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Fair Value Disclosure (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2013
Apr. 30, 2012
Fair Value Disclosure [Abstract]    
Fair value of long-term debt excluding capital lease obligations $ 729,000 $ 691,000
Line of credit facility, maximum borrowing capacity 125,000  
Line of credit, amount owed $ 58,600  
Weighted average interest rate 0.95%