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Earnings Per Common Share - Additional Information (Detail) (USD $)
9 Months Ended
Sep. 30, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]  
Conversion price of Convertible Notes, per share 31.25
3 3/4% Senior Subordinated Convertible Notes Due 2012
 
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]  
Convertible notes maturity date Jul. 15, 2012
Senior subordinated convertible notes, interest percentage 3.75%