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Net Income Per Common Share - Average Exercise Prices of Options Excluded from Computation of Diluted Net Income Per Common Share (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Abstract]        
Shares 466,159 607,200 475,867 607,200
Average Exercise Price $ 39.76 $ 38.70 $ 39.69 $ 38.70