Quarterly report pursuant to Section 13 or 15(d)

Stock options and warrants (Schedule of Nonvested Awards) (Details)

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Stock options and warrants (Schedule of Nonvested Awards) (Details) - Stock Incentive Plan [Member] - $ / shares
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Nonvested Shares Underlying Options    
Beginning balance 319,652  
Granted 1,094,500  
Vested (287,670)  
Forfeited (164,915) (4,565)
Ending balance 961,567  
Weighted Average Exercise Price    
Beginning balance $ 2.28  
Granted 1.89  
Vested 2.03  
Forfeited 2.06 $ 2.12
Ending balance 1.95  
Weighted Average Grant Date Fair Value    
Beginning balance 1.85  
Granted 1.34  
Vested 1.56  
Forfeited 1.48  
Ending balance $ 1.42