Quarterly report pursuant to Section 13 or 15(d)

Offerings of Common Stock and Warrants and At-the-Market Offering Program (Details)

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Offerings of Common Stock and Warrants and At-the-Market Offering Program (Details) - USD ($)
 3 Months Ended 46 Months Ended
Apr. 13, 2018
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Mar. 31, 2019
Feb. 04, 2019
Jun. 07, 2018
Aug. 28, 2015
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Common stock sold (in shares) 3,806,243              
Common stock, par value (in dollars per share)   $ 0.001   $ 0.001 $ 0.001      
Aggregate offering price of common stock   $ 1,222,000 $ 4,970,000          
June 2018 Sales Agreement                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Aggregate offering price for at-the-market offering program   $ 16,500,000   $ 16,500,000        
Common stock sold (in shares)   1,400,000            
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars)   $ 1,200,000            
Common stock commissions paid   $ 44,300            
June 2018 Sales Agreement | Maximum                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Aggregate offering price for at-the-market offering program             $ 25,000,000  
August 2015 Sales Agreement                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Common stock sold (in shares)     2,800,000 26,000,000        
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars)     $ 4,000,000 $ 28,600,000        
Common stock commissions paid     $ 100,000 $ 800,000        
August 2015 Sales Agreement | Maximum                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Aggregate offering price for at-the-market offering program               $ 30,000,000
Goldman Sachs & Co. LLC                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Exercise price (in dollars per share)           $ 0.8859    
Common stock, par value (in dollars per share)           $ 0.001    
Value of the Warrant           $ 2,300,000    
Goldman Sachs & Co. LLC | Maximum                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Outstanding warrants (in shares)           4,046,337    
Goldman Sachs & Co. LLC | Private Placement                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Value of the Warrant           $ 150,000    
Series A Warrants                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Warrants exercised (in shares) 5,760,000              
Exercise price (in dollars per share) $ 0.60              
Outstanding warrants (in shares)   2,718,750   2,718,750        
Series A Warrants, Exercise Price 2.55                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Exercise price (in dollars per share)   $ 2.55   $ 2.55        
Issued warrants (in shares)   2,178,750            
Series A Warrants, Exercise Price 1.34                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Exercise price (in dollars per share)   $ 0.57   0.57        
Initial exercise price (in dollars per share)   $ 1.34   $ 1.34        
Issued warrants (in shares)   540,000            
Series B Warrants                
Offerings of Common Stock and Warrants and At-the-Market Offering Program                
Outstanding warrants (in shares)   0   0