Quarterly Financial Data - Summary of Quarterly Financial Data (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 Information Disclosure [Abstract]
Net Sales	$ 48,962	$ 47,108	$ 47,265	$ 45,351	$ 43,483	$ 41,915	$ 47,239	$ 40,075	$ 188,686	$ 172,712	$ 158,836
Gross profit	30,874	30,631	30,743	28,796	27,541	27,417	29,548	24,542	121,044	109,048	98,411
Net Earnings	$ 9,150	$ 10,159	$ 10,249	$ 8,474	$ 8,573	$ 8,594	$ 9,626	$ 6,578	$ 38,032	$ 33,371	$ 26,831
Basic earnings per common share	$ 0.22	$ 0.25	$ 0.25	$ 0.21	$ 0.21	$ 0.21	$ 0.23	$ 0.16	$ 0.92	$ 0.81	$ 0.66
Diluted earnings per common share	$ 0.22	$ 0.24	$ 0.24	$ 0.20	$ 0.21	$ 0.21	$ 0.23	$ 0.16	$ 0.91	$ 0.80	$ 0.65
Cash dividends per common share	$ 0.19	$ 0.19		$ 0.38	$ 0.19	$ 0.19	$ 0.19	$ 0.19	$ 0.76	$ 0.76	$ 0.76