Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Quarterly Financial Data [Abstract]
Net sales	$ 171,079	$ 151,346	$ 159,760	$ 148,252	$ 136,221	$ 119,976	$ 128,418	$ 131,199	$ 630,437	$ 515,814	$ 452,589
Gross profit	32,312	23,507	24,794	22,043	17,366	14,588	16,114	18,407	102,656	66,475	52,751
Income (loss) before income taxes	8,878	3,476	3,371	1,015	(9,204)	(15,653)	(4,523)	(3,908)	16,740	(33,288)	(29,960)
Net income (loss)	$ 5,190	$ 2,057	$ 1,950	$ 561	$ (5,980)	$ (9,114)	$ (2,976)	$ (2,716)	$ 9,758	$ (20,786)	$ (20,018)
Basic	$ 0.36	$ 0.14	$ 0.13	$ 0.04	$ (0.42)	$ (0.63)	$ (0.21)	$ (0.19)	$ 0.67	$ (1.45)	$ (1.40)
Diluted	$ 0.35	$ 0.14	$ 0.13	$ 0.04	$ (0.42)	$ (0.63)	$ (0.21)	$ (0.19)	$ 0.66	$ (1.45)	$ (1.40)