Quarterly report pursuant to Section 13 or 15(d)

Fair Value (Details)

v2.4.0.6
Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis $ 32,816 $ 41,937
Level 1 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 18,861 25,399
Level 2 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 13,955 16,538
Level 3 [Member]
   
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 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 17,931 24,789
Money market funds [Member] | Level 1 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 17,931 24,789
Money market funds [Member] | Level 2 [Member]
   
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 [Member] | Level 3 [Member]
   
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 [Member]
   
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
Commercial paper [Member] | Level 1 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis   0
Commercial paper [Member] | Level 2 [Member]
   
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
Commercial paper [Member] | Level 3 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis   0
Corporate bonds [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 8,446 9,522
Corporate bonds [Member] | Level 1 [Member]
   
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 [Member] | Level 2 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 8,446 9,522
Corporate bonds [Member] | Level 3 [Member]
   
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 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 5,509 5,516
U.S. Treasury obligations [Member] | Level 1 [Member]
   
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 [Member] | Level 2 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 5,509 5,516
U.S. Treasury obligations [Member] | Level 3 [Member]
   
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 Solution [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 930 610
Common shares of CO2 Solution [Member] | Level 1 [Member]
   
Summary of financial instruments measured at fair value on a recurring basis    
Total financial assets measured at fair value on a recurring basis 930 610
Common shares of CO2 Solution [Member] | Level 2 [Member]
   
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 Solution [Member] | Level 3 [Member]
   
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