Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Computation of basic and diluted earnings per share of common stock
Net income	$ (41,456)	$ 10,879	$ 29,138	$ 24,820	$ 16,625	$ 5,815	$ 24,912	$ 8,650	$ 23,381		$ 56,002		$ 62,971
Less: Net income allocated to participating securities									74		1,382
Net income attributable to common stockholders									$ 23,307		$ 54,620		$ 62,971
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)	42,435	42,223	41,761	41,001	40,487	40,912	41,149	41,094	41,853		40,914		41,015
Basic earnings per common share (in dollars per share)	$ (0.98)	$ 0.26	$ 0.70	$ 0.60	$ 0.40	$ 0.14	$ 0.59	$ 0.21	$ 0.56	[1]	$ 1.33	[1]	$ 1.54	[1]
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)	42,435	42,223	41,761	41,001	40,487	40,912	41,149	41,094	41,853		40,914		41,015
Add: Common Stock Equivalents									651		675		1,148
Diluted weighted average common shares outstanding (in shares)	42,435	42,949	42,635	41,615	40,976	41,371	41,918	42,074	42,504		41,589		42,163
Diluted earnings per common share (in dollars per share)	$ (0.98)	$ 0.25	$ 0.68	$ 0.59	$ 0.39	$ 0.14	$ 0.58	$ 0.20	$ 0.55	[1]	$ 1.31	[1]	$ 1.49	[1]
Shares were not included in the calculation of Diluted loss per common share
Anti-dilutive shares									800		600

[1] See Note 19 for detailed calculations.