Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Computation of basic and diluted earnings per share of common stock
Net income		$ 29,138	$ 24,912	$ 53,958	$ 33,562
Less: Net income allocated to participating securities			665	342	751
Net income attributable to common stockholders		$ 29,138	$ 24,247	$ 53,616	$ 32,811
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)		41,761	41,149	41,382	41,121
Basic earnings per common share (in dollars per share)	[1]	$ 0.70	$ 0.59	$ 1.30	$ 0.80
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)		41,761	41,149	41,382	41,121
Add: Common Stock Equivalents		874	769	744	875
Diluted weighted average common shares outstanding (in shares)		42,635	41,918	42,126	41,996
Diluted earnings per common share (in dollars per share)	[1]	$ 0.68	$ 0.58	$ 1.27	$ 0.78

[1] See Note 15 for detailed calculations