Net Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 22,163	$ 26,881	$ 18,488	$ 24,767	$ 49,044	$ 43,255
Denominator for basic net earnings per common share - weighted-average shares	16,919,664		17,555,584		16,892,267	17,544,849
Effect of dilutive securities:
Stock options and restricted stock units	36,000		32,000		40,000	45,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,955,835		17,588,449		16,932,236	17,589,767
Net earnings per share
Basic (in usd per share)	$ 1.31		$ 1.05		$ 2.90	$ 2.47
Diluted (in usd per share)	$ 1.31		$ 1.05		$ 2.90	$ 2.46