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Stockholders' Equity - Preferred Stock and Common Stock - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended 28 Months Ended
Oct. 20, 2016
Jun. 18, 2015
Nov. 30, 2013
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2017
Apr. 24, 2017
Oct. 25, 2016
Aug. 31, 2015
Feb. 27, 2015
Aug. 31, 2013
Jul. 17, 2013
Jan. 31, 2012
May 31, 2008
Class Of Stock [Line Items]                              
Preferred stock, shares authorized       25,000,000     25,000,000                
Preferred stock, shares outstanding       0     0                
Issuance of common stock from stock options exercises, net, Shares       245,271 116,001 205,033                  
Issuance of common stock       104,551,466 92,391,989   104,551,466                
Common stock, par value       $ 0.001 $ 0.001   $ 0.001                
Issuance of common stock from warrant exercises, net, Shares       700,379 32,914 210,600                  
Warrants exercised       822,903 43,796 211,647                  
Stock option exercised       245,271 116,001 205,684                  
Equity Distribution Agreement [Member]                              
Class Of Stock [Line Items]                              
Value of shares sold under equity distribution agreement       $ 0 $ 0 $ 16,100,000                  
Issuance of common stock from stock options exercises, net, Shares       0 0 2,197,768                  
Equity Offering Sales Agreement [Member]                              
Class Of Stock [Line Items]                              
Value of shares sold under equity distribution agreement       $ 4,600,000 $ 0 $ 6,200,000 $ 10,800,000                
Issuance of common stock from stock options exercises, net, Shares       997,181 0 1,000,000                  
Issuance of common stock       1,997,181     1,997,181                
Additional common stocks under shelf registration       $ 21,900,000     $ 21,900,000                
2015 Underwriting Agreement [Member]                              
Class Of Stock [Line Items]                              
Stock option exercisable, period   30 days                          
Additional common stock issued on exercise of option by underwriters   1,413,750                          
Maximum [Member] | Equity Distribution Agreement [Member]                              
Class Of Stock [Line Items]                              
Number of shares to be offered and sold in equity distribution agreement     4,000,000                        
IPO [Member]                              
Class Of Stock [Line Items]                              
Securities authorized for offer and sale, amount                     $ 190,000,000   $ 100,000,000    
Secondary Offering | 2015 Underwriting Agreement [Member]                              
Class Of Stock [Line Items]                              
Issuance of common stock from stock options exercises, net, Shares   10,838,750                          
Common stock, par value   $ 0.001                          
Offering price per share   $ 4.25                          
Gross proceeds from sale of common stock shares   $ 43,100,000                          
Secondary Offering | 2016 Underwriting Agreement [Member]                              
Class Of Stock [Line Items]                              
Offering price per share $ 2.75                            
Gross proceeds from sale of common stock shares $ 25,700,000                            
Over Allotment Option [Member] | 2015 Underwriting Agreement [Member]                              
Class Of Stock [Line Items]                              
Issuance of common stock   9,425,000                          
Sale of stock price per share net of fees   $ 3.995                          
Over Allotment Option [Member] | 2016 Underwriting Agreement [Member]                              
Class Of Stock [Line Items]                              
Issuance of common stock                 10,065,000            
Sale of stock price per share net of fees $ 2.585                            
Equity Incentive Plan 2008 [Member]                              
Class Of Stock [Line Items]                              
Common shares authorized to be issued                             1,521,584
Termination date of equity incentive plan       Jul. 01, 2018                      
Shares issued during the year       0                      
Equity Incentive Plan 2012 [Member]                              
Class Of Stock [Line Items]                              
Common shares authorized to be issued                   6,000,000   5,000,000   6,553,986  
Shares available for issuance       3,617,386     3,617,386     17,553,986          
Termination period of Equity Incentive Plan       10 years                      
Inducement Award Agreements [Member] | Subsequent Event [Member]                              
Class Of Stock [Line Items]                              
Common shares authorized to be issued               2,297,034