   5 years    
Term of awards   10 years    
2014 Plan | Maximum | Options        
Stock Based Compensation        
Term of awards   5 years 3 months 18 days 5 years 3 months 18 days 5 years 3 months 18 days
Fair value assumptions        
Volatility rate   28.20% 28.20% 28.20%
Operating expense        
Stock Based Compensation        
Allocated Share-based Compensation Expense   $ (2)   $ 7
Selling, general and administrative        
Stock Based Compensation        
Allocated Share-based Compensation Expense   5,114 $ 5,555 5,978
Research and development        
Stock Based Compensation        
Allocated Share-based Compensation Expense   $ 180 $ 158 $ 395