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Fair Value Disclosure (Details) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2012
Apr. 30, 2011
Fair Value Disclosure [Abstract]    
Fair value of long-term debt excluding capital lease obligations $ 681,000 $ 636,000
Line of credit, maximum borrowing capacity 100,000  
Line of credit, amount owed $ 0 $ 600