Basis of Presentation, Business and Summary of Significant Accounting Policies - Insurance Liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2016	Apr. 30, 2016	Jul. 31, 2015
Other accrued expenses and current liabilities
Insurance Liabilities
Medical self-insurance	$ 3,272	$ 3,342
General Liability
Insurance Liabilities
Deductible amount	250
Workers' Compensation
Insurance Liabilities
Deductible amount	500
Automobile
Insurance Liabilities
Deductible amount	1,000
General Liability, Workers' Compensation and Automobile
Insurance Liabilities
Reserve for insurance	12,419	12,213
Insurance recovery receivable	4,993	$ 4,832	$ 26,000
General Liability, Workers' Compensation and Automobile | Minimum
Insurance Liabilities
Primary layer of stop loss coverage	500
Excess layer of stop loss coverage	2,000
General Liability, Workers' Compensation and Automobile | Maximum
Insurance Liabilities
Primary layer of stop loss coverage	2,000
Excess layer of stop loss coverage	$ 100,000