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
 3 Months Ended
Mar. 31, 2013
item
Dec. 31, 2012
Mar. 31, 2012
Dec. 31, 2011
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 272,450 $ 298,241    
Cash and cash equivalents 34,159 33,484 22,033 18,633
Available-for-sale securities 238,291 264,757    
Cash equivalents and available-for-sale securities        
Amortized Cost 263,162 273,972    
Gross Unrealized Gains 114 135    
Gross Unrealized Losses (36) (53)    
Fair Value 263,240 274,054    
Years to Maturity        
Within One Year 208,879      
After One Year Through Two Years 54,361      
Weighted-average time to maturity of cash equivalents and available-for-sale securities 214 days      
Stated maturity period may be greater than this period and classified as current 1 year      
Investments in unrealized loss position for more than twelve months 0 0    
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 24      
Money market funds
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 9,053 23,936    
Government-sponsored enterprise securities
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 75,233 77,047    
Cash equivalents and available-for-sale securities        
Amortized Cost 75,196 77,041    
Gross Unrealized Gains 37 37    
Gross Unrealized Losses   (31)    
Fair Value 75,233 77,047    
Years to Maturity        
Within One Year 44,121      
After One Year Through Two Years 31,112      
Corporate bonds and commercial paper
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 188,007 197,007    
Cash equivalents and available-for-sale securities        
Amortized Cost 187,966 196,931    
Gross Unrealized Gains 77 98    
Gross Unrealized Losses (36) (22)    
Fair Value 188,007 197,007    
Years to Maturity        
Within One Year 164,758      
After One Year Through Two Years 23,249      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 56,609      
Unrealized Losses (36)      
Checking account
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 157 $ 251