Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Class B Common Stock (Detail)

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Stockholders' Equity - Class B Common Stock (Detail)
 1 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended
Dec. 31, 2012
May 31, 2014
Class B Common Stock
Feb. 28, 2014
Class B Common Stock
Sep. 30, 2014
Class B Common Stock
Sep. 30, 2013
Class B Common Stock
Dec. 31, 2012
Class B Common Stock
Sep. 30, 2014
Class B Common Stock
Resale and Registration Rights Agreement
Sep. 30, 2014
Class B Common Stock
Resale and Registration Rights Agreement
Sep. 30, 2014
Class B Common Stock
May 2014
Class Of Stock [Line Items]                  
Stock repurchased/surrendered and cancelled , transaction date       Feb. 01, 2014         May 01, 2014
Stock issued upon vesting of deferred equity units, transaction date       Feb. 01, 2014          
Common stock exchange date       Sep. 30, 2014          
Balance, Shares        4,464,617 6,462,000         
Common stock repurchased/surrendered and cancelled   (5,893) (16,530) (16,530)         (5,893)
Common stock issued upon vesting of deferred equity units     261,958 261,958          
Exchange of Class B common stock for Class A common stock       (136)     133,739 (133,739)  
Balance, Shares        4,570,413 6,462,000