Quarterly report pursuant to Section 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) - $ / shares
 9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Sep. 30, 2014
Dec. 31, 2013
Class Of Stock [Line Items]        
Preferred stock, par value $ 0.01 $ 0.01    
Class A Common Stock        
Class Of Stock [Line Items]        
Common stock, par value $ 0.01 $ 0.01    
Common stock, voting rights 1 vote per share      
Common stockholders rights percentage 100.00%      
Common stock, shares outstanding 7,912,633 7,768,010 7,658,000 7,523,000
Class B Common Stock        
Class Of Stock [Line Items]        
Common stock, par value $ 0.01 $ 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 4,772,130 4,520,413 4,570,000 4,465,000
Deferred equity units exercisable 4,911      
Restricted stock units granted 966,510