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Deferred Compensation And Retirement Plans (Components Of Net Periodic Benefit Costs) (Details) (USD $)
 3 Months Ended 6 Months Ended
Oct. 31, 2011
Oct. 31, 2010
Oct. 31, 2011
Oct. 31, 2010
Deferred Compensation And Retirement Plans [Abstract]        
Service cost   $ 34,000   $ 68,000
Interest cost 884,000 925,000 1,768,000 1,850,000
Amortization of actuarial loss 355,000 105,000 710,000 210,000
Net periodic benefit costs 1,239,000 1,064,000 2,478,000 2,128,000
Company contributions to the ECAP 3,000,000 100,000 15,300,000 400,000
Change in Fair Value of Vested Amounts owed under deferred compensation plan, (Income), Expense $ (2,300,000) $ 2,500,000 $ (3,600,000) $ 1,300,000
Deferred compensation arrangement vesting terms     Participants generally vest in Company contributions over a four year period.