Net Income Per Common Share - Schedule of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Basic
Net income	$ 47,044	$ 38,099	$ 79,033	$ 61,806	$ 41,343	$ 39,319	$ 49,869	$ 50,097	$ 225,982	$ 180,628	$ 126,820
Weighted average shares outstanding-basic									39,016,299	38,743,227	38,457,680
Basic earnings per common share (in Dollars per share)	$ 1.20	$ 0.98	$ 2.03	$ 1.59	$ 1.06	$ 1.01	$ 1.29	$ 1.30	$ 5.79	$ 4.66	$ 3.30
Diluted
Plus effect of stock options and restricted stock units									405,900	360,606	410,726
Weighted-average shares outstanding-diluted									39,422,199	39,103,833	38,868,406
Diluted earnings per common share (in Dollars per share)	$ 1.19	$ 0.97	$ 2.00	$ 1.57	$ 1.05	$ 1.01	$ 1.28	$ 1.28	$ 5.73	$ 4.62	$ 3.26