Annual report pursuant to Section 13 and 15(d)

Stock Compensation - Additional Information (Detail)

v3.10.0.1
Stock Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Apr. 17, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Recognized compensation expense $ 30,500 $ 28,900 $ 23,100  
Income tax benefits recorded in additional paid-in capital     4,682  
Excess tax benefits recorded in earnings 1,600 2,600    
Unrecognized compensation cost related to nonvested common shares $ 76,000      
Weighted average period for recognition of cost 2 years 7 months 6 days      
Total fair value of shares vested $ 22,300 24,000    
Proceeds from issuance of common stock under the employee stock purchase plan $ 5,297 $ 5,479 $ 5,120  
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 222,000 240,000 221,000  
2017 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares that remain available for grant 8,090,500      
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 221,889 240,000 220,844  
Proceeds from issuance of common stock under the employee stock purchase plan $ 5,300 $ 5,500 $ 5,100