Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.8.0.1
Share-Based Compensation - Activity (Details) - USD ($)
9 Months Ended
Feb. 21, 2017
Feb. 22, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Stock options, additional disclosures          
Weighted average remaining contractual term for vested stock options     8 years 1 month 6 days    
Unrecognized share-based compensation expense          
Restricted stock awards, Unrecognized compensation expense     $ 12,346,000    
Stock options, Unrecognized compensation expense     4,724,000    
Total unrecognized compensation expense related to unvested awards     $ 17,070,000    
Restricted Stock Awards          
Restricted Stock Awards, Number of Shares          
Balance at beginning of period (in shares)     653,100    
Granted (in shares)     158,900    
Converted/Exercised (in shares)     (183,100)    
Forfeited (in shares)     (33,000)    
Balance at end of period (in shares)     595,900    
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share          
Balance at beginning of period (in dollars per share)     $ 25.71    
Granted (in dollars per share)     44.28    
Converted/Exercised (in dollars per share)     23.91    
Forfeited (in dollars per share)     31.18    
Balance at end of period (in dollars per share)     $ 30.91    
Unrecognized share-based compensation expense          
Restricted stock awards, Weighted average remaining vesting period     1 year 6 months    
Assumptions used to estimate the fair values of the awards granted:          
Remaining measurement period     2 years 10 months 10 days 2 years 10 months 10 days  
Risk free interest rate (as a percent)     1.46% 0.90%  
Dividend yield (as a percent)     0.00% 0.00%  
Estimated fair value of awards granted (in dollars per share)     $ 50.06 $ 33.77  
Stock Options          
Stock Options, Number of Shares          
Balance at beginning of period (in shares)     712,000    
Granted (in shares)     153,000    
Exercised (in shares)     (160,700)    
Balance at end of period (in shares)     704,300    
Stock Options, Weighted Average Grant Date Fair Value Per Share          
Balance at beginning of period (in dollars per share)     $ 9.73    
Granted (in dollars per share)     14.62    
Converted/Exercised (in dollars per share)     8.34    
Balance at end of period (in dollars per share)     11.11    
Stock Options, Weighted Average Exercise Price Per Share          
Balance at beginning of period (in dollars per share)     25.03    
Granted (in dollars per share)     38.89    
Exercised (in dollars per share)     21.26    
Balance at end of period (in dollars per share)     $ 28.90    
Stock options, additional disclosures          
Aggregate intrinsic value     $ 23,045,200   $ 7,525,800
Converted/Exercised aggregate intrinsic value     $ 5,500,800    
Exercisable, Number of shares     162,200    
Exercisable, Weighted Average Grant Date Fair Value Per Share     $ 10.23    
Exercisable Weighted Average Exercise Price Per Share     $ 26.48    
Exercisable, Aggregate Intrinsic Value     $ 5,700,100    
Unrecognized share-based compensation expense          
Stock options, Weighted average remaining vesting period     1 year 6 months    
Assumptions used to estimate the fair values of the awards granted:          
Risk free interest rate (as a percent)     2.18% 1.51%  
Expected volatility using historical return volatility and implied volatility (as a percent)     35.00% 38.00%  
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)     $ 14.44 $ 10.20  
Performance-based conditions | Restricted Stock Awards          
Restricted stock awards, additional disclosures          
Grant date fair value $ 2,143,000 $ 1,988,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-25%          
Restricted stock awards, additional disclosures          
Related expenses 536,000 497,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-100%          
Restricted stock awards, additional disclosures          
Related expenses 2,143,000 1,988,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-200%          
Restricted stock awards, additional disclosures          
Related expenses $ 4,286,000 $ 3,976,000