Condensed Consolidated Statements of Operations- Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2020	Sep. 27, 2019	Oct. 02, 2020	Sep. 27, 2019
Income Statement [Abstract]
Sales	$ 235,942	$ 303,587	$ 804,483	$ 932,457
Cost of sales	178,009	210,201	591,985	653,477
Gross profit	57,933	93,386	212,498	278,980
Operating expenses:
Selling, general and administrative expenses (Note 10)	3,609	32,935	73,969	101,034
Research, development and engineering costs	11,892	11,729	37,879	34,720
Other operating expenses	2,674	2,241	7,631	8,239
Total operating expenses	18,175	46,905	119,479	143,993
Operating income	39,758	46,481	93,019	134,987
Interest expense, net	9,368	12,337	29,002	39,779
(Gain) loss on equity investments, net	(2,234)	(986)	(3,954)	666
Other (income) loss, net	1,224	(369)	(233)	(921)
Income from continuing operations before taxes	31,400	35,499	68,204	95,463
Provision for income taxes	1,058	4,913	6,373	15,289
Income from continuing operations	30,342	30,586	61,831	80,174
Discontinued operations:
Income from discontinued operations before taxes	0	0	0	5,316
Provision for income taxes	0	0	0	178
Income from discontinued operations	0	0	0	5,138
Net income	$ 30,342	$ 30,586	$ 61,831	$ 85,312
Basic earnings per share:
Income from continuing operations (in dollars per share)	$ 0.92	$ 0.94	$ 1.88	$ 2.46
Income from discontinued operations (in dollars per share)	0	0	0	0.16
Basic earnings per share (in dollars per share)	0.92	0.94	1.88	2.62
Diluted earnings per share:
Income from continuing operations (in dollars per share)	0.92	0.92	1.87	2.43
Income from discontinued operations (in dollars per share)	0	0	0	0.16
Diluted earnings per share (in dollars per share)	$ 0.92	$ 0.92	$ 1.87	$ 2.58
Weighted average shares outstanding:
Basic (in shares)	32,859	32,660	32,833	32,606
Diluted (in shares)	33,076	33,068	33,107	33,019