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, 2019	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017	Jan. 31, 2019	Jan. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 18,409	$ 24,767	$ 1,996	$ 22,281	$ 61,664	$ 44,032
Denominator for basic net earnings per common share - weighted-average shares	17,186,456		16,578,235		17,425,385	16,349,716
Effect of dilutive securities:
Stock options and restricted stock units	30,000		113,000		42,000	112,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	17,216,327		16,690,760		17,466,936	16,461,509
Net earnings per share
Basic (in usd per share)	$ 1.07		$ 0.12		$ 3.54	$ 2.69
Diluted (in usd per share)	$ 1.07		$ 0.12		$ 3.53	$ 2.67