Business, Basis of Presentation and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Millions	Jul. 31, 2020	Apr. 30, 2020
Other accrued expenses and current liabilities.
Insurance Liabilities
Aggregate liabilities for medical self-insurance	$ 4.1	$ 3.8
General liability
Insurance Liabilities
Deductible amount	0.3
Primary layer of insurance coverage	0.3
Workers' compensation
Insurance Liabilities
Deductible amount	0.5
Primary layer of insurance coverage	0.5
Automobile
Insurance Liabilities
Deductible amount	1.0
Primary layer of insurance coverage	1.0
General liability, workers' compensation and automobile | Other accrued expenses and current liabilities.
Insurance Liabilities
Reserve for insurance	18.1	19.4
General liability, workers' compensation and automobile | Prepaid expenses and other current assets
Insurance Liabilities
Insurance recovery receivable	6.4	$ 6.0
General liability, workers' compensation and automobile | Minimum
Insurance Liabilities
Buffer layer of insurance coverage	5.0
Excess layer of insurance coverage	10.0
General liability, workers' compensation and automobile | Maximum
Insurance Liabilities
Primary layer of insurance coverage	5.0
Buffer layer of insurance coverage	10.0
Excess layer of insurance coverage	$ 100.0