Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 240,923	$ 218,632	$ 256,292	$ 231,198	$ 206,892	$ 188,963	$ 217,693	$ 211,917	$ 947,045	$ 825,465	$ 726,515
Gross profit	48,871	44,598	56,052	50,173	43,320	35,117	36,981	37,114	199,694	152,532	124,177
Income before income taxes	20,849	18,683	28,533	23,721	18,035	10,976	12,322	13,054	91,786	54,387	33,670
Net income	$ 13,372	$ 12,013	$ 18,180	$ 15,158	$ 11,308	$ 7,282	$ 7,671	$ 9,238	$ 58,723	$ 35,499	$ 20,461
Earnings per share
Basic (usd per share)	$ 0.82	$ 0.74	$ 1.12	$ 0.94	$ 0.71	$ 0.46	$ 0.49	$ 0.59	$ 3.61	$ 2.25	$ 1.34
Diluted (usd per share)	$ 0.81	$ 0.73	$ 1.10	$ 0.92	$ 0.69	$ 0.45	$ 0.48	$ 0.59	$ 3.57	$ 2.21	$ 1.31