Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Computation of basic and diluted earnings per share of common stock
Net income	$ 5,815	$ 19,686	$ 39,377	$ 53,052
Less: Net income allocated to participating securities	156		940
Net income attributable to common stockholders	$ 5,659	$ 19,686	$ 38,437	$ 53,052
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)	40,912	41,036	41,053	41,004
Basic earnings per common share (in dollars per share)	$ 0.14	$ 0.48	$ 0.94	$ 1.29
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)	40,912	41,036	41,053	41,004
Add: Common Stock Equivalents	459	1,192	736	1,163
Diluted weighted average common shares outstanding (in shares)	41,371	42,228	41,789	42,167
Diluted earnings per common share (in dollars per share)	$ 0.14	$ 0.47	$ 0.92	$ 1.26