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, 2021	Jul. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 2,030	$ 2,981	$ 23,122	$ 16,059	$ 5,011	$ 39,181
Denominator for basic net earnings per common share - weighted-average shares	16,567,391		16,992,297		16,614,112	16,964,565
Effect of dilutive securities:
Stock options and restricted stock units	39,000		55,000		49,000	72,000
Diluted (in shares)	16,605,911		17,047,296		16,662,791	17,036,652
Net earnings per share
Basic (in usd per share)	$ 0.12		$ 1.36		$ 0.30	$ 2.31
Diluted (in usd per share)	$ 0.12		$ 1.36		$ 0.30	$ 2.30
Stock excluded from the calculation of net earnings per share (shares)	0		0		0	0