Net Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 22,281	$ 21,661
Denominator for basic net earnings per common share - weighted-average shares	16,271,788	16,264,380
Effect of dilutive securities:
Stock options and restricted stock units	83,000	117,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,355,045	16,380,983
Net earnings per share
Basic (in usd per share)	$ 1.37	$ 1.33
Diluted (in usd per share)	$ 1.36	$ 1.32