Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 segment	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Segment Information
Number of reportable segments			3
Segment Information
Net sales	$ 195,596	$ 181,703	$ 350,130	$ 340,437
Sales to Other Segments	6,439	6,034	11,616	11,264
Income (loss) from operations	29,678	27,148	38,691	40,656
Total Assets	896,985	878,905	896,985	878,905	890,322
Cash and short-term investments	165,275	162,719	165,275	162,719	175,553	213,817
North America
Segment Information
Net sales	159,757	144,532	287,493	272,500
Sales to Other Segments	1,170	1,442	1,931	2,814
Income (loss) from operations	29,665	26,583	44,924	44,456
Total Assets	603,981	557,502	603,981	557,502	583,501
Europe
Segment Information
Net sales	32,099	34,120	56,016	62,356
Sales to Other Segments	394	19	674	153
Income (loss) from operations	2,241	2,088	(1,939)	(284)
Total Assets	188,563	204,864	188,563	204,864	194,000
Asia/Pacific
Segment Information
Net sales	3,502	2,735	6,147	5,107
Sales to Other Segments	4,875	4,573	9,011	8,297
Income (loss) from operations	(46)	(163)	(1,229)	(817)
Total Assets	32,408	31,734	32,408	31,734	30,455
Administrative and all other
Segment Information
Net sales	238	316	474	474
Income (loss) from operations	(2,182)	(1,360)	(3,065)	(2,699)
Total Assets	72,033	84,805	72,033	84,805	82,366
Cash and short-term investments	$ 86,800	$ 82,600	$ 86,800	$ 82,600	$ 91,900