Federal, State and Local Income Taxes - Provision for income taxes differs from the amount of income tax determined by applying the applicable U.S. statutory income tax rate (Details 2)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
U.S. statutory federal rate	35.00%	35.00%	35.00%
Increase (decrease) in tax rate from:
State and local income taxes, net of federal income tax benefit	(0.15%)	0.84%	2.96%
Effect of dividends received deductions	(0.40%)	(0.33%)	(0.27%)
Write off goodwill	(1.62%)
Domestic production tax credit	(0.44%)	(0.58%)	(0.52%)
Other, net	(1.87%)	(1.43%)	(0.17%)
Effective income tax rate	30.52%	33.50%	37.00%