Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Apr. 30, 2023	Apr. 30, 2022
Tax Credit Carryforward [Line Items]
Deferred tax assets, valuation allowance	$ 180,571,000	$ 144,678,000
Deferred tax assets, increase in valuation allowance	35,900,000
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	487,600,000	486,200,000
Tax credit carryforwards, subject to expiration	1,000,000.0
Federal | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	12,600,000
Federal | Charitable Contribution Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	25,600,000
State
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	187,800,000	$ 180,400,000
Tax credit carryforwards, subject to expiration	400,000
State | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 10,200,000