Quarterly report pursuant to sections 13 or 15(d)

Stockholders' Equity - Summary of Authorized and Outstanding Equity (Parenthetical) (Detail)

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Stockholders' Equity - Summary of Authorized and Outstanding Equity (Parenthetical) (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Sep. 30, 2012
Dec. 31, 2011
Schedule Of Stockholders Equity [Line Items]        
Preferred stock, par value $ 0.01      
Class A Common Stock
        
Schedule Of Stockholders Equity [Line Items]        
Common stock, par value $ 0.01      
Common stock voting rights 1 vote per share      
Common stockholders rights percentage 100.00%      
Common stock, shares outstanding 5,509,297 0 0 0
Class B Common Stock
        
Schedule Of Stockholders Equity [Line Items]        
Common stock, par value $ 0.01      
Common stock voting rights 1 vote per share      
Class of share exchangeable to another class One share of Class A common stock      
Common stock, shares outstanding 6,461,764 0 0 0
Deferred equity units exercisable 191,828