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Stockholders' Equity - Summary of Warrant Activity (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Warrants outstanding [Roll Forward]        
Outstanding, beginning of period (in shares) 78 44 9  
Issued (in shares) 14,256 30 35  
Exercised (in shares) (246) (3)    
Expired (in shares) (39) (3)    
Outstanding, end of period (in shares) 14,049 78 44 9
Warrants, Weighted Average Exercise Price [Roll Forward]        
Outstanding, beginning of period (in dollars per share) $ 910,000 $ 44,858,633 $ 15,170,879  
Issued (in dollars per share) 2,299 840,000 2,240,000  
Exercised (in dollars per share) 4,221 481,250 2,296,000  
Expired (in dollars per share) 845,250 994,000 2,296,000  
Outstanding, end of period (in dollars per share) $ 1,569 $ 910,000 $ 44,858,633 $ 15,170,879
Weighted average remaining life 4 years 10 months 17 days 5 years 7 months 2 days 2 years 1 month 28 days 2 years 9 months 11 days
Minimum [Member]        
Warrants, Exercise Price per Share [Roll Forward]        
Outstanding, (in dollars per share) $ 1,225 $ 281,750 $ 2,072,000 $ 4,900,000
Maximum [Member]        
Warrants, Exercise Price per Share [Roll Forward]        
Outstanding, (in dollars per share) $ 19,712,000 $ 19,712,000 $ 19,712,000 $ 19,712,000