Preferred and Common Stock - Schedule of Stock Options Activity (Details) - $ / shares	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Number of option shares
Ending balance (in shares)	222,050
Stock Options
Number of option shares
Beginning balance (in shares)	291,200	401,800	712,024
Granted (in shares)	0	0	0
Exercised (in shares)	(69,150)	(108,100)	(310,224)
Forfeited (in shares)	0	(2,500)	0
Ending balance (in shares)	222,050	291,200	401,800
Weighted average option exercise price
Beginning balance (in Dollars per share)	$ 37.46	$ 36.55	$ 36.73
Granted (in Dollars per share)	0.00	0.00	0.00
Exercised (in Dollars per share)	34.08	34.37	36.96
Forfeited (in Dollars per share)	0.00	25.26	0.00
Ending balance (in Dollars per share)	$ 38.51	$ 37.46	$ 36.55