Selected Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Selected Quarterly Financial Data (Unaudited)
Net sales	$ 144,686	$ 172,113	$ 181,703	$ 158,734	$ 130,732	$ 162,366	$ 177,812	$ 132,536	$ 657,236	$ 603,446	$ 555,487
Cost of sales	89,482	96,390	98,557	89,329	75,822	86,919	94,313	75,588	373,759	332,642	311,349
Gross profit	55,204	75,723	83,146	69,405	54,910	75,447	83,499	56,948	283,477	270,804	244,138
Research and development and other engineering	8,763	8,916	9,043	9,198	6,143	6,804	6,945	5,994	35,919	25,886	21,110
Selling	21,109	20,941	19,881	20,432	18,041	18,633	19,819	17,075	82,364	73,568	63,293
General and administrative	23,799	23,843	27,087	26,244	23,570	25,174	25,454	21,621	100,973	95,820	79,788
Impairment of goodwill	2,346				1,282				2,346	1,282	6,292
Loss (gain) on sale of assets	124	33	(13)	23	190	(46)	73	(25)	166	191	(4,769)
Income from continuing operations	(937)	21,990	27,148	13,508	5,684	24,882	31,208	12,283	61,709	74,057	78,424
Income (loss) in equity method investment						4,471	(69)	(14)		4,389	(535)
Interest income, net	35	55	58	65	82	79	108	72
Income from continuing operations before taxes	(902)	22,045	27,206	13,573	5,766	29,432	31,247	12,341	61,921	78,786	78,037
Provision for (benefit from) income taxes	(6,785)	9,069	11,347	6,372	818	10,052	11,754	5,263	20,003	27,886	33,239
Net income	$ 5,883	$ 12,976	$ 15,859	$ 7,201	$ 4,948	$ 19,380	$ 19,493	$ 7,078	$ 41,918	$ 50,900	$ 28,586
Earnings per common share:
Basic (in dollars per share)	$ 0.12	$ 0.27	$ 0.33	$ 0.15	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ 0.87	$ 1.04	$ 0.58
Diluted (in dollars per share)	$ 0.12	$ 0.27	$ 0.33	$ 0.15	$ 0.10	$ 0.40	$ 0.39	$ 0.14	$ 0.87	$ 1.04	$ 0.58
Cash dividends declared per common share (in dollars per share)	$ 0.25	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.625	$ 0.50	$ 0.40