Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Computation of basic and diluted earnings per share of common stock
Net income	$ 24,912	$ 18,023	$ 33,562	$ 33,366
Less: Net income allocated to participating securities	665		751
Net income attributable to common stockholders	$ 24,247	$ 18,023	$ 32,811	$ 33,366
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)	41,149	41,006	41,121	40,988
Basic earnings per common share (in dollars per share)	$ 0.59	$ 0.44	$ 0.80	$ 0.81
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)	41,149	41,006	41,121	40,988
Add: Common Stock Equivalents	769	1,140	875	1,149
Diluted weighted average common shares outstanding (in shares)	41,918	42,146	41,996	42,137
Diluted earnings per common share (in dollars per share)	$ 0.58	$ 0.43	$ 0.78	$ 0.79