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		12 Months Ended
	Apr. 04, 2021	Mar. 29, 2020	Dec. 31, 2020
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment revenues	$ 536,381	$ 463,526
Total Segment EBITDA	79,469	60,239
Amortization of Intangible Assets	(9,947)	(16,185)
Depreciation expense	(11,560)	(10,282)
Severance, restructuring, and acquisition integration costs	(5,171)	(3,619)
Amortization of software development intangible assets	(689)	(330)
Purchase accounting effects related to acquisitions		(20)
Operating income	51,448	29,708
Interest Income (Expense), Net	(15,511)	(13,324)
Non-operating pension benefit	(684)	(699)
Consolidated income from continuing operations before taxes	36,621	17,083
OTN Systems N.V.
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Amortization of Intangible Assets	(1,600)
Inventory adjustment	800
Reportable Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment revenues	536,381	463,526
Total Segment EBITDA	79,469	60,239
Amortization of Intangible Assets	(9,947)	(16,185)
Depreciation expense	(11,560)	(10,282)
Severance, restructuring, and acquisition integration costs	(5,171)	(3,619)
Amortization of software development intangible assets	(689)	(330)
Purchase accounting effects related to acquisitions	(621)	(20)
Impairment of assets held-for-use	3,600
Impairment of assets to be held for sale	3,400
Collection of receivables, previously written off	1,400
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]
Inventory adjustment	800
Intersegment Eliminations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment Elimination	$ (33)	$ (95)