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Common Stock Dividends (Narrative) (Details) (USD $)
3 Months Ended 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Jan. 31, 2013
Jan. 31, 2012
Feb. 21, 2013
Dividends, Common Stock [Abstract]          
Percent increase in dividend over prior year 18.00%        
Common stock, quarterly dividends, per share, declared         $ 0.47
Annual dividend approved by Board of Directors $ 1.88 $ 1.59      
Common stock, dividends, per share, cash paid     $ 1.59 $ 1.46