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Fair Value and Unrealized Losses, Aggregated by Investment Type and Length of Time Individual Securities have been in Continuous Unrealized Loss Position (Detail) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2012
Apr. 30, 2012
Schedule of Available-for-sale Securities [Line Items]    
Fair Value $ 466 $ 840
Unrealized Losses (86) (175)
Fair Value 128  
Unrealized Losses (2)  
Fair Value 594 840
Unrealized Losses (88) (175)
Fixed Income Securities
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value 100 301
Unrealized Losses (2) (6)
Fair Value 100 301
Unrealized Losses (2) (6)
Equity Securities
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value 366 539
Unrealized Losses (84) (169)
Fair Value 128  
Unrealized Losses (2)  
Fair Value 494 539
Unrealized Losses $ (86) $ (169)