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Stockholders' Equity - Share Count and Par Value Data Related to Stockholders' Equity (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Equity [Abstract]        
Preferred stock, par value per share $ 0.01us-gaap_PreferredStockParOrStatedValuePerShare $ 0.01us-gaap_PreferredStockParOrStatedValuePerShare    
Preferred stock, shares authorized 10,000,000us-gaap_PreferredStockSharesAuthorized 10,000,000us-gaap_PreferredStockSharesAuthorized    
Preferred stock, shares outstanding 0us-gaap_PreferredStockSharesOutstanding 0us-gaap_PreferredStockSharesOutstanding    
Common stock - class A, par value per share $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare    
Common stock - class A, shares authorized 150,000,000us-gaap_CommonStockSharesAuthorized 150,000,000us-gaap_CommonStockSharesAuthorized    
Common stock - class A, shares issued 72,151,857us-gaap_CommonStockSharesIssued 72,151,857us-gaap_CommonStockSharesIssued    
Common stock - class A, shares outstanding 51,654,337us-gaap_CommonStockSharesOutstanding 50,349,546us-gaap_CommonStockSharesOutstanding 50,908,267us-gaap_CommonStockSharesOutstanding 52,095,166us-gaap_CommonStockSharesOutstanding
Treasury stock, shares held 20,497,520us-gaap_TreasuryStockShares 21,802,311us-gaap_TreasuryStockShares