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, 2015	Apr. 30, 2014	Apr. 30, 2013
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 206,892	$ 188,963	$ 217,693	$ 211,917	$ 188,855	$ 169,033	$ 190,532	$ 178,095	$ 825,465	$ 726,515	$ 630,437
Gross profit	43,320	35,117	36,981	37,114	32,187	26,001	32,274	33,715	152,532	124,177	102,656
Income before income taxes	18,035	10,976	12,322	13,054	9,404	4,953	8,631	10,682	54,387	33,670	16,740
Net income	$ 11,308	$ 7,282	$ 7,671	$ 9,238	$ 5,634	$ 2,901	$ 5,271	$ 6,655	$ 35,499	$ 20,461	$ 9,758
Earnings per share
Basic (usd per share)	$ 0.71	$ 0.46	$ 0.49	$ 0.59	$ 0.36	$ 0.19	$ 0.35	$ 0.45	$ 2.25	$ 1.34	$ 0.67
Diluted (usd per share)	$ 0.69	$ 0.45	$ 0.48	$ 0.59	$ 0.36	$ 0.18	$ 0.34	$ 0.43	$ 2.21	$ 1.31	$ 0.66