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
 6 Months Ended
Jun. 30, 2012
security
Dec. 31, 2011
Jun. 30, 2011
Dec. 31, 2010
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 202,639 $ 247,640    
Cash and cash equivalents 26,151 18,633 42,952 8,877
Available-for-sale securities 176,488 229,007    
Cash equivalents and available-for-sale securities        
Amortized Cost 185,400 235,001    
Gross Unrealized Gains 96 76    
Gross Unrealized Losses (59) (70)    
Fair Value 185,437 235,007    
Years to Maturity        
Within One Year 154,898      
After One Year Through Five Years 46,432      
Weighted-average time to maturity of cash equivalents and available-for-sale securities 266 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 31      
Fair Value 78,169      
Unrealized Losses (59)      
Money market funds
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 15,893 11,947    
Years to Maturity        
Within One Year 15,893      
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 80,085 144,599    
Cash equivalents and available-for-sale securities        
Amortized Cost 80,080 144,602    
Gross Unrealized Gains 18 27    
Gross Unrealized Losses (13) (30)    
Fair Value 80,085 144,599    
Years to Maturity        
Within One Year 44,295      
After One Year Through Five Years 35,790      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 37,028      
Unrealized Losses (13)      
Corporate bonds and commercial paper
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 105,352 87,406    
Cash equivalents and available-for-sale securities        
Amortized Cost 105,320 87,398    
Gross Unrealized Gains 78 48    
Gross Unrealized Losses (46) (40)    
Fair Value 105,352 87,406    
Years to Maturity        
Within One Year 94,710      
After One Year Through Five Years 10,642      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 41,141      
Unrealized Losses (46)      
Checking account
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 1,309 $ 686