Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.5.0.2
Share-Based Compensation - Activity (Details) - USD ($)
6 Months Ended
Feb. 22, 2016
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Unrecognized share-based compensation expense        
Restricted stock awards, Unrecognized compensation expense   $ 14,915,000    
Stock options, Unrecognized compensation expense   5,929,000    
Total unrecognized compensation expense related to unvested awards   $ 20,844,000    
Restricted Stock Awards        
Restricted Stock Awards, Number of Shares        
Balance at beginning of period (in shares)   586,600    
Granted (in shares)   325,800    
Converted/Exercised (in shares)   (154,200)    
Forfeited (in shares)   (23,600)    
Balance at end of period (in shares)   734,600    
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share        
Balance at beginning of period (in dollars per share)   $ 21.97    
Granted (in dollars per share)   28.58    
Converted/Exercised (in dollars per share)   19.21    
Forfeited (in dollars per share)   25.70    
Balance at end of period (in dollars per share)   $ 25.36    
Unrecognized share-based compensation expense        
Restricted stock awards, Weighted average remaining vesting period   1 year 10 months 24 days    
Assumptions used to estimate the fair values of the awards granted:        
Remaining measurement period   2 years 10 months 10 days    
Risk free interest rate (as a percent)   0.90%    
Dividend yield (as a percent)   0.00%    
Estimated fair value of awards granted (in dollars per share)   $ 33.77    
Stock Options        
Stock Options, Number of Shares        
Balance at beginning of period (in shares)   387,600    
Granted (in shares)   409,300    
Exercised (in shares)   (3,700)    
Forfeited (in shares)   (34,900)    
Balance at end of period (in shares)   758,300    
Stock Options, Weighted Average Grant Date Fair Value Per Share        
Balance at beginning of period (in dollars per share)   $ 9.35    
Granted (in dollars per share)   10.20    
Converted/Exercised (in dollars per share)   10.35    
Forfeited (in dollars per share)   10.28    
Balance at end of period (in dollars per share)   9.76    
Stock Options, Weighted Average Exercise Price Per Share        
Balance at beginning of period (in dollars per share)   24.03    
Granted (in dollars per share)   26.30    
Exercised (in dollars per share)   26.81    
Forfeited (in dollars per share)   26.58    
Balance at end of period (in dollars per share)   $ 25.13    
Stock options, additional disclosures        
Aggregate intrinsic value   $ 8,397,200   $ 2,611,700
Exercisable, Number of shares   71,700    
Exercisable, Weighted Average Grant Date Fair Value Per Share   $ 6.69    
Exercisable Weighted Average Exercise Price Per Share   $ 16.86    
Exercisable, Aggregate Intrinsic Value   $ 1,387,300    
Unrecognized share-based compensation expense        
Stock options, Weighted average remaining vesting period   2 years    
Stock options, Weighted average remaining contractual life   9 years 1 month 6 days    
Assumptions used to estimate the fair values of the awards granted:        
Risk free interest rate (as a percent)   1.51% 1.82%  
Expected volatility (as a percent)   38.00% 37.00%  
Expected life (in years)   6 years 6 years  
Dividend yield (as a percent)   0.00% 0.00%  
Estimated fair value of awards granted (in dollars per share)   $ 10.20 $ 10.44  
Performance-based conditions | Restricted Stock Awards        
Restricted stock awards, additional disclosures        
Grant date fair value $ 2,275,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-25%        
Restricted stock awards, additional disclosures        
Related expenses 569,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-100%        
Restricted stock awards, additional disclosures        
Related expenses 2,275,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-200%        
Restricted stock awards, additional disclosures        
Related expenses $ 4,550,000