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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 5) (USD $)
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Fair Value Measurements        
Cash and cash equivalents $ 13,345,000 $ 35,781,000 $ 78,752,000 $ 21,924,000
Marketable securities        
Available-for-sale securities 94,776,000 57,580,000    
Available-for-sale securities in a countinuous unrealized loss position        
Total unrealized losses of available for sale securities in a continuous unrealized loss position for less than twelve months 4,800 285,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Due in one year or less 58,922,000      
Due after one year through two years 35,854,000      
Estimated Fair Value 94,776,000 57,580,000    
Contractual maturities of the available-for-sale investments, Cost        
Due in one year or less 58,882,000      
Due after one year through two years 35,816,000      
Cost 94,698,000      
Concentration of Credit Risk        
Cash and cash equivalents, federal government agency insured limit 250,000      
Cash and cash equivalents in excess of federal government agency insured limit 13,100,000      
Fair Value
       
Marketable securities        
Available-for-sale securities 103,181,000 92,965,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 103,181,000 92,965,000    
Fair Value | Cash equivalents
       
Marketable securities        
Available-for-sale securities 8,405,000 35,385,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 8,405,000 35,385,000    
Fair Value | U.S. government agency securities
       
Marketable securities        
Available-for-sale securities 44,308,000 27,994,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 44,308,000 27,994,000    
Fair Value | Certificates of deposit
       
Marketable securities        
Available-for-sale securities 5,939,000 9,465,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 5,939,000 9,465,000    
Fair Value | Corporate bonds
       
Marketable securities        
Available-for-sale securities 43,330,000 19,122,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 43,330,000 19,122,000    
Fair Value | Commercial paper
       
Marketable securities        
Available-for-sale securities 1,199,000 999,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 1,199,000 999,000    
Quoted Prices in Active Markets for Identical Assets (Level1)
       
Marketable securities        
Available-for-sale securities 8,405,000 35,385,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 8,405,000 35,385,000    
Quoted Prices in Active Markets for Identical Assets (Level1) | Cash equivalents
       
Marketable securities        
Available-for-sale securities 8,405,000 35,385,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 8,405,000 35,385,000    
Significant Other Observable Inputs (Level 2)
       
Marketable securities        
Available-for-sale securities 94,776,000 57,580,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 94,776,000 57,580,000    
Significant Other Observable Inputs (Level 2) | U.S. government agency securities
       
Marketable securities        
Available-for-sale securities 44,308,000 27,994,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 44,308,000 27,994,000    
Significant Other Observable Inputs (Level 2) | Certificates of deposit
       
Marketable securities        
Available-for-sale securities 5,939,000 9,465,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 5,939,000 9,465,000    
Significant Other Observable Inputs (Level 2) | Corporate bonds
       
Marketable securities        
Available-for-sale securities 43,330,000 19,122,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value 43,330,000 19,122,000    
Significant Other Observable Inputs (Level 2) | Commercial paper
       
Marketable securities        
Available-for-sale securities 1,199,000 999,000    
Contractual maturities of the available-for-sale investments, Fair Value        
Estimated Fair Value $ 1,199,000 $ 999,000