Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.20.2
Share-Based Compensation - Activity (Details) - USD ($)
3 Months Ended 9 Months Ended
Feb. 17, 2020
Feb. 18, 2019
Feb. 19, 2018
Sep. 30, 2020
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Stock Options, Number of Shares              
Converted/Exercised (in shares)       (19,242)      
Unrecognized share-based compensation expense              
Restricted stock awards, Unrecognized compensation expense       $ 11,536,000 $ 11,536,000    
Restricted stock awards, Weighted average remaining vesting period         1 year 2 months 12 days    
Stock options, Unrecognized compensation expense       1,359,000 $ 1,359,000    
Stock options, Weighted average remaining vesting period         1 year    
Total unrecognized compensation expense related to unvested awards       $ 12,895,000 $ 12,895,000    
Restricted Stock Awards              
Restricted Stock Awards, Number of Shares              
Balance at beginning of period (in shares)         411,600    
Granted (in shares)         192,800    
Converted/Exercised (in shares)         (251,100)    
Forfeited/Expired (in shares)         (26,100)    
Balance at end of period (in shares)       327,200 327,200    
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share              
Balance at beginning of period (in dollars per share)         $ 57.51    
Granted (in dollars per share)         129.11    
Converted/Exercised (in dollars per share)         43.44    
Forfeited/Expired (in dollars per share)         90.81    
Balance at end of period (in dollars per share)       $ 87.20 $ 87.20    
Assumptions used to estimate the fair values of the awards granted:              
Measurement period (years)         2 years 10 months 17 days 2 years 10 months 13 days  
Risk free interest rate (as a percent)         1.40% 2.50%  
Dividend yield (as a percent)         0.00% 0.00%  
Estimated fair value of market-based RSAs at grant date (in dollars per share)         $ 158.24 $ 80.74  
Stock Options              
Stock Options, Number of Shares              
Balance at beginning of period (in shares)         373,500    
Granted (in shares)         71,000.0    
Converted/Exercised (in shares)         (184,800)    
Forfeited/Expired (in shares)         (20,000.0)    
Balance at end of period (in shares)       239,700 239,700    
Stock Options, Weighted Average Grant Date Fair Value Per Share              
Balance at beginning of period (in dollars per share)         $ 17.06    
Granted (in dollars per share)         39.49    
Converted/Exercised (in dollars per share)         14.84    
Forfeited/Expired (in dollars per share)         30.13    
Balance at end of period (in dollars per share)       $ 24.33 24.33    
Stock Options, Weighted Average Exercise Price Per Share              
Balance at beginning of period (in dollars per share)         45.90    
Granted (in dollars per share)         118.58    
Converted/Exercised (in dollars per share)         39.54    
Forfeited/Expired (in dollars per share)         87.67    
Balance at end of period (in dollars per share)       $ 68.86 $ 68.86    
Stock options, additional disclosures              
Aggregate intrinsic value       $ 22,925,100 $ 22,925,100   $ 21,356,400
Converted/Exercised aggregate intrinsic value         $ 13,222,100    
Exercisable, Number of shares       63,800 63,800    
Exercisable, Weighted Average Grant Date Fair Value Per Share         $ 18.89    
Exercisable Weighted Average Exercise Price Per Share       $ 51.04 $ 51.04    
Exercisable, Aggregate Intrinsic Value       $ 7,638,000.0 $ 7,638,000.0    
Weighted average remaining contractual term for vested stock options         6 years 6 months    
Assumptions used to estimate the fair values of the awards granted:              
Risk free interest rate (as a percent)         1.53% 2.59%  
Expected volatility using historical return volatility and implied volatility (as a percent)         31.50% 32.50%  
Expected life (in years)         6 years 6 years  
Dividend yield (as a percent)         0.00% 0.00%  
Estimated fair value of market-based RSAs at grant date (in dollars per share)         $ 39.49 $ 21.16  
Performance-based conditions | Restricted Stock Awards              
Restricted stock awards, additional disclosures              
Grant date fair value $ 2,716,000 $ 2,281,000 $ 1,865,000        
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 $ 679,000 $ 570,000 $ 466,000        
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 $ 2,716,000 $ 2,281,000 $ 1,865,000        
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 $ 5,432,000 $ 4,562,000 $ 3,730,000        
Performance-based conditions | RSAs granted on February 21, 2017              
Restricted stock awards, additional disclosures              
Cumulative period of achievement         3 years    
Cumulative achievement percentage         200.00%    
Total compensation expense recognized over the performance period, net of forfeitures         $ 3,300,000