XML 30 R87.htm IDEA: XBRL DOCUMENT v2.4.0.6
Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Apr. 30, 2013
Apr. 30, 2012
Assets:    
Restricted assets $ 545 $ 424
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets 545 424
Liabilities:    
Interest rate derivatives      
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets      
Liabilities:    
Interest rate derivatives 4,229 2,369
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Restricted assets      
Liabilities:    
Interest rate derivatives