Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Computation of basic and diluted earnings (loss) per share of common stock
Net income (loss)	$ 8,227	$ (2,212)	$ 34,614	$ 3,624
Basic earnings (loss) per common share:
Basic weighted average shares outstanding per common share (in shares)	40,942,905	32,890,930	40,035,450	32,768,418
Basic earnings (loss) per common share (in dollars per share)	$ 0.20	$ (0.07)	$ 0.86	$ 0.11
Diluted earnings (loss) per common share:
Basic weighted average shares outstanding per common share (in shares)	40,942,905	32,890,930	40,035,450	32,768,418
Add: Shares of common stock assumed issued upon exercise of stock options (in shares)	634,770		634,770	218,752
Diluted weighted average shares outstanding per common share (in shares)	41,577,675	32,890,930	40,670,220	32,987,170
Diluted earnings (loss) per common share (in dollars per share)	$ 0.20	$ (0.07)	$ 0.85	$ 0.11
Shares were not included in the calculation of Diluted loss per common share
Anti-dilutive shares		218,752