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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, 2016
Sep. 30, 2015
Dec. 31, 2015
Option      
Summary of activity related to our stock      
Outstanding at the beginning of the period (in shares) 3,163,125    
Stock options granted (in shares) 142,654 729,900.0  
Exercised (in shares) (1,110,193)    
Forfeited (in shares) (115,539)    
Outstanding at the end of the period (in shares) 2,080,047   3,163,125
Exercisable at the end of the period (in shares) 1,274,537    
Weighted average exercise price      
Outstanding at the beginning of the period (in usd per share) $ 20.13    
Weighted average exercise price of stock options granted (in usd per share) 29.22 $ 23.19  
Exercised (in usd per share) 9.57    
Forfeited (in usd per share) 36.53    
Outstanding at the end of the period (in usd per share) 25.48   $ 20.13
Exercisable at the end of the period (in usd per share) $ 20.17    
Weighted average contractual term      
Weighted average contractual term 5 years 6 months 18 days   4 years 11 months 9 days
Exercisable at the end of the period 3 years 7 months 13 days    
Aggregate intrinsic value      
Aggregate intrinsic value, beginning balance (in dollars) $ 35,842    
Aggregate intrinsic value, ending balance (in dollars) 22,595   $ 35,842
Exercisable at the end of the period (in dollars) $ 18,372    
Black Scholes | Minimum      
Aggregate intrinsic value      
Risk-free interest rate (%) 1.25% 1.50%  
Expected stock price volatility (%) 59.75% 55.06%  
Expected option life (in years) 6 years 6 years  
Fair value $ 11.15 $ 10.01  
Black Scholes | Maximum      
Aggregate intrinsic value      
Risk-free interest rate (%) 1.89% 1.78%  
Expected stock price volatility (%) 62.14% 58.58%  
Expected option life (in years) 6 years 3 months 6 years 3 months  
Fair value $ 18.60 $ 17.34  
Binomial | Minimum      
Aggregate intrinsic value      
Risk-free interest rate (%) 0.23% 0.02%  
Expected stock price volatility (%) 59.76% 55.06%  
Expected option life (in years) 4 years 6 months 15 days 4 years 1 month 6 days  
Fair value $ 11.06 $ 9.91  
Binomial | Maximum      
Aggregate intrinsic value      
Risk-free interest rate (%) 1.97% 2.26%  
Expected stock price volatility (%) 62.14% 57.60%  
Expected option life (in years) 4 years 10 months 17 days 4 years 10 months 17 days  
Fair value $ 19.27 $ 16.13