Quarterly Financial Information (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Quarterly Financial Information Disclosure [Line Items]
Sales	$ 165,605	$ 174,738	$ 178,064	$ 158,429	$ 149,404	$ 156,078	$ 167,009	$ 155,911
Gross profit	36,351	43,156	44,091	34,912	32,043	37,070	39,161	35,238	158,510	143,512	135,085
Net income	$ 6,024	$ 11,333	$ 11,787	$ 6,950	$ 4,199	$ 8,575	$ 9,344	$ 6,785	$ 36,094	$ 28,903	$ 32,687
Per common share - diluted
Diluted (in dollars per share)	$ 0.49	$ 0.93	$ 0.97	$ 0.57	$ 0.35	$ 0.71	$ 0.77	$ 0.56	$ 2.96	$ 2.40	$ 2.73
Average shares
Diluted (in shares)	12,262	12,229	12,200	12,158	12,090	12,056	12,058	12,027	12,212,000	12,058,000	11,966,000
Dividends per share (in dollars per share)	$ 0.07	$ 0.07	$ 0.07	$ 0.07	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.24	$ 0.24	$ 0.24
High
Market price of common stock
Share Price (in dollars per share)	$ 61.27	$ 49.45	$ 44.13	$ 40.64	$ 34.63	$ 34.00	$ 34.23	$ 30.93	$ 61.27	$ 34.63
Low
Market price of common stock
Share Price (in dollars per share)	$ 45.51	$ 40.48	$ 37.39	$ 33.12	$ 29.66	$ 27.07	$ 29.40	$ 25.51	$ 45.51	$ 29.66