Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Current tax expense
Federal	$ 49,593	$ 44,078	$ 23,519
State	7,093	5,657	4,455
Current income tax expense (benefit)	56,686	49,735	27,974
Deferred tax expense	44,711	17,089	31,828
Total income tax expense	$ 101,397	$ 66,824	$ 59,802