Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Income Tax Disclosure [Abstract]
Income taxes at the statutory rates	35.00%	35.00%	35.00%
Federal tax credits	(1.70%)	(2.10%)	(1.80%)
State income taxes, net of federal tax benefit	3.10%	3.20%	2.40%
Out of period adjustments	0.00%	(1.40%)	0.00%
Other	(0.40%)	(0.20%)	1.00%
Effective income tax rate (percent)	36.00%	34.50%	36.60%