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Earnings per Share - Common Stock Equivalents Not Included in Computation of Diluted Earnings Per Share (Detail) (USD $)
3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Mar. 31, 2013
Stock Options [Member]
Mar. 31, 2012
Stock Options [Member]
Mar. 31, 2013
Restricted Stock [Member]
Mar. 31, 2012
Restricted Stock [Member]
Mar. 31, 2013
Minimum [Member]
Stock Options [Member]
Mar. 31, 2012
Minimum [Member]
Stock Options [Member]
Mar. 31, 2013
Minimum [Member]
Restricted Stock [Member]
Mar. 31, 2012
Minimum [Member]
Restricted Stock [Member]
Mar. 31, 2013
Maximum [Member]
Stock Options [Member]
Mar. 31, 2012
Maximum [Member]
Stock Options [Member]
Mar. 31, 2013
Maximum [Member]
Restricted Stock [Member]
Mar. 31, 2012
Maximum [Member]
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                            
Antidilutive securities excluded from computation of earnings per share (in shares)     82,041 380,677 0 68,995                
Common stock, par value (in dollars per share) $ 1 $ 1         $ 9.19 $ 6.36 $ 0 $ 5.96 $ 14.55 $ 14.55 $ 0 $ 6.82