Annual report pursuant to Section 13 and 15(d)

Stock Compensation - Additional Information (Detail)

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Stock Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Apr. 17, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Recognized compensation expense $ 41,100 $ 30,500 $ 28,900  
Excess tax benefits recorded in earnings 300 1,600 2,600  
Unrecognized compensation cost related to nonvested common shares $ 81,300      
Weighted average period for recognition of cost 2 years 1 month 6 days      
Total fair value of shares vested $ 36,300 22,300    
Proceeds from issuance of common stock under the employee stock purchase plan $ 6,173 $ 5,297 $ 5,479  
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period of shares from the date of grant 1 year      
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period of shares from the date of grant 4 years      
Class A Common Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Proceeds from issuance of common stock under the employee stock purchase plan, Shares 261,000 222,000 240,000  
2017 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares that remain available for grant 6,515,750      
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%      
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
2018 ESPP and 2008 ESPP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Proceeds from issuance of common stock under the employee stock purchase plan, Shares 260,630 221,889 240,000  
Proceeds from issuance of common stock under the employee stock purchase plan $ 6,200 $ 5,300 $ 5,500