Reportable Segments - Reconciliation of Total Reportable Segments' Revenues and EBITDA to Consolidated Revenues and Consolidated Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2021	Sep. 27, 2020	Oct. 03, 2021	Sep. 27, 2020
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment revenues	$ 630,835	$ 475,839	$ 1,769,190	$ 1,364,176
Amortization of Intangible Assets	(9,696)	(16,104)	(28,745)	(48,306)
Depreciation expense	(11,300)	(10,500)	(34,200)	(31,100)
Severance, restructuring, and acquisition integration costs	(4,328)	(1,357)	(12,539)	(9,448)
Operating income	71,166	36,127	188,571	82,965
Interest expense, net	(16,251)	(15,607)	(46,640)	(43,188)
Loss on debt extinguishment	(5,715)	0	(5,715)	0
Total non-operating pension benefit	992	680	3,121	2,079
Consolidated income from continuing operations before taxes	50,192	21,200	139,337	41,856
Impairment of assets to be held for sale	2,300
OTN Systems N.V.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Amortization of Intangible Assets	(1,400)		(3,700)
Inventory adjustment	400		2,400
Reportable Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment revenues	631,338	475,839	1,770,542	1,364,176
Adjustments related to acquisitions	(503)	0	(1,352)	0
Total Segment EBITDA	99,738	64,641	271,207	173,560
Amortization of Intangible Assets	(9,696)	(16,104)	(28,745)	(48,306)
Depreciation expense	(11,270)	(10,455)	(34,197)	(31,069)
Severance, restructuring, and acquisition integration costs	(4,328)	(1,357)	(12,539)	(9,448)
Amortization of software development intangible assets	(790)	(529)	(2,086)	(1,245)
Purchase accounting effects related to acquisitions	(2,464)	0	(4,997)	(125)
Impairment of assets to be held for sale	2,300		5,700
Collection of receivables, previously written off	700		2,200
Impairment of assets held-for-use			3,600
Reportable Segment | Opterna International Corp.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Business combination, increase (decrease) in earn-out liability			(5,800)
Reportable Segment | OTN Systems N.V.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Deferred revenue adjustment	500		1,300
Inventory adjustment	400		2,400
Intersegment Eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment Elimination	$ (24)	$ (69)	$ (72)	$ (402)