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Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Mar. 31, 2012
Dec. 31, 2011
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and cash equivalents $ 51,591 $ 49,355 [1] $ 73,779 $ 73,144
Cash And Cash Equivalents Short Term Investment Amortized Cost 54,390 56,250    
Cash And Cash Equivalents Short Term Investment Unrealized Gains 1 4    
Cash and Cash Equivalents Short Term Investment Unrealized Loss          
Estimated Fair Value, Marketable securities 2,800 6,899 [1]    
Cash and Cash Equivalents Short Term Investment Fair Value 54,391 56,254    
Accrued Interest          
Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and Cash Equivalents Short Term Investment Fair Value 54,391 56,254    
Marketable Securities [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Available-for-sale Securities, Amortized Cost Basis 25,676 6,898    
Available-for-sale Securities, Gross Unrealized Gains 1 1    
Available-for-sale Securities, Gross Unrealized Losses          
Estimated Fair Value, Marketable securities 25,677 6,899    
Accrued Interest          
Marketable Securities [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Estimated Fair Value, Marketable securities 25,677 6,899    
Cash and Cash Equivalents [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and cash equivalents 28,714 49,352    
Available-for-sale Securities, Gross Unrealized Gains    3    
Available-for-sale Securities, Gross Unrealized Losses          
Accrued Interest          
Cash and Cash Equivalents [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and cash equivalents 28,714 49,355    
Corporate Securities [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Available-for-sale Securities, Amortized Cost Basis 25,676 6,898    
Available-for-sale Securities, Gross Unrealized Gains 1 1    
Available-for-sale Securities, Gross Unrealized Losses          
Estimated Fair Value, Marketable securities 25,677 6,899    
Accrued Interest          
Corporate Securities [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Estimated Fair Value, Marketable securities 25,677 6,899    
Cash and Cash Equivalents Reported Value [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and cash equivalents 28,714 49,352    
Available-for-sale Securities, Gross Unrealized Gains    3    
Available-for-sale Securities, Gross Unrealized Losses          
Accrued Interest          
Cash and Cash Equivalents Reported Value [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and cash equivalents 28,714 49,355    
Matured in One Year or Less [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash And Cash Equivalents Short Term Investment Amortized Cost 54,390 56,250    
Available-for-sale Securities, Gross Unrealized Gains 1 4    
Available-for-sale Securities, Gross Unrealized Losses          
Cash and Cash Equivalents Short Term Investment Fair Value 54,391 56,254    
Accrued Interest          
Matured in One Year or Less [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and Cash Equivalents Short Term Investment Fair Value 54,391 56,254    
Matured in One to Three Years [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash And Cash Equivalents Short Term Investment Amortized Cost          
Available-for-sale Securities, Gross Unrealized Gains          
Available-for-sale Securities, Gross Unrealized Losses          
Cash and Cash Equivalents Short Term Investment Fair Value          
Accrued Interest          
Matured in One to Three Years [Member] | Estimated Fair Value, Fair Value Disclosure [Member]
        
Cash, Cash Equivalents and Marketable Securities and Assets Measured at Fair Value        
Cash and Cash Equivalents Short Term Investment Fair Value          
[1] Derived from the Company's audited financial statements as of December 31, 2012, included in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission.