Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities (Schedule Of Amortized Cost And Fair Values Of Available-For-Sale Investments) (Details)

v2.4.0.6
Marketable Securities (Schedule Of Amortized Cost And Fair Values Of Available-For-Sale Investments) (Details) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2012
Apr. 30, 2011
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 53,721 $ 50,796
Gross Unrealized Gains 85 117
Gross Unrealized Losses (98) [1] (45) [1]
Estimated Fair Value 53,708 50,868
Corporate Bonds [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 45,730 40,369
Gross Unrealized Gains 85 107
Gross Unrealized Losses (90) [1] (32) [1]
Estimated Fair Value 45,725 40,444
U.S. Treasury And Agency Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,003 9,427
Gross Unrealized Gains   10
Gross Unrealized Losses (1) [1] (13) [1]
Estimated Fair Value 2,002 9,424
Commercial Paper [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,988 1,000
Gross Unrealized Losses (7) [1]  
Estimated Fair Value $ 5,981 $ 1,000
[1] There are no marketable securities that have been in a continuous unrealized loss position for 12 months or more.