Contingencies (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2018 USD ($) state	Apr. 30, 2017 USD ($)
Loss Contingency [Abstract]
Accrued environmental liability	$ 260	$ 283
Annual stop loss limit	1,000
Letters of credit outstanding	21,118	21,126
Investments In escrow for insurance	$ 224
Number of states that require partial self-insurance | state	1
Self insurance reserve	$ 39,777	$ 37,984