Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities (Continuous Unrealized Loss Position) (Details)

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Marketable Securities (Continuous Unrealized Loss Position) (Details) (USD $)
 3 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Investments in an Unrealized Loss Position    
Months in Loss Position Not Exceeding this Period 12  
Fair Value $ 444,425,000  
Gross Unrealized Losses (2,577,000)  
Net realized securities gains 700,000 1,000,000
US Treasury securities
    
Investments in an Unrealized Loss Position    
Fair Value 25,868,000  
Gross Unrealized Losses (36,000) [1]  
US Government agency securities
    
Investments in an Unrealized Loss Position    
Fair Value 134,278,000  
Gross Unrealized Losses (338,000) [1]  
Municipal securities
    
Investments in an Unrealized Loss Position    
Fair Value 1,443,000  
Gross Unrealized Losses (3,000) [1]  
Corporate debt securities
    
Investments in an Unrealized Loss Position    
Fair Value 280,339,000  
Gross Unrealized Losses (2,196,000) [1]  
Sovereign securities
    
Investments in an Unrealized Loss Position    
Fair Value 2,497,000  
Gross Unrealized Losses $ (4,000) [1]  
[1] As of September 30, 2011, the amount of total gross unrealized losses that had been in a continuous loss position for 12 months or more was immaterial.