Consolidated Quarterly Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quartely financial data [Abstract]
Net Sales	$ 193,158	$ 186,990	$ 201,259	$ 172,591	$ 182,789	$ 168,637	$ 166,137	$ 150,106	$ 753,998	$ 667,667	$ 595,875
Gross Profit	83,529	80,253	83,468	71,931	77,162	71,862	71,543	63,760	319,181	284,326	246,108
Net Earnings (Loss)	$ 11,264	$ 9,728	$ 5,855	$ 5,866	$ 17,012	$ 7,526	$ 6,175	$ 4,091	$ 32,713	$ 34,803	$ (26,241)
Basic Earnings (Loss) per Share (in dollars per share)	$ 0.60	$ 0.52	$ 0.31	$ 0.31	$ 0.91	$ 0.40	$ 0.33	$ 0.22	$ 1.74	$ 1.85	$ (1.42)
Diluted Earnings (Loss) per Share (in dollars per share)	$ 0.59	$ 0.50	$ 0.30	$ 0.30	$ 0.89	$ 0.39	$ 0.32	$ 0.21	$ 1.69	$ 1.80	$ (1.42)
Cash Dividends Declared per Common Share (in dollars share)	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.14	$ 0.14	$ 0.14	$ 0.68	$ 0.59	$ 0.53