Stock-Based Compensation - Summary of stock option activity (Detail) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) $ / shares shares
Number of options
Number of options, beginning balance | shares	3,873,888
Number of options, granted | shares	2,290,978
Number of options, exercised | shares	(42,213)
Number of options, forfeited | shares	(61,738)
Number of options, canceled | shares	(226,233)
Number of options, ending balance | shares	5,834,682	3,873,888
Weighted- Average Exercise Price
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 8.33
Weighted average exercise price, granted (in dollars per share) | $ / shares	23.51
Weighted average exercise price, exercised (in dollars per share) | $ / shares	4.31
Weighted average exercise price, forfeited (in dollars per share) | $ / shares	14.86
Weighted average exercise price, canceled (in dollars per share) | $ / shares	7.86
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	$ 14.27	$ 8.33
Additional Disclosures
Remaining contractual term	9 years 2 months 15 days	9 years 4 months 13 days
Aggregate intrinsic value | $	$ 122,505	$ 28,029
Number of options, exercisable | shares	945,851
Weighted average exercise price, exercisable (in dollars per share) | $ / shares	$ 8.08
Remaining contractual term, exercisable	8 years 8 months 26 days
Aggregate intrinsic value, exercisable | $	$ 25,646