Business, Basis of Presentation and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Millions	Jan. 31, 2020	Apr. 30, 2019
Other accrued expenses and current liabilities.
Insurance Liabilities
Aggregate liabilities for medical self-insurance	$ 4.0	$ 3.4
General liability
Insurance Liabilities
Deductible amount	0.3
Workers' compensation
Insurance Liabilities
Deductible amount	0.5
Automobile
Insurance Liabilities
Deductible amount	1.0
General liability, workers' compensation and automobile | Other accrued expenses and current liabilities.
Insurance Liabilities
Reserve for insurance	19.1	17.7
General liability, workers' compensation and automobile | Prepaid expenses and other current assets
Insurance Liabilities
Insurance recovery receivable	6.1	$ 6.0
General liability, workers' compensation and automobile | Minimum
Insurance Liabilities
Primary layer of insurance coverage	0.5
Excess layer of insurance coverage	2.0
General liability, workers' compensation and automobile | Maximum
Insurance Liabilities
Primary layer of insurance coverage	2.0
Excess layer of insurance coverage	$ 100.0