Business, Basis of Presentation and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2021	Apr. 30, 2021
General liability
Loss contingencies
Deductible amount	$ 500
Primary layer of insurance coverage	300
Workers' compensation
Loss contingencies
Deductible amount	1,000
Primary layer of insurance coverage	500
Automobile
Loss contingencies
Deductible amount	2,500
Primary layer of insurance coverage	1,000
General liability, workers' compensation and automobile | Other accrued expenses and current liabilities.
Loss contingencies
Medical self‑insurance	3,736	$ 3,852
General liability, automobile and workers’ compensation	18,146	19,807
General liability, workers' compensation and automobile | Prepaid expenses and other current assets
Loss contingencies
Expected recoveries for insurance liabilities	(3,208)	$ (3,209)
General liability, workers' compensation and automobile | Minimum
Loss contingencies
Buffer layer of insurance coverage	5,000
Excess layer of insurance coverage	10,000
General liability, workers' compensation and automobile | Maximum
Loss contingencies
Primary layer of insurance coverage	5,000
Buffer layer of insurance coverage	10,000
Excess layer of insurance coverage	$ 100,000