Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.4.0.3
Share-Based Compensation - Activity (Details) - USD ($)
3 Months Ended
Feb. 22, 2016
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Restricted Stock Awards        
Restricted Stock Awards, Number of Shares        
Balance at beginning of period (in shares)   586,600    
Granted (in shares)   317,200    
Converted/Exercised (in shares)   (152,100)    
Forfeited (in shares)   (1,200)    
Balance at end of period (in shares)   750,500    
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)   28.41    
Converted/Exercised (in dollars per share)   19.16    
Forfeited (in dollars per share)   23.20    
Balance at end of period (in dollars per share)   $ 25.25    
Restricted stock awards, additional disclosures        
Unrecognized compensation expense related to unvested restricted stock awards   $ 16,800,000    
Weighted average remaining vesting period   2 years 2 months 12 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    
Balance at end of period (in shares)   796,900    
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    
Balance at end of period (in dollars per share)   9.79    
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    
Balance at end of period (in dollars per share)   $ 25.20    
Stock options, additional disclosures        
Aggregate intrinsic value   $ 3,620,400   $ 2,611,700
Unrecognized compensation expense related to unvested stock options   $ 6,800,000    
Weighted average remaining vesting period   2 years 3 months 18 days    
Weighted average remaining contractual life   9 years 4 months 24 days    
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   $ 923,900    
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 $ 2,351,700      
Performance-based conditions | Restricted Stock Awards | Payout Range-0%        
Restricted stock awards, additional disclosures        
Payout range (as a percent) 0.00%      
Performance-based conditions | Restricted Stock Awards | Payout Range-25%        
Restricted stock awards, additional disclosures        
Payout range (as a percent) 25.00%      
Related expenses $ 587,900      
Performance-based conditions | Restricted Stock Awards | Payout Range-100%        
Restricted stock awards, additional disclosures        
Payout range (as a percent) 100.00%      
Related expenses $ 2,351,700      
Performance-based conditions | Restricted Stock Awards | Payout Range-200%        
Restricted stock awards, additional disclosures        
Payout range (as a percent) 200.00%      
Related expenses $ 4,703,400