Share-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Jan. 31, 2021 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares shares
Number of Stock Options Outstanding
Balance at beginning of period (in shares) | shares	32,877
Options granted (in shares) | shares	14,415
Options exercised (in shares) | shares	(4,563)
Options cancelled (in shares) | shares	(2,559)
Balance at end of period (in shares) | shares	40,170	32,877
Vested and exercisable at end of period (in shares) | shares	12,799
Vested and expected to vest at end of period (in shares) | shares	41,161
Weighted Average Exercise Price
Balance at beginning of period (in dollars per share) | $ / shares	$ 3.48
Options granted (in dollars per share) | $ / shares	11.12
Options exercised (in dollars per share) | $ / shares	3.06
Options cancelled (in dollars per share) | $ / shares	5.55
Balance at end of period (in dollars per share) | $ / shares	6.13	$ 3.48
Vested and exercisable at end of period (in dollars per share) | $ / shares	3.01
Vested and expected to vest at end of period (in dollars per share) | $ / shares	$ 6.12
Weighted Average Remaining Contractual Life (years)
Balance at beginning of period	8 years 18 days	8 years 10 days
Balance at end of period	8 years 18 days	8 years 10 days
Vested and exercisable at end of period	6 years 5 months 12 days
Vested and expected to vest at end of period	8 years 25 days
Aggregate Intrinsic Value
Balance at beginning of period | $	$ 449,073	$ 116,962
Balance at end of period | $	449,073	$ 116,962
Vested and exercisable at end of period | $	180,395
Vested and expected to vest at end of period | $	$ 460,444