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SHAREHOLDERS’ EQUITY AND SHARE-BASED COMPENSATION Black-Scholes and Binomial model Assumptions and Summary of Activity related to our stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Stock options      
Summary of activity related to our stock      
Outstanding at the beginning of the period (in shares) 1,996,509    
Granted (in shares) 216,430 143,000  
Exercised (in shares) (192,378)    
Forfeited (in shares) (222,920)    
Outstanding at the end of the period (in shares) 1,797,641   1,996,509
Exercisable at the end of the period (in shares) 1,170,148    
Weighted average exercise price      
Outstanding at the beginning of the period (in usd per share) $ 25.98    
Weighted average exercise price of stock options granted (in usd per share) 34.07 $ 29.22  
Exercised (in usd per share) 10.83    
Forfeited (in usd per share) 31.21    
Outstanding at the end of the period (in usd per share) 27.93   $ 25.98
Exercisable at the end of the period (in usd per share) $ 22.56    
Weighted average contractual term      
Weighted average contractual term 5 years 1 month 21 days   5 years 3 months 26 days
Exercisable at the end of the period 3 years 5 months 23 days    
Aggregate intrinsic value      
Aggregate intrinsic value, beginning balance (in dollars) $ 15,942    
Aggregate intrinsic value, ending balance (in dollars) 8,413   $ 15,942
Exercisable at the end of the period (in dollars) $ 7,723    
Black Scholes | Minimum      
Aggregate intrinsic value      
Risk-free interest rate (%) 1.89% 1.25%  
Expected stock price volatility (%) 61.49% 59.75%  
Expected dividend yield 0.00% 0.00%  
Expected option life (in years) 6 years 6 years  
Fair value (in usd per share) $ 13.57 $ 11.15  
Black Scholes | Maximum      
Aggregate intrinsic value      
Risk-free interest rate (%) 2.29% 1.89%  
Expected stock price volatility (%) 71.31% 62.14%  
Expected dividend yield 0.00% 0.00%  
Expected option life (in years) 7 years 6 months 6 years 3 months  
Fair value (in usd per share) $ 24.80 $ 18.60  
Binomial | Minimum      
Aggregate intrinsic value      
Risk-free interest rate (%) 0.77% 0.23%  
Expected stock price volatility (%) 66.68% 59.76%  
Expected dividend yield 0.00% 0.00%  
Expected option life (in years) 2 years 6 months 18 days 4 years 6 months 15 days  
Fair value (in usd per share) $ 11.94 $ 11.06  
Binomial | Maximum      
Aggregate intrinsic value      
Risk-free interest rate (%) 2.38% 1.97%  
Expected stock price volatility (%) 71.31% 62.14%  
Expected dividend yield 0.00% 0.00%  
Expected option life (in years) 4 years 3 months 26 days 4 years 10 months 17 days  
Fair value (in usd per share) $ 24.30 $ 19.27