Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Components of income tax expense (benefit)
Current federal	$ 30,827	$ 37,164	$ 28,043
Current state	6,409	5,875	5,162
Total current	37,236	43,039	33,205
Deferred federal	(14,796)	(19,011)	(19,993)
Deferred state	(1,557)	(1,374)	(628)
Total deferred	(16,353)	(20,385)	(20,621)
Total provision for income taxes	$ 20,883	$ 22,654	$ 12,584