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Fair Value Measurements - Summary of Changes in Fair Value of Company's Level 3 Financial Liabilities (Details) - Warrants - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Beginning balance $ 4,641 $ 280,303
Change in fair value of warrant liability   (275,662)
Change in fair value of warrant liability from repricing 244,611  
Change in fair value of warrant liability (208,480)  
Repurchase and retirement of warrants (40,772)  
Ending balance 0 4,641
2014 Offering    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Beginning balance 4,112 227,992
Change in fair value of warrant liability   (223,880)
Change in fair value of warrant liability from repricing 177,999  
Change in fair value of warrant liability (147,278)  
Repurchase and retirement of warrants (34,833)  
Ending balance 0 4,112
2013 Offering    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Beginning balance 529 52,311
Change in fair value of warrant liability   (51,782)
Change in fair value of warrant liability from repricing 66,612  
Change in fair value of warrant liability (61,202)  
Repurchase and retirement of warrants (5,939)  
Ending balance $ 0 $ 529