Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Equity Incentive Plans (Details)

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Stockholders' Equity - Equity Incentive Plans (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Options outstanding    
Equity Incentive Plans    
Stock-based compensation $ 3,426,730 $ 2,383,399
Options outstanding | Research and development    
Equity Incentive Plans    
Stock-based compensation 1,460,061 1,129,244
Options outstanding | General and administrative    
Equity Incentive Plans    
Stock-based compensation $ 1,966,669 $ 1,254,155
2008 and 2013 Plans | Maximum    
Equity Incentive Plans    
Term of award 10 years  
Vesting period 4 years