Unaudited: Quarterly Results of Operations, Common Stock Price and Dividends (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012 shareholder	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011 shareholder	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 shareholder	Dec. 31, 2011 shareholder	Dec. 31, 2010
Net sales	$ 74,323	$ 87,130	$ 81,974	$ 76,233	$ 60,710	$ 69,698	$ 75,148	$ 57,359	$ 319,660	$ 262,915	$ 276,634
Gross Profit	28,851	34,330	30,201	28,864	19,383	22,780	27,220	20,437	122,246	89,820	102,824
Net earnings	$ 5,484	$ 8,857	$ 7,442	$ 6,249	$ 1,187	$ 6,880	$ 7,834	$ 3,260	$ 28,032	$ 19,161	$ 28,662
Earnings Per Share, Basic (in dollars per share)	$ 0.39	$ 0.63	$ 0.52	$ 0.42	$ 0.08	$ 0.46	$ 0.52	$ 0.22
Earnings Per Share, Diluted (in dollars per share)	$ 0.39	$ 0.62	$ 0.52	$ 0.42	$ 0.08	$ 0.46	$ 0.52	$ 0.22
Common Stock, Dividends, Per Share, Cash Paid (in dollars per share)	$ 0.17	$ 0.17	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.14	$ 0.14
Stock price (in dollars per share)					$ 29.43	$ 28.93	$ 36.99	$ 41.21		$ 29.43
Number of Shareholders	981				952				981	952
Common Stock
Stock price (in dollars per share)	$ 47.41	$ 36.39	$ 37.55	$ 33.99					$ 47.41
Common Stock | Maximum
Stock price (in dollars per share)	$ 48.60	$ 39.85	$ 39.73	$ 35.05	$ 35.41	$ 40.83	$ 41.61	$ 45.47	$ 48.60	$ 35.41
Common Stock | Minimum
Stock price (in dollars per share)	$ 36.25	$ 32.29	$ 32.61	$ 29.30	$ 26.86	$ 28.66	$ 33.98	$ 36.44	$ 36.25	$ 26.86