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Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Oct. 31, 2014
Apr. 30, 2014
Assets:    
Restricted assets $ 790 $ 681
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets 790 681
Liabilities:    
Interest rate derivatives 0 0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets 0 0
Liabilities:    
Interest rate derivatives 2,177 2,770
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets 0 0
Liabilities:    
Interest rate derivatives $ 0 $ 0