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Equity-based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Jan. 01, 2021
Jun. 30, 2019
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2013
Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Stock option granted     28,250   140,569      
Weighted average grant date fair value of options granted     $ 29.13   $ 21.15      
Tax benefits in relation to equity-based compensation     $ 2.2 $ 3.4 $ 15.7 $ 5.1    
General and Administrative Expense                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Equity-based compensation cost     $ 1.4 $ 1.0 $ 3.7 $ 2.4    
Class A Common Stock | Restricted Stock Units (RSUs)                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Restricted stock unit granted     0   28,224      
Weighted average grant date fair value of RSUs granted [1]         $ 48.16      
2013 Equity Incentive Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Equity incentive plans award term             10-year  
Equity incentive plans vesting period             5 years  
2013 Equity Incentive Plan | Stock Option                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Total unrecognized compensation cost     $ 11.9   $ 11.9      
Total unrecognized compensation cost to be recognized, weighted average service period         3 years 2 months 12 days      
Amendment to 2013 Equity Incentive Plan | Class A Common Stock | Maximum                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Number of shares available for issuance               6,207,978
2019 Equity Incentive Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Common stock reserved for issuance     4,900,000   4,900,000      
Increase in number of shares reserved for future issuance, description         The number of shares that will be available for issuance under our 2019 Plan also will increase annually on the first day of each year beginning in 2020, in an amount equal to the least of: (a) 6,900,000 shares, (b) 5% of the outstanding shares of all classes of our common stock as of the last day of the immediately preceding year and (c) such other amount as our board of directors may determine      
Increase in number of shares reserved for future issuance, shares 2,000,000.0 6,900,000            
Percentage of number of shares of common stock outstanding   5.00%            
2019 Equity Incentive Plan | Restricted Stock Units (RSUs)                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Total unrecognized compensation cost     $ 11.9   $ 11.9      
Total unrecognized compensation cost to be recognized, weighted average service period         3 years 2 months 12 days      
2019 Equity Incentive Plan | Class A Common Stock                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Common stock reserved for issuance   4,500,000            
2019 Equity Incentive Plan | Class A Common Stock | Restricted Stock Units (RSUs)                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Restricted stock unit granted [1]         28,224      
[1] Includes an adjustment of 11,763 shares underlying performance-based RSU awards made during the nine months ended September 30, 2021. The vesting of such RSUs is based upon the Company’s current performance against predefined financial targets.