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Stock Repurchase Program - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 28, 2011
Mar. 31, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Stock Repurchase Program [Line Items]          
Common stock repurchase authorized amount $ 100,000,000        
Total stock repurchased, shares   3,996,118      
Common stock repurchased and retired, shares   35,563      
Common stock repurchased and retired, value   1,000,000 45,162,000 123,077,000 40,851,000
Common stock repurchase price per share   $ 29.40      
Stock Repurchase Program Additional Authorization
          
Stock Repurchase Program [Line Items]          
Common stock repurchase authorized amount       150,000,000  
Common stock repurchased and retired, shares     1,472,096    
Common stock repurchased and retired, value     44,100,000    
Common stock repurchase price per share     $ 29.97    
Common stock repurchase authorization amount available     $ 105,900,000