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, 2018
Mar. 31, 2017
Mar. 31, 2016
Number of Shares      
Forfeited/Canceled (in shares) (1,698,906)    
Stock Option      
Number of Shares      
Beginning Balance (in shares) 9,735,778 7,824,395  
Granted (in shares) 1,963,378 4,271,523 3,959,150
Forfeited/Canceled (in shares) (1,698,906) (2,378,523)  
Exercised (in shares) (258,281) 18,383  
Ending Balance (in shares) 9,741,969 9,735,778 7,824,395
Vested and expected to vest (in shares) 8,031,223    
Exercisable (in shares) 4,729,348    
Weighted Average Exercise Price (per share)      
Beginning Balance (in dollars per share) $ 2.56 $ 3.61  
Granted (in dollars per share) 1.53 0.82  
Forfeited/Canceled (in dollars per share) 4.40 2.90  
Exercised (in dollars per share) 1.04 0.64  
Ending Balance (in dollars per share) 2.08 $ 2.56 $ 3.61
Vested and expected to vest (net of estimated forfeitures) (in dollars per share) 2.28    
Exercisable (in dollars per share) $ 3.05    
Weighted Average Remaining Contractual Life (in years)      
Outstanding 7 years 9 months 25 days 7 years 11 months 12 days 8 years 2 months 27 days
Vested and expected to vest (net of estimated forfeitures) 7 years 7 months 2 days    
Exercisable, March 31, 2018 6 years 9 months 22 days    
Aggregate Intrinsic Value (in thousands)      
Balance $ 6,286 $ 801 $ 110
Vested and expected to vest (net of estimated forfeitures) 4,740    
Exercisable, March 31, 2018 $ 1,800