Stockholders' Equity - Grants Outside of 2000 and 2017 Plans and Stockholder Rights Plan (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Oct. 27, 2017
USD ($)
$ / shares
Oct. 21, 2016
USD ($)
Oct. 18, 2016
$ / shares
shares
May 06, 2016
Vote
$ / shares
Apr. 22, 2016
USD ($)
Apr. 19, 2016
$ / shares
shares
Aug. 28, 2015
USD ($)
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2017
USD ($)
$ / shares
shares
Oct. 26, 2017
$ / shares
shares
Aug. 31, 2017
$ / shares
Stockholder Rights Plan                        
Preferred stock, par value (in dollars per share) | $ / shares               $ 0.001 $ 0.001 $ 0.001    
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars) | $         $ 13,100     $ 5,300 $ 11,900      
Common stock, par value (in dollars per share) | $ / shares $ 0.001             $ 0.001 $ 0.001 $ 0.001    
Reduction of warrants to purchase common stock (as a percent) 19.00%                      
Number of common stock shares available to accredited investors     3,600,000                  
Share price of common stock sold (in dollars per share) | $ / shares     $ 1.20                  
Loss on adjustment of exercise price | $                 $ 741 $ 421    
Net proceeds from offering of common stock and warrants | $   $ 6,800             $ 13,581 $ 20,188    
Number of common stock shares available in public offering           2,700,000            
Number of warrants or shares of common stock to be sold to purchase common stock           2            
Common stock sold (in shares)               6,700,000 16,000,000      
Common stock commissions paid | $               $ 200 $ 300      
Total shares of common stock sold pursuant to the at-the-market offering program               23,300,000 23,300,000      
Total net proceeds from sale of common stock | $               $ 24,600 $ 24,600      
Total common stock commissions paid | $               700 700      
Common stock available for issuance | $               $ 4,100 4,100      
Series A Warrants                        
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Number of shares of common stock that could be purchased with warrants           4,100,000         1,928,750  
Exercise price (in dollars per share) | $ / shares     1.34     $ 3.50         $ 0.90 $ 0.60
Net proceeds from sale of the common stock, after deducting fees and other offering expenses (in dollars) | $ $ 1,700                      
Loss on adjustment of exercise price | $                 $ 700      
Number of warrants or shares of common stock to be sold to purchase common stock           1            
Number of shares of common stock purchased with each warrant           1            
Length of time from issue date until warrants are exercisable           6 months            
Length of time from exercise date until warrants expire           5 years            
Outstanding warrants (in shares)               8,478,750 8,478,750      
Series B Warrants                        
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Number of shares of common stock that could be purchased with warrants           5,500,000            
Exercise price (in dollars per share) | $ / shares     1.20     $ 3.48            
Exercise price pre-funded at closing (in dollars per share) | $ / shares     1.19                  
Exercise price, payable upon exercise (in dollars per share) | $ / shares     $ 0.01                  
Number of warrants or shares of common stock to be sold to purchase common stock           2            
Number of shares of common stock purchased with each warrant           1            
Length of time from exercise date until warrants expire           9 months            
Outstanding warrants (in shares)               0 0      
Minimum | Series B Warrants                        
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Number of shares of common stock that could be purchased with warrants     2,700,000                  
Maximum                        
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Aggregate offering price for at-the-market offering program | $             $ 30,000          
Maximum | Series A Warrants                        
At-the-market Offering Program and Underwritten Offering of Common Stock                        
Number of shares of common stock that could be purchased with warrants     6,300,000                  
Stock options                        
Class of Stock [Line Items]                        
Options outstanding (in shares)               212,392 212,392 314,537    
Portion vesting one year after the issuance date (as a percent)                 25.00%      
Portion vesting on first day of each month after one year from the issuance date (as a percent)                 2.083%      
Expiration Term                 10 years      
Vesting period                 4 years      
Stock options | Grants outside of 2000 and 2017 Plans                        
Class of Stock [Line Items]                        
Options outstanding (in shares)                   88,930    
Portion vesting one year after the issuance date (as a percent)                 25.00%      
Portion vesting on first day of each month after one year from the issuance date (as a percent)                 2.083%      
Expiration Term                 10 years      
Vesting period                 4 years      
Restricted stock units                        
Class of Stock [Line Items]                        
Restricted stock units outstanding (in shares)               2,011,611 2,011,611 316,709    
Restricted stock units | Grants outside of 2000 and 2017 Plans                        
Class of Stock [Line Items]                        
Restricted stock units outstanding (in shares)                   14,820    
Series B Junior Participating Preferred Stock                        
Stockholder Rights Plan                        
Preferred share purchase right ratio       1                
Preferred stock conversion basis       0.001                
Preferred stock, par value (in dollars per share) | $ / shares       $ 0.001                
Purchase price (in dollars per share) | $ / shares       $ 8.76                
Period following public announcement of beneficial ownership acquired by various persons resulting in rights becoming exercisable       10 days                
Period following commencement of tender offer or exchange offer that would result in acquisition of beneficial ownership various persons resulting in rights becoming exercisable       10 days                
Preferred stock dividend minimum if declared | $ / shares       $ 1.00                
Preferred stock rights ratio over common stock       1,000                
Number of votes per share | Vote       1,000                
Ratio of consideration received in event of conversion or exchange transaction       1,000                
Series B Junior Participating Preferred Stock | Minimum                        
Stockholder Rights Plan                        
Beneficial ownership of common stock (as a percent)       4.99%