Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Tax Credit Carryforward [Line Items]
Deferred tax assets, valuation allowance	$ 88,015,000	$ 55,812,000
Deferred tax assets, increase in valuation allowance	32,200,000
Unrecognized tax benefits, if recognized, would impact effective income tax rate	0
Unrecognized tax benefits, cumulative interest and penalties	0	0
Unrecognized tax benefits, anticipated significant change over the next 12 months	0
Federal
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	308,300,000	168,600,000
Tax credit carryforwards, subject to expiration	1,000,000.0
Federal | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	5,400,000
Federal | Charitable Contribution Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	14,300,000
State
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	139,700,000	$ 73,200,000
Tax credit carryforwards, subject to expiration	400,000
State | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 5,300,000