Contingencies (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2017 USD ($) lawsuit state	Apr. 30, 2016 USD ($)
Loss Contingency [Abstract]
Accrued environmental liability	$ 283	$ 341
Loss Contingencies
Annual stop loss limit	1,000
Letters of credit outstanding	21,126	20,115
Investments In escrow for insurance	$ 223
Number of states that require partial self-insurance | state	1
Self-insurance reserves	$ 37,984	$ 35,535
Motor Fuel Temperature Sales Practices (Hot Fuel)
Loss Contingencies
Number of lawsuits | lawsuit	4