Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Computation of basic and diluted earnings per share of common stock
Net income	$ 15,343	$ 9,163
Basic earnings per common share:
Basic weighted average shares outstanding per common share (in shares)	40,970,905	38,200,597
Basic earnings per common share (in dollars per share)	$ 0.37	$ 0.24
Diluted earnings per common share:
Basic weighted average shares outstanding per common share (in shares)	40,970,905	38,200,597
Add: Shares of common stock assumed issued upon exercise of stock options (in shares)	1,156,866	401,781
Diluted weighted average shares outstanding per common share (in shares)	42,127,771	38,602,378
Diluted earnings per common share (in dollars per share)	$ 0.36	$ 0.24