Quarterly report pursuant to Section 13 or 15(d)

Stock Compensation - Additional Information (Detail)

v3.19.2
Stock Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Apr. 17, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation expense $ 10,600 $ 7,300 $ 19,500 $ 16,000  
Stock redeemed, value 7,767 $ 2,463 13,583 $ 11,181  
Unrecognized compensation cost related to nonvested common shares $ 101,100   $ 101,100    
Weighted average period for recognition of cost     2 years 6 months    
Class A Common Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock redeemed, shares 248,312 87,326 418,385 300,256  
Stock redeemed, value $ 7,800 $ 2,500 $ 13,600 $ 11,200  
2017 Plan [Member] | Class A Common Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of shares reserved for issuance         10,000,000
2018 ESPP [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Maximum percentage of employee's compensation to purchase common stock 15.00%   15.00%    
Percentage of price of common stock purchased     85.00%    
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