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Earnings Per Common Share - Additional Information (Detail)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Earnings Per Share [Abstract]        
Shares excluded from calculation of diluted earnings per share 1.2 1.8 1.5 1.6