Quarterly report pursuant to Section 13 or 15(d)

Description of Stock Plans - Summary of Stock Option Activity (Details)

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Description of Stock Plans - Summary of Stock Option Activity (Details) - Stock Option - USD ($)
$ / shares in Units, $ in Thousands
9 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Mar. 31, 2018
Number of Shares (in shares)      
Beginning Balance (in shares) 9,741,969    
Granted (in shares) 1,349,925 1,338,778  
Forfeited / Cancelled (in shares) (1,239,335)    
Exercised (in shares) (316,784)    
Ending Balance (in shares) 9,535,775   9,741,969
Vested and expected to vest (net of estimated forfeitures) (in shares) 8,338,785    
Exercisable (in shares) 5,007,381    
Weighted Average Exercise Price ($ per share)      
Options outstanding (in dollars per share) $ 2.08    
Granted (in dollars per share) 1.64    
Forfeited/Cancelled (in dollars per share) 4.20    
Exercised (in dollars per share) 0.92    
Options outstanding (in dollars per share) 1.78   $ 2.08
Vested and expected to vest (net of estimated forfeitures) (in dollars per share) 1.85    
Exercisable (in dollars per share) $ 2.27    
Weighted Average Remaining Contractual Life (in years)      
Outstanding 7 years 6 months 10 days   7 years 9 months 26 days
Vested and expected to vest (net of estimated forfeitures) 7 years 4 months 14 days    
Exercisable, December 31, 2018 6 years 8 months 14 days    
Aggregate Intrinsic Value (in thousands)      
Outstanding $ 4,590   $ 6,286
Vested and expected to vest (net of estimated forfeitures) 3,894    
Exercisable, December 31, 2018 $ 1,719