Quarterly report pursuant to Section 13 or 15(d)

Stock Compensation - Additional Information (Detail)

v3.21.2
Stock Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Recognized stock compensation expense $ 14.7 $ 29.7 $ 41.4 $ 55.0
Unrecognized compensation cost related to nonvested common shares $ 78.9   $ 78.9  
Weighted average period for recognition of cost     1 year 10 months 13 days  
Performance-Based Awards [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period     3 years  
Performance-Based Awards [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Payout percentage of performance awards     0.00%  
Performance-Based Awards [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Payout percentage of performance awards     200.00%  
2017 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares that remain available for grant 4,836,249   4,836,249  
2018 ESPP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of price of common stock purchased     85.00%  
Maximum percentage of employee's compensation to purchase common stock 15.00%   15.00%  
2018 ESPP [Member] | Class A Common Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for sale under employee stock purchase plan 5,000,000   5,000,000