Quarterly report pursuant to Section 13 or 15(d)

Stockholders' equity (Details)

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Stockholders' equity (Details) (USD $)
 1 Months Ended 9 Months Ended
May 31, 2013
Sep. 30, 2013
Dec. 31, 2012
Stockholders' equity [Abstract]      
Common stock, shares authorized   60,000,000 60,000,000
Common stock, shares authorized before increase   30,000,000  
Stock issued during period, shares 11,500,000 6,100,000  
Common stock, price per share $ 1.25 $ 2.00  
Stock issued during period $ 14,400,000 $ 12,200,000  
Costs associated with the public offering $ 1,405,000 $ 1,261,000  
Placement fee percentage 7.00% 7.00%  
Warrants, number of shares per warrant 0.35    
Warrants, number of shares 4,025,000 305,000  
Warrants, exercise price 1.36 2.50  
Underwriter, addtional shares purchased 15.00%