Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Common Stock and Receivable from Shareholder (Details)

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Stockholders' equity - Common Stock and Receivable from Shareholder (Details) (USD $)
 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 07, 2012
Dec. 31, 2012
Dec. 31, 2011
Jun. 03, 2010
Jun. 13, 2011
Common stock
Dec. 31, 2012
Common stock
Dec. 31, 2011
Common stock
Dec. 31, 2011
Common stock
Minimum
Dec. 31, 2011
Common stock
Maximum
Class of Stock [Line Items]                  
Shares of common stock issued in private placements           850,000 4,716,919    
Private placements, price in usd per share           $ 0.8   $ 0.65 $ 0.80
Net cash proceeds from private placements           $ 680,000 $ 3,610,993    
Redeemable common stock   0 0   500,000        
Redeemable common stock, redemption right maximum period         5 years        
Common stock, shares outstanding   54,447,854 53,993,882            
Promissory note to investor   0 345,000 345,000          
Promissory note to investor, interest rate margin on Bank Prime Rate       3.00%          
Promissory note to investor, shares held as collateral       1,150,000          
Promissory note to investor, repaid with cash $ 105,000 $ 105,000 $ 0            
Promissiory note to investor, repaid with return of shares 400,000                
Promissiory note to investor, repaid with return of shares, price in usd per share $ 0.60