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, 2015	Oct. 31, 2014	Oct. 31, 2015	Oct. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 18,180	$ 7,671	$ 33,338	$ 16,909
Denominator for basic net earnings per common share - weighted-average shares	16,282,881	15,672,198	16,231,870	15,602,150
Effect of dilutive securities:
Stock options and restricted stock units	189,764	288,038	215,067	262,410
Denominator for diluted net earnings per common share - weighted-average shares and assumed conversions	16,472,645	15,960,236	16,446,937	15,864,560
Net earnings per share
Basic (in usd per share)	$ 1.12	$ 0.49	$ 2.05	$ 1.08
Diluted (in usd per share)	$ 1.10	$ 0.48	$ 2.03	$ 1.07