Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Income Tax Disclosure [Line Items]
Valuation allowance for deferred tax assets	$ 225,197,000	$ 92,309,000
Net operating loss carryforward	208,629,000	84,194,000
Research and development tax credit carryforwards	15,333,000	3,584,000
Estimated income tax benefit from CARES Act	3,300,000
Unrecognized tax benefits	9,706,000	3,870,000	$ 2,019,000	$ 1,196,000
Unrecognized tax benefits that would impact the effective tax rate before consideration of valuation allowance	0
Unrecognized tax benefit acquired from CARES Act	2,300,000
Unrecognized tax benefit acquired from research and development tax credits	3,600,000
Recognize penalties and interests accrued on unrecognized tax benefits	100,000	100,000	$ 200,000
Accrued interest and penalties, amount	200,000	300,000
Dividend withholding tax from foreign jurisdictions	800,000
GILTI provision	500,000
Canada Revenue Agency
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 600,000
Research and development tax credit carryforwards, expire date	Apr. 30, 2037
Dutch | Tax and Customs Administration, Netherlands
Income Tax Disclosure [Line Items]
Net operating loss carryforward	$ 396,200,000
Net operating loss carryforward, expire date	Apr. 30, 2022
U.S. Federal | IRS
Income Tax Disclosure [Line Items]
Net operating loss carryforward	$ 490,200,000
Net operating loss carryforward, expire date	Apr. 30, 2031
Research and development tax credit carryforwards	$ 11,300,000
Research and development tax credit carryforwards, expire date	Apr. 30, 2030
U.S. Federal | Her Majesty's Revenue and Customs (HMRC)
Income Tax Disclosure [Line Items]
Net operating loss carryforward	$ 18,600,000
U.S. State Income Tax
Income Tax Disclosure [Line Items]
Net operating loss carryforward	$ 416,800,000
Net operating loss carryforward, expire date	Apr. 30, 2024
Research and development tax credit carryforwards	$ 1,300,000
Research and development tax credit carryforwards, expire date	Apr. 30, 2022
The Netherlands
Income Tax Disclosure [Line Items]
Valuation allowance for deferred tax assets	$ 88,400,000	53,100,000
Valuation allowance, net deferred tax assets, jurisdictions increased	35,300,000	10,600,000
United States
Income Tax Disclosure [Line Items]
Valuation allowance for deferred tax assets	132,900,000	38,400,000
Valuation allowance, net deferred tax assets, jurisdictions increased	94,500,000	35,000,000.0
United Kingdom
Income Tax Disclosure [Line Items]
Valuation allowance for deferred tax assets	3,900,000	800,000
Valuation allowance, net deferred tax assets, jurisdictions increased	3,100,000	$ 800,000
Non-U.S. Subsidiaries
Income Tax Disclosure [Line Items]
Cumulative earnings	$ 48,900,000