Quarterly report pursuant to Section 13 or 15(d)

Stock Compensation - Additional Information (Detail)

v3.7.0.1
Stock Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Apr. 17, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation expense $ 7.6 $ 6.2 $ 14.2 $ 10.9  
Unrecognized compensation cost related to nonvested common shares 50.1   $ 50.1    
Weighted average period for recognition of cost     2 years 2 months 12 days    
ASU 2016-09 [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Tax (expense) benefit recorded $ (0.3)   $ 0.9    
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