Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Computation of basic and diluted earnings (loss) per share of common stock
Net income (loss)									$ 48,886	$ 12,564	$ (11,697)
Basic earnings (loss) per common share:
Basic weighted average shares outstanding per common share (in shares)	40,955,632	40,942,905	40,942,905	38,200,597	32,892,905	32,890,930	32,737,956	32,677,418	40,260,405	32,799,098	32,450,401
Basic earnings (loss) per common share (in dollars per share)	$ 0.35	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.21	$ 0.38	$ (0.36)
Diluted earnings (loss) per common share:
Basic weighted average shares outstanding per common share (in shares)	40,955,632	40,942,905	40,942,905	38,200,597	32,892,905	32,890,930	32,737,956	32,677,418	40,260,405	32,799,098	32,450,401
Add: Shares of common stock assumed issued upon exercise of stock options (in shares)									809,620	326,144
Diluted weighted average shares outstanding per common share (in shares)	41,758,974	41,577,675	41,319,651	38,602,378	33,155,140	32,890,930	32,898,075	32,830,677	41,070,025	33,125,242	32,450,401
Diluted earnings (loss) per common share (in dollars per share)	$ 0.33	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.19	$ 0.38	$ (0.36)
Shares were not included in the calculation of Diluted loss per common share
Anti-dilutive shares											10,417