Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 22, 2017	Apr. 30, 2020	Apr. 30, 2019
Income Tax Contingency [Line Items]
Additional valuation allowance deferred income tax assets		$ 29,000
Tax reform, accounting complete	false
Tax reform, measurement period from enactment date	1 year
Effective income tax rate, provisions (benefit)		(2.10%)	35.90%
Undistributed earnings of foreign subsidiary		$ 84,000,000
Gross tax-effected unrecognized tax benefits		0	$ 0
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards		0
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards		17,700,000	17,900,000
Tax credit carryforwards		2,900,000	2,900,000
Valuation allowances for net operating loss carryforward		904,000	911,000
Valuation allowances for tax credits		$ 2,300,000	$ 2,300,000
State | Minimum
Income Tax Contingency [Line Items]
Operating loss carry forwards expiration dates			Apr. 30, 2025
State tax credit carryforwards expire date			Apr. 30, 2023
State | Maximum
Income Tax Contingency [Line Items]
Operating loss carry forwards expiration dates			Apr. 30, 2038
State tax credit carryforwards expire date			Apr. 30, 2025