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Cash, Cash Equivalents and Marketable Securities (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Jun. 30, 2011
Dec. 31, 2010
Cash, cash equivalents and marketable securities          
Cash And Cash Equivalents Short Term Investment Amortized Cost $ 93,816   $ 97,727    
Cash And Cash Equivalents Short Term Investment Unrealized Gains 44   128    
Cash and Cash Equivalents Short Term Investment Unrealized Loss (1)         
Cash and Cash Equivalents Short Term Investment Fair Value 93,942 93,942 98,131    
Cash and cash equivalents 79,020   73,144 [1] 62,830 4,798
Marketable Securities 14,922   24,987 [1]    
Accrued Interest 83   276    
Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Cash and Cash Equivalents Short Term Investment Fair Value 93,859   97,855    
Marketable Securities [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities Amortized Cost 14,799   24,583    
Marketable Securities Unrealized Gains 41   128    
Marketable Securities Unrealized Losses (1)         
Marketable Securities 14,922   24,987    
Accrued Interest 83   276    
Marketable Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities     24,711 14,839  
Cash and Cash Equivalents [Member]
          
Cash, cash equivalents and marketable securities          
Cash and Cash Equivalents Amortized Cost 28,886   73,144    
Cash And Cash Equivalents Unrealized Gains            
Cash and Cash Equivalents Unrealized Losses            
Cash and cash equivalents 28,886   73,144    
Accrued Interest            
Cash and Cash Equivalents [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Cash and cash equivalents 28,886   73,144    
Commercial Paper [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities Amortized Cost 54,928        
Marketable Securities Unrealized Gains 5        
Marketable Securities Unrealized Losses (1)        
Marketable Securities 54,932        
Accrued Interest           
Commercial Paper [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities 54,932        
Corporate securities [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities Amortized Cost 10,002   24,583    
Marketable Securities Unrealized Gains 39   128    
Marketable Securities Unrealized Losses            
Marketable Securities 10,124   24,987    
Accrued Interest 83   276    
Corporate securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Marketable Securities 10,041   24,711    
Cash and Cash Equivalents Reported Value [Member]
          
Cash, cash equivalents and marketable securities          
Cash and Cash Equivalents Amortized Cost 79,017   73,144    
Cash And Cash Equivalents Unrealized Gains 3         
Cash and Cash Equivalents Unrealized Losses            
Cash and cash equivalents 79,020   73,144    
Accrued Interest            
Cash and Cash Equivalents Reported Value [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Cash and cash equivalents 79,020   73,144    
Matured in One Year or Less [Member]
          
Cash, cash equivalents and marketable securities          
Cash And Cash Equivalents Short Term Investment Amortized Cost 93,816   97,727    
Cash And Cash Equivalents Short Term Investment Unrealized Gains 44   128    
Cash and Cash Equivalents Short Term Investment Unrealized Loss (1)         
Cash and Cash Equivalents Short Term Investment Fair Value 93,942   98,131    
Accrued Interest 83   276    
Matured in One Year or Less [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Cash and Cash Equivalents Short Term Investment Fair Value 93,859   97,855    
Matured in One to Three Years [Member]
          
Cash, cash equivalents and marketable securities          
Cash And Cash Equivalents Short Term Investment Amortized Cost            
Cash And Cash Equivalents Short Term Investment Unrealized Gains            
Cash and Cash Equivalents Short Term Investment Unrealized Loss            
Cash and Cash Equivalents Short Term Investment Fair Value            
Accrued Interest            
Matured in One to Three Years [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
          
Cash, cash equivalents and marketable securities          
Cash and Cash Equivalents Short Term Investment Fair Value            
[1] (1) Derived from the Company's audited financial statements as of December 31, 2011, included in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission.