Annual report pursuant to Section 13 and 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
 12 Months Ended
Dec. 31, 2012
item
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 298,241 $ 247,640    
Cash and cash equivalents 33,484 18,633 8,877 14,717
Available-for-sale securities 264,757 229,007    
Cash equivalents and available-for-sale securities        
Amortized Cost 273,972 235,001    
Gross Unrealized Gains 135 76    
Gross Unrealized Losses (53) (70)    
Fair Value 274,054 235,007    
Years to Maturity        
Within One Year 243,604      
After One Year Through Two Years 54,386      
Weighted-average time to maturity of cash equivalents and available-for-sale securities 212 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 25      
Fair Value 78,511      
Unrealized Losses (53)      
Money market funds
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 23,936 11,947    
Years to Maturity        
Within One Year 23,936      
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 77,047 144,599    
Cash equivalents and available-for-sale securities        
Amortized Cost 77,041 144,602    
Gross Unrealized Gains 37 27    
Gross Unrealized Losses (31) (30)    
Fair Value 77,047 144,599    
Years to Maturity        
Within One Year 53,973      
After One Year Through Two Years 23,074      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 6,288      
Unrealized Losses (31)      
Corporate bonds and commercial paper
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities 197,007 87,406    
Cash equivalents and available-for-sale securities        
Amortized Cost 196,931 87,398    
Gross Unrealized Gains 98 48    
Gross Unrealized Losses (22) (40)    
Fair Value 197,007 87,406    
Years to Maturity        
Within One Year 165,695      
After One Year Through Two Years 31,312      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 72,223      
Unrealized Losses (22)      
Checking account
        
Cash, cash equivalents and available-for-sale securities        
Cash, cash equivalents and available-for-sale securities $ 251 $ 686