Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Computation of basic and diluted earnings per share of common stock
Net income	$ 17,224	$ 2,825	$ 26,387	$ 5,836
Basic earnings per common share:
Basic weighted average shares outstanding per common share (in shares)	40,942,905	32,737,956	39,579,244	32,707,297
Basic earnings per common share (in dollars per share)	$ 0.42	$ 0.09	$ 0.67	$ 0.18
Diluted earnings per common share:
Basic weighted average shares outstanding per common share (in shares)	40,942,905	32,737,956	39,579,244	32,707,297
Add: Shares of common stock assumed issued upon exercise of stock options (in shares)	376,746	160,119	376,746	208,574
Diluted weighted average shares outstanding per common share (in shares)	41,319,651	32,898,075	39,955,990	32,915,871
Diluted earnings per common share (in dollars per share)	$ 0.42	$ 0.09	$ 0.66	$ 0.18