Net Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 21,661	$ 15,158
Denominator for basic net earnings per common share - weighted-average shares	16,264,380	16,180,860
Effect of dilutive securities:
Stock options and restricted stock units	117,000	240,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,380,983	16,421,230
Net earnings per share
Basic (in usd per share)	$ 1.33	$ 0.94
Diluted (in usd per share)	$ 1.32	$ 0.92