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, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 12,013	$ 7,282	$ 45,351	$ 24,191
Denominator for basic net earnings per common share - weighted-average shares	16,294,889	15,859,533	16,252,876	15,687,944
Effect of dilutive securities:
Stock options and restricted stock units	162,000	272,000	198,000	265,000
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,457,308	16,131,140	16,450,394	15,953,420
Net earnings per share
Basic (in usd per share)	$ 0.74	$ 0.46	$ 2.79	$ 1.54
Diluted (in usd per share)	$ 0.73	$ 0.45	$ 2.76	$ 1.52