Quarterly Financial Information (Unaudited) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Quarterly financial results
Net sales	$ 128,250	$ 141,886	$ 134,859	$ 135,264	$ 128,487	$ 138,847	$ 137,792	$ 136,350	$ 540,259	$ 541,476	$ 545,394
Gross profit	69,525	77,288	72,980	71,168	71,588	75,756	73,761	69,606	290,961	290,711	296,897
Net income	$ 5,633	$ 8,591	$ 5,877	$ 3,842	$ 5,189	$ 6,941	$ 4,979	$ 2,263	$ 23,943	$ 19,372	$ 22,988
Net income per share—Basic	$ 0.42	$ 0.65	$ 0.44	$ 0.29	$ 0.39	$ 0.53	$ 0.38	$ 0.17	$ 1.80	$ 1.48	$ 1.79
Net income per share—Diluted	$ 0.42	$ 0.64	$ 0.44	$ 0.29	$ 0.39	$ 0.52	$ 0.38	$ 0.17	$ 1.78	$ 1.46	$ 1.75