Annual report pursuant to Section 13 and 15(d)

Description of Stock Plans - Summary of Options Granted under all Equity Plans (Detail)

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Description of Stock Plans - Summary of Options Granted under all Equity Plans (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Number of Shares      
Forfeited/Canceled (shares) (2,381,302)    
Stock Option      
Number of Shares      
Beginning Balance (shares) 7,824,395 5,789,758  
Granted (shares) 4,271,523 3,959,150 3,124,200
Forfeited/Canceled (shares) (2,378,523) (1,857,830)  
Exercised (shares) 18,383 (66,683)  
Ending Balance (shares) 9,735,778 7,824,395 5,789,758
Vested and expected to vest (shares) 7,167,283    
Exercisable (shares) 3,557,304    
Weighted Average Exercise Price (per share)      
Beginning Balance ($ per share) $ 3.61 $ 4.65  
Granted ($ per share) 0.82 2.05  
Forfeited/Canceled ($ per share) 2.90 3.37  
Exercised ($ per share) 0.64 0.77  
Ending Balance ($ per share) 2.56 $ 3.61 $ 4.65
Vested and expected to vest (net of estimated forfeitures) ($ per share) 3.09    
Exercisable ($ per share) $ 4.75    
Weighted Average Remaining Contractual Life (in years)      
Outstanding 7 years 11 months 12 days 8 years 2 months 27 days 8 years 4 months 6 days
Vested and expected to vest (net of estimated forfeitures) 7 years 5 months 9 days    
Exercisable, March 31, 2017 5 years 9 months 15 days    
Aggregate Intrinsic Value (in thousands)      
Balance $ 801 $ 110 $ 1,319
Vested and expected to vest (net of estimated forfeitures) 422    
Exercisable, March 31, 2017 $ 57