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Stock Repurchase Program - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2011
Stock Repurchase Program [Line Items]    
Common stock repurchase authorized amount   $ 150.0
Common stock repurchased, shares 121,263  
Common stock repurchased, value 5.1  
Common stock repurchase price per share $ 42.47  
Common stock repurchase authorization amount available $ 100.7