Discontinued Operations - Operating Results of the Disposal Group (Details) - Grass Valley - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 2,000
Asset impairment of discontinued operations		$ (113,000)	$ (521,400)
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues		109,195	360,496	$ 419,666
Cost of sales		(70,199)	(208,173)	(241,164)
Gross profit		38,996	152,323	178,502
Selling, general and administrative expenses		(39,947)	(93,796)	(114,567)
Research and development expenses		(15,083)	(37,172)	(49,033)
Amortization of intangibles		0	(12,782)	(23,689)
Asset impairment of discontinued operations		(113,007)	(521,441)	0
Interest expense, net		(432)	(819)	(720)
Non-operating pension cost		(169)	(221)	(243)
Loss before taxes		$ (129,642)	$ (513,908)	$ (9,750)