Quarterly report pursuant to Section 13 or 15(d)

Share Repurchase Program - Additional Information (Detail)

v3.10.0.1
Share Repurchase Program - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
9 Months Ended
Sep. 30, 2018
Feb. 06, 2018
Dec. 31, 2017
Class of Stock [Line Items]      
Stock repurchase program expiration date Feb. 06, 2021    
Class A Common Stock [Member]      
Class of Stock [Line Items]      
Common Stock, par value $ 0.001   $ 0.001
Stock repurchase program authorized amount   $ 150.0  
Class A Common Stock [Member] | Share Repurchase Program [Member]      
Class of Stock [Line Items]      
Common Stock, par value   $ 0.001  
Stock repurchase program remaining authorized repurchase amount $ 92.0