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, 2014
item
Dec. 31, 2013
Mar. 31, 2013
Dec. 31, 2012
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 195,384 $ 211,975    
Cash and cash equivalents 14,910 20,854 34,159 33,484
Available-for-sale securities 180,474 191,121    
Cash equivalents and available-for-sale securities        
Amortized Cost 181,312 202,674    
Gross Unrealized Gains 64 64    
Gross Unrealized Losses (26) (17)    
Fair Value 181,350 202,721    
Years to Maturity        
Within One Year 152,726      
After One Year Through Two Years 28,624      
Weighted-average time to maturity of cash equivalents and available-for-sale securities 197 days      
Stated maturity period may be greater than this period and classified as current 1 year      
Number of investments in continuous unrealized loss position for more than twelve months 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 31      
Other-than-temporary impairments of securities 0      
Fair Value 64,463      
Unrealized Losses (26)      
Money market funds
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 13,625 9,059    
U. S. treasury bills
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 2,068 2,085    
Cash equivalents and available-for-sale securities        
Amortized Cost 2,065 2,083    
Gross Unrealized Gains 3 2    
Fair Value 2,068 2,085    
Years to Maturity        
Within One Year 2,068      
Government-sponsored enterprise securities
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 62,827 67,178    
Cash equivalents and available-for-sale securities        
Amortized Cost 62,799 67,160    
Gross Unrealized Gains 34 29    
Gross Unrealized Losses (6) (11)    
Fair Value 62,827 67,178    
Years to Maturity        
Within One Year 45,326      
After One Year Through Two Years 17,501      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 15,697      
Unrealized Losses (6)      
Corporate bonds and commercial paper
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 116,455 133,458    
Cash equivalents and available-for-sale securities        
Amortized Cost 116,448 133,431    
Gross Unrealized Gains 27 33    
Gross Unrealized Losses (20) (6)    
Fair Value 116,455 133,458    
Years to Maturity        
Within One Year 105,332      
After One Year Through Two Years 11,123      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 48,766      
Unrealized Losses (20)      
Checking account
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 409 $ 195