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, 2013 shareholder	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012 shareholder	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 shareholder	Dec. 31, 2012 shareholder	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011
Net sales	$ 81,010	$ 92,963	$ 88,341	$ 71,808	$ 74,323	$ 87,130	$ 81,974	$ 76,233	$ 334,122	$ 319,660	$ 262,915
Gross margin	29,003	33,103	29,846	25,037	28,851	34,330	30,201	28,864	116,989	122,246	89,820
Net earnings	$ 6,380	$ 9,049	$ 6,281	$ 2,907	$ 5,484	$ 8,857	$ 7,442	$ 6,249	$ 24,617	$ 28,032	$ 19,161
Earnings Per Share, Basic (in dollars per share)	$ 0.44	$ 0.63	$ 0.44	$ 0.21	$ 0.39	$ 0.63	$ 0.52	$ 0.42
Earnings Per Share, Diluted (in dollars per share)	$ 0.44	$ 0.63	$ 0.44	$ 0.20	$ 0.39	$ 0.62	$ 0.52	$ 0.42
Dividends declared (in dollars per share)	$ 0.18	$ 0.18	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.16	$ 0.16
Stock price (in dollars per share)					$ 47.41					$ 47.41		$ 36.39	$ 37.55	$ 33.99
Number of shareholders	969				981				969	981
Common Stock
Stock price (in dollars per share)	$ 54.50	$ 46.50	$ 44.55	$ 53.52					$ 54.50
Common Stock | High
Stock price (in dollars per share)	$ 56.36	$ 49.96	$ 54.28	$ 54.20	$ 48.60				$ 56.36	$ 48.60		$ 39.85	$ 39.73	$ 35.05
Common Stock | Low
Stock price (in dollars per share)	$ 44.80	$ 43.96	$ 41.88	$ 46.82	$ 36.25				$ 44.80	$ 36.25		$ 32.29	$ 32.61	$ 29.30