Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.19.2
Share-Based Compensation - Activity (Details) - USD ($)
6 Months Ended
Feb. 18, 2019
Feb. 19, 2018
Feb. 21, 2017
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Unrecognized share-based compensation expense            
Restricted stock awards, Unrecognized compensation expense       $ 12,319,000    
Restricted stock awards, Weighted average remaining vesting period       1 year 4 months 24 days    
Stock options, Unrecognized compensation expense       $ 2,845,000    
Stock options, Weighted average remaining vesting period       1 year 1 month 6 days    
Total unrecognized compensation expense related to unvested awards       $ 15,164,000    
Restricted Stock Awards            
Restricted Stock Awards, Number of Shares            
Balance at beginning of period (in shares)       499,200    
Granted (in shares)       227,100    
Converted/Exercised (in shares)       (291,400)    
Forfeited (in shares)       (17,400)    
Balance at end of period (in shares)       417,500    
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share            
Balance at beginning of period (in dollars per share)       $ 41.29    
Granted (in dollars per share)       67.37    
Converted/Exercised (in dollars per share)       31.23    
Forfeited (in dollars per share)       56.29    
Balance at end of period (in dollars per share)       $ 55.97    
Assumptions used to estimate the fair values of the awards granted:            
Measurement period (years)       2 years 10 months 13 days 2 years 10 months 13 days  
Risk free interest rate (as a percent)       2.50% 2.36%  
Dividend yield (as a percent)       0.00% 0.00%  
Estimated fair value of awards granted (in dollars per share)       $ 80.74 $ 103.31  
Stock Options            
Stock Options, Number of Shares            
Balance at beginning of period (in shares)       611,400    
Granted (in shares)       103,500    
Converted/Exercised (in shares)       (183,500)    
Forfeited (in shares)       (9,700)    
Expired (in shares)       (2,700)    
Balance at end of period (in shares)       519,000.0    
Stock Options, Weighted Average Grant Date Fair Value Per Share            
Balance at beginning of period (in dollars per share)       $ 13.10    
Granted (in dollars per share)       21.16    
Converted/Exercised (in dollars per share)       10.53    
Forfeited (in dollars per share)       $ 20.28    
Expired (in dollars per share)       14.44    
Balance at end of period (in dollars per share)       $ 15.47    
Stock Options, Weighted Average Exercise Price Per Share            
Balance at beginning of period (in dollars per share)       34.45    
Granted (in dollars per share)       58.08    
Converted/Exercised (in dollars per share)       27.18    
Forfeited (in dollars per share)       54.62    
Expired (in dollars per share)       38.39    
Balance at end of period (in dollars per share)       $ 41.34    
Stock options, additional disclosures            
Aggregate intrinsic value       $ 21,500,400   $ 8,685,800
Converted/Exercised aggregate intrinsic value       $ 8,824,000.0    
Exercisable, Number of shares       183,000.0    
Exercisable, Weighted Average Grant Date Fair Value Per Share       $ 13.48    
Exercisable Weighted Average Exercise Price Per Share       $ 35.52    
Exercisable, Aggregate Intrinsic Value       $ 8,645,800    
Weighted average remaining contractual term for vested stock options       7 years    
Assumptions used to estimate the fair values of the awards granted:            
Risk free interest rate (as a percent)       2.59% 2.78%  
Expected volatility using historical return volatility and implied volatility (as a percent)       32.50% 32.50%  
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)       $ 21.16 $ 27.44  
Performance-based conditions | Restricted Stock Awards            
Restricted stock awards, additional disclosures            
Grant date fair value $ 2,533,000 $ 2,102,000 $ 1,839,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-0%            
Restricted stock awards, additional disclosures            
Payout range (as a percent) 0.00% 0.00% 0.00%      
Performance-based conditions | Restricted Stock Awards | Payout Range-25%            
Restricted stock awards, additional disclosures            
Payout range (as a percent) 25.00% 25.00% 25.00%      
Related expenses $ 633,000 $ 526,000 $ 460,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-100%            
Restricted stock awards, additional disclosures            
Payout range (as a percent) 100.00% 100.00% 100.00%      
Related expenses $ 2,533,000 $ 2,102,000 $ 1,839,000      
Performance-based conditions | Restricted Stock Awards | Payout Range-200%            
Restricted stock awards, additional disclosures            
Payout range (as a percent) 200.00% 200.00% 200.00%      
Related expenses $ 5,066,000 $ 4,204,000 $ 3,678,000      
Performance-based conditions | RSAs granted on February 22, 2016            
Restricted stock awards, additional disclosures            
Cumulative period of achievement       3 years    
Cumulative achievement percentage       88.60%    
Total compensation expense recognized over the performance period, net of forfeitures       $ 1,700,000