Net Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 24,767	$ 22,281
Denominator for basic net earnings per common share - weighted-average shares	17,534,114	16,271,788
Effect of dilutive securities:
Stock options and restricted stock units	85,000	83,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	17,618,943	16,355,045
Net earnings per share
Basic (in usd per share)	$ 1.41	$ 1.37
Diluted (in usd per share)	$ 1.41	$ 1.36