Preferred and Common Stock - Schedule of Stock Options Activity (Details) - $ / shares	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Number of option shares
Ending balance (in shares)	291,200
Stock Options
Number of option shares
Beginning balance (in shares)	401,800	712,024	854,809
Granted (in shares)	0	0	0
Exercised (in shares)	(108,100)	(310,224)	(140,785)
Forfeited (in shares)	(2,500)	0	(2,000)
Ending balance (in shares)	291,200	401,800	712,024
Weighted average option exercise price
Beginning balance (in Dollars per share)	$ 36.55	$ 36.73	$ 34.64
Granted (in Dollars per share)	0.00	0.00	0.00
Exercised (in Dollars per share)	34.37	36.96	23.93
Forfeited (in Dollars per share)	25.26	0.00	44.39
Ending balance (in Dollars per share)	$ 37.46	$ 36.55	$ 36.73