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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
Oct. 31, 2012
Apr. 30, 2012
Schedule of Available-for-sale Securities [Line Items]    
Fair Value    $ 840
Unrealized Losses    (175)
Fair Value 129   
Unrealized Losses (1)   
Fair Value 129 840
Unrealized Losses (1) (175)
Fixed income securities
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value    301
Unrealized Losses    (6)
Fair Value      
Unrealized Losses      
Fair Value    301
Unrealized Losses    (6)
Equity securities
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value    539
Unrealized Losses    (169)
Fair Value 129   
Unrealized Losses (1)   
Fair Value 129 539
Unrealized Losses $ (1) $ (169)