Discontinued Operations - Operating Results of the Disposal Group (Details) - Grass Valley - Discontinued Operations, Held-for-sale [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 56,812	$ 89,178	$ 107,861	$ 176,213
Cost of sales	(33,989)	(53,227)	(69,191)	(102,390)
Gross profit	22,823	35,951	38,670	73,823
Selling, general and administrative expenses	(19,342)	(20,030)	(36,861)	(44,861)
Research and development expenses	(5,974)	(10,259)	(14,473)	(21,166)
Amortization of intangibles	0	(3,299)	0	(8,477)
Asset impairment of discontinued operations	(89,810)	0	(113,007)	0
Interest expense, net	(214)	(207)	(420)	(413)
Non-operating pension cost	(111)	(55)	(196)	(111)
Income (loss) before taxes	$ (92,628)	$ 2,101	$ (126,287)	$ (1,205)

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