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Dividends - Additional Information (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dividends [Line Items]    
Declared and paid dividends $ 4.9 $ 4.8
Declared and paid dividends, per share $ 0.05 $ 0.05