Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Activity (Details)

v3.21.2
Share-Based Compensation - Activity (Details) - USD ($)
3 Months Ended 9 Months Ended
Feb. 16, 2021
Feb. 17, 2020
Feb. 18, 2019
Mar. 31, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Stock Options, Number of Shares                
Converted/Exercised (in shares)       (51,915) (19,242)      
Stock options, additional disclosures                
Weighted average remaining contractual term for vested stock options           6 years    
Unrecognized share-based compensation expense                
Restricted stock awards, Unrecognized compensation expense           $ 10,196,000    
Restricted stock awards, Weighted average remaining vesting period           1 year    
Stock options, Unrecognized compensation expense           $ 1,639,000    
Stock options, Weighted average remaining vesting period           1 year 1 month 6 days    
Total unrecognized compensation expense related to unvested awards           $ 11,835,000    
Restricted Stock Awards                
Restricted Stock Awards, Number of Shares                
Balance at beginning of period (in shares)       324,800   324,800    
Granted (in shares)           61,000.0    
Converted/Exercised (in shares)           (143,600)    
Forfeited/Expired (in shares)           (9,000.0)    
Balance at end of period (in shares)           233,200    
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share                
Balance at beginning of period (in dollars per share)       $ 87.79   $ 87.79    
Granted (in dollars per share)           245.67    
Converted/Exercised (in dollars per share)           81.34    
Forfeited/Expired (in dollars per share)           89.62    
Balance at end of period (in dollars per share)           $ 113.52    
Assumptions used to estimate the fair values of the awards granted:                
Measurement period (years)           2 years 10 months 13 days 2 years 10 months 17 days  
Risk free interest rate (as a percent)           0.22% 1.40%  
Dividend yield (as a percent)           0.00% 0.00%  
Estimated fair value of market-based RSAs at grant date (in dollars per share)           $ 298.66 $ 158.24  
Restricted Stock Awards | Performance-based conditions                
Restricted stock awards, additional disclosures                
Grant date fair value $ 2,564,000 $ 2,687,000 $ 2,196,000          
Restricted Stock Awards | Performance-based conditions | Payout Range-0%                
Restricted stock awards, additional disclosures                
Payout range (as a percent) 0.00% 0.00% 0.00%          
Restricted Stock Awards | Performance-based conditions | Payout Range-25%                
Restricted stock awards, additional disclosures                
Payout range (as a percent) 25.00% 25.00% 25.00%          
Related expenses $ 641,000 $ 672,000 $ 549,000          
Restricted Stock Awards | Performance-based conditions | Payout Range-100%                
Restricted stock awards, additional disclosures                
Payout range (as a percent) 100.00% 100.00% 100.00%          
Related expenses $ 2,564,000 $ 2,687,000 $ 2,196,000          
Restricted Stock Awards | Performance-based conditions | Payout Range-200%                
Restricted stock awards, additional disclosures                
Payout range (as a percent) 200.00% 200.00% 200.00%          
Related expenses $ 5,128,000 $ 5,374,000 $ 4,392,000          
RSAs granted February 19, 2018 | Performance-based conditions                
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       $ 3,700,000        
Stock Options                
Stock Options, Number of Shares                
Balance at beginning of period (in shares)       239,700   239,700    
Granted (in shares)           24,100    
Converted/Exercised (in shares)           (51,900)    
Balance at end of period (in shares)           211,900    
Stock Options, Weighted Average Grant Date Fair Value Per Share                
Balance at beginning of period (in dollars per share)       $ 24.33   $ 24.33    
Granted (in dollars per share)           89.59    
Converted/Exercised (in dollars per share)           21.97    
Balance at end of period (in dollars per share)           32.33    
Stock Options, Weighted Average Exercise Price Per Share                
Balance at beginning of period (in dollars per share)       $ 68.86   68.86    
Granted (in dollars per share)           214.58    
Converted/Exercised (in dollars per share)           61.30    
Balance at end of period (in dollars per share)           $ 87.28    
Stock options, additional disclosures                
Aggregate intrinsic value           $ 25,129,700   $ 27,612,100
Converted/Exercised aggregate intrinsic value           $ 7,039,900    
Exercisable, Number of shares           115,700    
Exercisable, Weighted Average Grant Date Fair Value Per Share           $ 20.97    
Exercisable Weighted Average Exercise Price Per Share           $ 57.86    
Exercisable, Aggregate Intrinsic Value           $ 17,000,800    
Assumptions used to estimate the fair values of the awards granted:                
Risk free interest rate (as a percent)           0.76% 1.53%  
Expected volatility using historical return volatility and implied volatility (as a percent)           43.29% 31.50%  
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)           $ 89.59 $ 39.49