Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Computation of basic and diluted earnings per share of common stock
Net income	$ 19,686	$ 8,227	$ 53,052	$ 34,614
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)	41,036	40,943	41,004	40,035
Basic earnings per common share (in dollars per share)	$ 0.48	$ 0.20	$ 1.29	$ 0.86
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)	41,036	40,943	41,004	40,035
Add: Common Stock Equivalents	1,192	635	1,163	635
Diluted weighted average common shares outstanding (in shares)	42,228	41,578	42,167	40,670
Diluted earnings per common share (in dollars per share)	$ 0.47	$ 0.20	$ 1.26	$ 0.85