Annual report pursuant to Section 13 and 15(d)

Fair Value (Financial Assets measured at Fair Value on a Recurring Basis) (Details)

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Fair Value (Financial Assets measured at Fair Value on a Recurring Basis) (Details) (USD $)
Dec. 31, 2012
Dec. 31, 2011
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis $ 41,937,000 $ 56,935,000
Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 25,399,000 20,027,000
Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 16,538,000 36,908,000
Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Money market funds
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 24,789,000 18,866,000
Money market funds | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 24,789,000 18,866,000
Money market funds | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Money market funds | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Commercial paper
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 1,500,000 1,999,000
Commercial paper | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Commercial paper | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 1,500,000 1,999,000
Commercial paper | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Corporate bonds
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 9,522,000 30,892,000
Corporate bonds | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Corporate bonds | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 9,522,000 30,892,000
Corporate bonds | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
U.S. Treasury obligations
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 5,516,000 1,002,000
U.S. Treasury obligations | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
U.S. Treasury obligations | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 5,516,000 1,002,000
U.S. Treasury obligations | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Government-sponsored enterprise securities
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 3,015,000
Government-sponsored enterprise securities | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Government-sponsored enterprise securities | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 3,015,000
Government-sponsored enterprise securities | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Common shares of CO2 Solutions
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 610,000 1,161,000
Common shares of CO2 Solutions | Level 1
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 610,000 1,161,000
Common shares of CO2 Solutions | Level 2
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 0 0
Common shares of CO2 Solutions | Level 3
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis $ 0 $ 0