Quarterly report pursuant to sections 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 9 Months Ended 0 Months Ended 9 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Jul. 12, 2013
Class A Common Stock
Jul. 02, 2013
Class A Common Stock
Sep. 30, 2013
Class A Common Stock
Dec. 31, 2012
Class A Common Stock
Sep. 30, 2012
Class A Common Stock
Dec. 31, 2011
Class A Common Stock
Sep. 30, 2013
Class B Common Stock
Dec. 31, 2012
Class B Common Stock
Sep. 30, 2012
Class B Common Stock
Dec. 31, 2011
Class B Common Stock
Sep. 30, 2013
Class B Common Stock
Employee Stock
Class Of Stock [Line Items]                              
Partnership distributions, amount $ 1,427 $ 1,533 $ 29,327 $ 14,712                      
Amount distributed to existing partners     10,000                        
Distributions of partner incentive allocations of net income 0 0 12,104 8,775                      
Accrued partner incentive allocations $ 3,175                            
Issuance of Class A shares in IPO, Shares         718,603 4,790,684 5,509,000       0        
Common stock shares issued             5,509,297       6,461,764       6,459,316
Common stock shares issued to partner                     16,540        
Stock Redeemed or Called During Period, Shares                     14,092        
Common Stock, shares outstanding             5,509,297 0 0 0 6,461,764 0 0 0