Net Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 12,804	$ 22,163	$ 26,881	$ 18,409	$ 18,488	$ 24,767	$ 61,848	$ 61,664
Denominator for basic net earnings per common share - weighted-average shares	16,922,231			17,186,456			16,902,255	17,425,385
Effect of dilutive securities:
Stock options and restricted stock units	53,000			30,000			45,000	42,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,974,956			17,216,327			16,947,449	17,466,936
Net earnings per share
Basic (in usd per share)	$ 0.76			$ 1.07			$ 3.66	$ 3.54
Diluted (in usd per share)	$ 0.75			$ 1.07			$ 3.65	$ 3.53