Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Current tax expense
Federal	$ 41,300	$ 58,273	$ 49,593
State	5,693	8,959	7,093
Current income tax expense (benefit)	46,993	67,232	56,686
Deferred tax expense	45,190	55,492	44,711
Total income tax expense	$ 92,183	$ 122,724	$ 101,397