Basis of Presentation, Business and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Apr. 30, 2017
Other accrued expenses and current liabilities
Insurance Liabilities
Medical self-insurance	$ 4,295	$ 3,429
General Liability
Insurance Liabilities
Deductible amount	250
Workers' Compensation
Insurance Liabilities
Deductible amount	500
Automobile
Insurance Liabilities
Deductible amount	1,000
General liability, automobile and workers' compensation
Insurance Liabilities
Reserve for insurance	17,207	15,934
Insurance recovery receivable	8,298	$ 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