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, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Basic
Net income	$ 62,091	$ 33,959	$ 81,981	$ 85,815	$ 25,212	$ 41,835	$ 66,615	$ 70,224	$ 263,846	$ 203,886	$ 317,903
Weighted average shares outstanding-basic (shares)									36,956,115	36,709,940	37,778,304
Basic earnings per common share (in Dollars per share)	$ 1.68	$ 0.92	$ 2.22	$ 2.33	$ 0.69	$ 1.14	$ 1.82	$ 1.92	$ 7.14	$ 5.55	$ 8.41
Diluted
Plus effect of stock options and restricted stock units (shares)									229,713	265,447	353,795
Weighted-average shares outstanding-diluted (shares)									37,185,828	36,975,387	38,132,099
Diluted earnings per common share (in Dollars per share)	$ 1.67	$ 0.91	$ 2.21	$ 2.31	$ 0.68	$ 1.13	$ 1.80	$ 1.90	$ 7.10	$ 5.51	$ 8.34