Preferred and Common Stock - Schedule of Stock Options Activity (Details) - $ / shares	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Number of option shares
Ending balance (in shares)	181,673
Stock Options
Number of option shares
Beginning balance (in shares)	222,050	291,200	401,800
Granted (in shares)	0	0	0
Exercised (in shares)	(40,377)	(69,150)	(108,100)
Forfeited (in shares)	0	0	(2,500)
Ending balance (in shares)	181,673	222,050	291,200
Weighted average option exercise price
Beginning balance (in Dollars per share)	$ 38.51	$ 37.46	$ 36.55
Granted (in Dollars per share)	0.00	0.00	0.00
Exercised (in Dollars per share)	34.11	34.08	34.37
Forfeited (in Dollars per share)	0.00	0.00	25.26
Ending balance (in Dollars per share)	$ 39.48	$ 38.51	$ 37.46