Consolidated Statements of Earnings - Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 28, 2015	Jun. 30, 2016	Jun. 28, 2015
Income Statement [Abstract]
Net sales	$ 98,693	$ 100,071	$ 195,398	$ 198,382
Cost of goods sold	64,236	66,698	127,472	132,873
Gross Margin	34,457	33,373	67,926	65,509
Selling, general and administrative expenses	15,764	15,224	30,411	30,935
Research and development expenses	5,967	5,487	12,130	10,686
Restructuring and impairment charges	206	2,118	206	2,856
Operating earnings	24,097	10,542	36,530	21,033
Other (expense) income:
Interest expense	(1,009)	(653)	(1,829)	(1,241)
Interest income	331	853	879	1,641
Gain (Loss) on Disposition of Assets	(11,577)	2	(11,351)	(1)
Other (expense) income	(1,240)	117	(1,436)	(1,570)
Total other (expense) income	(1,918)	317	(2,386)	(1,170)
Earnings before income taxes	22,179	10,859	34,144	19,863
Income tax expense (benefit)	7,692	(8,221)	11,794	(5,504)
Net earnings	$ 14,487	$ 19,080	$ 22,350	$ 25,367
Earnings per share:
Basic (in dollars per share)	$ 0.00	$ 0.01	$ 0.01	$ 0.01
Diluted (in dollars per share)	$ 0.00	$ 0.01	$ 0.01	$ 0.01
Basic weighted - average common shares outstanding (in shares):	32,759	33,080	32,695	33,243
Effect of dilutive securities (in shares)	466	471	485	497
Diluted weighted - average common shares outstanding (in shares)	33,225	33,551	33,180	33,740
Cash dividends declared per share (in dollars per share)	$ 0.0004	$ 0.0004	$ 0.0008	$ 0.0008