Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details)

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Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Oct. 31, 2015
Oct. 31, 2014
Stock-based compensation    
Expected volatility, minimum (as a percent) 88.96% 88.82%
Expected volatility, maximum (as a percent) 89.70% 92.83%
Risk-free interest rate, minimum (as a percent) 0.86% 0.36%
Risk-free interest rate, maximum (as a percent) 1.74% 2.13%
Expected forfeiture rate (as a percent) 0.00% 0.00%
Stock-based compensation expense recognized $ 1.5 $ 0.6
Weighted-average grant date fair value (in dollars per share) $ 4.15 $ 7.20
Minimum    
Stock-based compensation    
Expected term 2 years 9 months 18 days 2 years
Maximum    
Stock-based compensation    
Expected term 6 years 6 months 7 years
Research and development expense.    
Stock-based compensation    
Stock-based compensation expense recognized $ 0.3 $ 0.3
General and administrative expenses.    
Stock-based compensation    
Stock-based compensation expense recognized $ 1.2 $ 0.3
2011 Plan | Employees    
Stock-based compensation    
Term of stock options   10 years
Options granted to purchase shares   107,500
Exercise price, low end of the range (in dollars per share)   $ 8.80
Exercise price, high end of the range (in dollars per share)   $ 10.40
2011 Plan | Employees | Minimum    
Stock-based compensation    
Vesting period   2 years
2011 Plan | Employees | Maximum    
Stock-based compensation    
Vesting period   3 years
2011 Plan | Consultants    
Stock-based compensation    
Options granted to purchase shares 61,000 25,000
Exercise price, low end of the range (in dollars per share)   $ 7.80
Exercise price, high end of the range (in dollars per share)   $ 8.60
Exercise price (in dollars per share) $ 5.76  
2011 Plan | Consultants | Minimum    
Stock-based compensation    
Term of stock options   1 year
2011 Plan | Consultants | Maximum    
Stock-based compensation    
Term of stock options 3 years 3 years
2011 Plan | Employees and directors    
Stock-based compensation    
Term of stock options 10 years  
Options granted to purchase shares 1,982,500  
Exercise price, low end of the range (in dollars per share) $ 4.15  
Exercise price, high end of the range (in dollars per share) $ 6.21  
2011 Plan | Employees and directors | Minimum    
Stock-based compensation    
Vesting period 1 year  
2011 Plan | Employees and directors | Maximum    
Stock-based compensation    
Vesting period 3 years