Selected Quarterly Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Selected Quarterly Information (Unaudited) [Abstract]
Net sales	$ 36,949	$ 55,201	$ 56,233	$ 43,281	$ 32,805	$ 46,368	$ 50,696	$ 43,101	$ 191,664	$ 172,970	$ 128,533
Gross profit	13,349	22,963	25,060	20,658	12,780	20,556	21,684	19,093	82,030	74,113	47,356
Total income (loss) from operations	6,194	15,601	16,472	12,598	6,049	13,511	13,048	11,797	50,865	44,405	21,108
Other income (expense), net	326	(14)	351	334	94	25	(44)	139	997	214	(206)
Net income	$ 4,266	$ 10,736	$ 11,431	$ 8,685	$ 3,589	$ 9,207	$ 8,702	$ 8,213	$ 35,118	$ 29,711	$ 14,082
Basic earnings per share	$ 0.33	$ 0.84	$ 0.90	$ 0.68	$ 0.28	$ 0.74	$ 0.71	$ 0.67	$ 2.76	$ 2.39	$ 1.17
Diluted earnings per share	$ 0.33	$ 0.83	$ 0.89	$ 0.68	$ 0.28	$ 0.72	$ 0.69	$ 0.65	$ 2.74	$ 2.36	$ 1.14