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, 2013
Dec. 31, 2012
Feb. 13, 2013
Jun. 03, 2010
Jun. 13, 2011
Common stock
Dec. 31, 2013
Common stock
Dec. 31, 2012
Common stock
Dec. 31, 2012
Common stock
Maximum
Class of Stock [Line Items]                  
Shares of common stock issued in private placements             1,476,789 212,500  
Private placements, price in usd per share             $ 4.50   $ 3.2
Stock issuance costs             $ 678,746    
Net cash proceeds from private placements             5,966,805 680,000  
Redeemable common stock           500,000      
Redeemable common stock, redemption right maximum period           5 years      
Common stock, shares outstanding   15,156,600 13,611,974            
Preferred stock, shares authorized       10,000,000          
Promissory note to investor         345,000        
Promissory note to investor, interest rate margin on Bank Prime Rate         3.00%        
Promissory note to investor, shares held as collateral         287,500        
Promissory note to investor, repaid with cash $ 105,000 $ 0 $ 105,000            
Promissiory note to investor, repaid with return of shares 100,000                
Promissiory note to investor, repaid with return of shares, price in usd per share $ 2.40