Selected Quarterly Financial Data (Unaudited) (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
Selected Quarterly Financial Data (Unaudited)
Net sales	$ 130,732	$ 162,366	$ 177,812	$ 132,536	$ 119,606	$ 146,447	$ 165,614	$ 123,820	$ 603,446	$ 555,487	$ 526,544
Cost of sales	75,822	86,919	94,313	75,588	71,979	80,750	88,828	69,793	332,642	311,349	341,645
Gross profit	54,910	75,447	83,499	56,948	47,627	65,697	76,786	54,027	270,804	244,138	184,899
Research and development and other engineering	6,143	6,804	6,945	5,994	4,954	5,715	5,700	4,742	25,886	21,110	18,756
Selling	18,041	18,633	19,819	17,075	15,865	15,946	16,610	14,872	73,568	63,293	58,790
General and administrative	23,570	25,174	25,454	21,621	22,331	20,001	20,524	16,933	95,820	79,788	75,063
Impairment of goodwill	1,282				6,292				1,282	6,292
Loss (gain) on sale of assets	190	(46)	73	(25)	43	(5,217)	15	388	191	(4,769)	794
Income (Loss) from Operations	5,684	24,882	31,208	12,283	(1,858)	29,252	33,937	17,092	74,057	78,424	31,496
Income (loss) in equity method investment		4,471	(69)	(14)	(106)	(153)	(131)	(144)	4,389	(535)	(194)
Interest income, net	82	79	108	72		110	26	12
Income (loss) from continuing operations before income taxes	5,766	29,432	31,247	12,341	(1,964)	29,209	33,832	16,960	78,786	78,037	31,477
Provision for income taxes from continuing operations	818	10,052	11,754	5,263	2,535	10,801	12,773	7,130	27,886	33,239	17,356
Income from continuing operations, net of tax	4,948	19,380	19,493	7,078	(4,499)	18,408	21,059	9,830	50,900	44,798	14,121
Loss from discontinued operations, net of tax						(1,226)	(14,356)	(631)		(16,212)	(1,904)
Net income	$ 4,948	$ 19,380	$ 19,493	$ 7,078	$ (4,499)	$ 17,182	$ 6,703	$ 9,199	$ 50,900	$ 28,586	$ 12,217
Basic
Continuing operations (in dollars per share)	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ (0.09)	$ 0.37	$ 0.43	$ 0.20	$ 1.04	$ 0.91	$ 0.29
Discontinued operations (in dollars per share)						$ (0.02)	$ (0.29)	$ (0.01)		$ (0.33)	$ (0.04)
Net income (in dollars per share)	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ (0.09)	$ 0.35	$ 0.14	$ 0.19	$ 1.04	$ 0.58	$ 0.25
Diluted
Continuing operations (in dollars per share)	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ (0.09)	$ 0.37	$ 0.42	$ 0.20	$ 1.04	$ 0.90	$ 0.29
Discontinued operations (in dollars per share)						$ (0.02)	$ (0.29)	$ (0.01)		$ (0.33)	$ (0.04)
Net income (in dollars per share)	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ (0.09)	$ 0.35	$ 0.14	$ 0.19	$ 1.04	$ 0.58	$ 0.25
Cash dividends declared per common share (in dollars per share)	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.50	$ 0.40	$ 0.40