Business, Basis of Presentation and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2018	Apr. 30, 2017
Other accrued expenses and current liabilities.
Insurance Liabilities
Aggregate liabilities for medical self-insurance		$ 4.1	$ 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
Deductible amount on insured claim	$ 0.5
Insurance recoveries	$ 26.3
General liability, workers' compensation and automobile | Other accrued expenses and current liabilities.
Insurance Liabilities
Reserve for insurance		14.7	15.9
General liability, workers' compensation and automobile | Prepaid expenses and other current assets
Insurance Liabilities
Insurance recovery receivable		4.8	$ 6.7
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