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, 2018	Jul. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 18,488	$ 24,767	$ 19,755	$ 22,281	$ 43,255	$ 42,036
Denominator for basic net earnings per common share - weighted-average shares	17,555,584		16,197,088		17,544,849	16,234,746
Effect of dilutive securities:
Stock options and restricted stock units	32,000		71,000		45,000	84,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	17,588,449		16,268,078		17,589,767	16,319,224
Net earnings per share
Basic (in usd per share)	$ 1.05		$ 1.22		$ 2.47	$ 2.59
Diluted (in usd per share)	$ 1.05		$ 1.21		$ 2.46	$ 2.58