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Stockholders' Equity - Fair Value of Employee Stock Options (Detail) - $ / shares
3 Months Ended 9 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Dividend yield 0.00% 0.00% 0.00% 0.00%
Volatility 73.07% 80.71% 72.99% 76.86%
Risk-free interest rate 2.79% 2.15% 2.75% 1.81%
Expected life of options 6 years 6 years 6 years 6 years
Weighted average grant date fair value $ 0.67 $ 1.04 $ 0.84 $ 1.73