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Fair value of financial instruments and marketable securities (Details 4) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Jun. 30, 2013
Common stock
Mar. 31, 2014
Warrant
Mar. 31, 2014
Warrant
Minimum
Dec. 31, 2013
Warrant
Minimum
Mar. 31, 2014
Warrant
Maximum
Dec. 31, 2013
Warrant
Maximum
Mar. 31, 2014
Warrant
Common stock
Dec. 31, 2013
Warrant
Common stock
Changes in the fair value of warrant liability                
Beginning balance   $ 58            
Change in fair value of warrant liability   55            
Ending balance   $ 113            
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model                
Volatility (as a percent)     58.00% 61.00% 90.00% 89.00%    
Risk-free interest rate (as a percent)     0.03% 0.07% 1.73% 2.10%    
Strike price (in dollars per share)     $ 128.00 $ 128.00 $ 2,520.00 $ 2,520.00    
Fair value of shares (in dollars per share) $ 15.00           $ 26.14 $ 16.97
Expected life     22 days 3 months 18 days 5 years 5 months 23 days 5 years 8 months 12 days