Unaudited: Quarterly Results of Operations, Common Stock Price and Dividends (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) shareholder $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) shareholder $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2016 USD ($) shareholder $ / shares	Dec. 31, 2015 USD ($) shareholder $ / shares	Dec. 31, 2014 USD ($) $ / shares
Net sales | $	$ 93,098	$ 96,273	$ 103,820	$ 100,570	$ 95,770	$ 99,388	$ 98,896	$ 83,644	$ 393,761	$ 377,698	$ 364,768
Gross margin | $	33,522	38,647	39,396	39,011	34,457	36,101	35,143	30,075	150,576	135,776	131,142
Net earnings | $	$ 6,113	$ 8,792	$ 9,400	$ 7,990	$ 5,483	$ 8,327	$ 7,901	$ 4,227	$ 32,295	$ 25,938	$ 29,678
Earnings per share:
Basic (in dollars per share)	$ 0.21	$ 0.30	$ 0.33	$ 0.28	$ 0.19	$ 0.29	$ 0.27	$ 0.15
Diluted (in dollars per share)	0.21	0.30	0.32	0.28	0.19	0.29	0.27	0.15
Dividends declared (in dollars per share)	0.115	0.115	0.1	0.1	0.1	0.1	0.095	0.095	$ 0.43	$ 0.39	$ 0.37
Stock price (in dollars per share)	$ 36.95	33.51	36.52	33.26	$ 29.30	29.03	31.75	29.97	$ 36.95	$ 29.30
Number of shareholders | shareholder	922				948				922	948
High
Earnings per share:
Stock price (in dollars per share)	$ 39.15	37.80	39.36	34.74	$ 31.00	32.21	32.94	30.68	$ 39.15	$ 31.00
Low
Earnings per share:
Stock price (in dollars per share)	$ 29.30	$ 31.90	$ 31.72	$ 26.40	$ 27.64	$ 25.82	$ 29.33	$ 27.36	$ 29.30	$ 27.64