Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Components of income tax expense (benefit)
Current federal	$ 37,164	$ 28,043	$ 11,638
Current state	5,875	5,162	2,688
Total current	43,039	33,205	14,326
Deferred federal	(19,011)	(19,993)	(17,492)
Deferred state	(1,374)	(628)	(3,460)
Total deferred	(20,385)	(20,621)	(20,952)
Total provision for (benefit from) income taxes	$ 22,654	$ 12,584	$ (6,626)