Preferred and Common Stock - Schedule of Stock Options Activity (Details) - $ / shares	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Number of option shares
Ending balance (in shares)	401,800
Stock Options
Number of option shares
Beginning balance (in shares)	712,024	854,809	1,053,509
Granted	0	0	0
Exercised	(310,224)	(140,785)	(198,200)
Forfeited	0	(2,000)	(500)
Ending balance (in shares)	401,800	712,024	854,809
Weighted average option exercise price
Beginning balance (in Dollars per share)	$ 36.73	$ 34.64	$ 32.59
Granted	0.00	0.00	0.00
Exercised	36.96	23.93	23.82
Forfeited	0.00	44.39	14.08
Ending balance (in Dollars per share)	$ 36.55	$ 36.73	$ 34.64