Restructuring and Related Charges Schedule of Restructuring Cost by Types (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 28, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 6,365	$ 8,043
Charges for current period	3,056
Adjustments to restructuring provisions	532
Reclassification of deferred rent	332
Cash payments	(5,517)
Foreign exchange effect	(81)
Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Charges for current period		2,500
Facility Closing [Member] \| Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1,770	2,426
Adjustments to restructuring provisions	99
Cash payments	(755)
Facility Closing [Member] \| Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	187	296
Charges for current period		400
Cash payments	(109)
Facility Closing [Member] \| Harmonic 2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1,214
Charges for current period	932
Adjustments to restructuring provisions	1
Reclassification of deferred rent	332
Cash payments	(51)
TVN Voluntary Departure Plan [Member] \| Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	3,188	5,128
Adjustments to restructuring provisions	504
Cash payments	(2,363)
Foreign exchange effect	(81)
Employee Severance [Member] \| Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	193
Charges for current period		$ 2,100
Cash payments	(193)
Employee Severance [Member] \| Harmonic 2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	6
Charges for current period	2,124
Adjustments to restructuring provisions	(72)
Cash payments	$ (2,046)

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Includes, but is not limited to, one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, and termination benefits associated with an ongoing benefit arrangement. Excludes expenses associated with special or contractual termination benefits, a discontinued operation or an asset retirement obligation.

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Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

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Amount of expense (reversal of expense) which increases (decreases) the restructuring reserve from an adjustment to a previously accrued restructuring liability.

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Amount of increase (decrease) in the restructuring reserve related to foreign currency translation (gain) loss and other increases (decreases).

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