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Marketable Securities (Summary Of Assets Measured At Fair Value On Recurring Basis) (Details) (USD $)
In Thousands
Jul. 31, 2011
Apr. 30, 2011
Total, Trading $ 79,177 $ 71,363
Less: current portion of marketable securities, Trading (5,689) (5,081)
Non-current marketable securities, Trading 73,488 66,282
Total, Available-for-Sale 45,098 [1] 50,868 [1]
Less: current portion of marketable securities, Available-for-Sale (15,543) [1] (15,787) [1]
Non-current marketable securities, Available-for-Sale 29,555 [1] 35,081 [1]
Total 124,275 122,231
Less: current portion of marketable securities (21,232) (20,868)
Non-current marketable securities 103,043 101,363
Trading securities, current 5,689 5,081
Mutual Funds [Member]
    
Total, Trading 79,177 [2] 71,363 [2]
Total 79,177 [2] 71,363 [2]
Corporate Bonds [Member]
    
Total, Available-for-Sale 42,681 [1] 40,444 [1]
Total 42,681 40,444
U.S. Treasury And Agency Securities [Member]
    
Total, Available-for-Sale 2,417 [1] 9,424 [1]
Total 2,417 9,424
Commercial Paper [Member]
    
Total, Available-for-Sale   1,000 [1]
Total   $ 1,000
[1] These securities represent excess cash invested, under our investment policy, with a professional money manager.
[2] These investments are held in trust for settlement of the Company's obligations under certain of its deferred compensation plans with $5.7 million and $5.1 million classified as current assets as of July 31, 2011 and April 30, 2011, respectively (see Note 7).