Basis of Presentation, Business and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2017
Other liabilities
Insurance Liabilities
Medical self-insurance	$ 3,342	$ 3,429
General Liability
Insurance Liabilities
Deductible amount		250
Workers' Compensation
Insurance Liabilities
Deductible amount		500
Automobile
Insurance Liabilities
Deductible amount		1,000
Deductible amount on insured claim	500
Insurance recoveries	26,300
General liability, automobile and workers' compensation
Insurance Liabilities
Reserve for insurance	12,213	15,934
Insurance recovery receivable	$ 4,832	6,708
General liability, automobile and workers' compensation | Minimum
Insurance Liabilities
Primary layer of insurance coverage		500
Excess layer of insurance coverage		2,000
General liability, automobile and workers' compensation | Maximum
Insurance Liabilities
Primary layer of insurance coverage		2,000
Excess layer of insurance coverage		$ 100,000