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Share-Based Compensation - Share-Based Payment Award Activity (Parenthetical) (Detail) (USD $)
Sep. 30, 2013
Jun. 30, 2013
Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Intrinsic value represents the excess of the closing stock price related to options outstanding $ 16.57 $ 17.67 $ 13.59