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Earnings Per Common Share - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]    
Conversion price of convertible notes, per share $ 31.25 $ 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 Jul. 15, 2012
Senior subordinated convertible notes, interest percentage 3.75% 3.75%