Quarterly report pursuant to Section 13 or 15(d)

Cash, Cash Equivalents and Available-For-Sale Securities (Details)

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Cash, Cash Equivalents and Available-For-Sale Securities (Details) (USD $)
In Thousands, unless otherwise specified
 9 Months Ended
Sep. 30, 2012
item
Dec. 31, 2011
Sep. 30, 2011
Dec. 31, 2010
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 183,895 $ 247,640    
Cash and cash equivalents 26,801 18,633 18,682 8,877
Available-for-sale securities 157,094 229,007    
Cash equivalents and available-for-sale securities        
Amortized Cost 174,475 235,001    
Gross Unrealized Gains 121 76    
Gross Unrealized Losses (15) (70)    
Fair Value 174,581 235,007    
Years to Maturity        
Within One Year 149,010      
After One Year Through Five Years 34,769      
Weighted-average time to maturity of cash equivalents and available-for-sale securities 207 days      
Stated maturity period may be greater than this period and classified as current 1 year      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Number of individual securities in unrealized loss position for twelve months or less 8      
Money market funds
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 9,198 11,947    
Years to Maturity        
Within One Year 9,198      
U. S. treasury bills
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities   3,002    
Cash equivalents and available-for-sale securities        
Amortized Cost   3,001    
Gross Unrealized Gains   1    
Fair Value   3,002    
Government-sponsored enterprise securities
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 50,902 144,599    
Cash equivalents and available-for-sale securities        
Amortized Cost 50,867 144,602    
Gross Unrealized Gains 35 27    
Gross Unrealized Losses   (30)    
Fair Value 50,902 144,599    
Years to Maturity        
Within One Year 27,196      
After One Year Through Five Years 23,706      
Corporate bonds and commercial paper
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 123,679 87,406    
Cash equivalents and available-for-sale securities        
Amortized Cost 123,608 87,398    
Gross Unrealized Gains 86 48    
Gross Unrealized Losses (15) (40)    
Fair Value 123,679 87,406    
Years to Maturity        
Within One Year 112,616      
After One Year Through Five Years 11,063      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 18,164      
Unrealized Losses (15)      
Checking account
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 116 $ 686