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, 2020	Jul. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 22,256	$ 16,485	$ 22,163	$ 26,881	$ 38,741	$ 49,044
Denominator for basic net earnings per common share - weighted-average shares	16,992,297		16,919,664		16,964,565	16,892,267
Effect of dilutive securities:
Stock options and restricted stock units	55,000		36,000		72,000	40,000
Diluted (in shares)	17,047,296		16,955,835		17,036,652	16,932,236
Net earnings per share
Basic (in usd per share)	$ 1.31		$ 1.31		$ 2.28	$ 2.90
Diluted (in usd per share)	$ 1.31		$ 1.31		$ 2.27	$ 2.90