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Marketable Securities (Summary Of Marketable Securities) (Details) (USD $)
Oct. 31, 2011
Apr. 30, 2011
Total, Trading $ 78,432,000 $ 71,363,000
Less: current portion of marketable securities, Trading (6,095,000) (5,081,000)
Non-current marketable securities, Trading 72,337,000 66,282,000
Total, Available-for-Sale 47,509,000 [1] 50,868,000 [1]
Less: current portion of marketable securities, Available-for-Sale (19,809,000) [1] (15,787,000) [1]
Non-current marketable securities, Available-for-Sale 27,700,000 [1] 35,081,000 [1]
Total 125,941,000 122,231,000
Less: current portion of marketable securities (25,904,000) (20,868,000)
Non-current marketable securities 100,037,000 101,363,000
Mutual Funds [Member]
    
Total, Trading 78,432,000 [2] 71,363,000 [2]
Total 78,432,000 [2] 71,363,000 [2]
Investments held in trust under deferred compensation plans 6,100,000 5,100,000
Corporate Bonds [Member]
    
Total, Available-for-Sale 45,090,000 [1] 40,444,000 [1]
Total 45,090,000 40,444,000
U.S. Treasury And Agency Securities [Member]
    
Total, Available-for-Sale 2,419,000 [1] 9,424,000 [1]
Total 2,419,000 9,424,000
Commercial Paper [Member]
    
Total, Available-for-Sale   1,000,000 [1]
Total   $ 1,000,000
[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 $6.1 million and $5.1 million classified as current assets as of October 31, 2011 and April 30, 2011, respectively (see Note 7).