Restructuring and Related Charges - Additional Information (Detail) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
		Jan. 31, 2016 USD ($)	Jun. 29, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 29, 2018 USD ($) Employees	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Employees	Jan. 04, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			$ 6,100		$ 6,100		$ 8,000
Restructuring Reserve, Current			3,500		3,500		4,400
Restructuring Reserve, Noncurrent			2,600		2,600		3,600
Adjustments to restructuring provisions			631	$ 777	1,717	$ 2,056
Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost							2,500
Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			5,835		5,835		7,554
Restructuring Reserve, Current	[1]		3,346		3,346
Restructuring Reserve, Noncurrent	[1]		2,489		2,489
Restructuring and Related Cost, Incurred Cost								$ 20,000
Payments for Restructuring					2,155
Adjustments to restructuring provisions					543
Facility Closing [Member] | Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Noncurrent			200		200
Restructuring and Related Cost, Incurred Cost							400
Facility Closing [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			1,990		1,990		2,426
Restructuring Reserve, Current	[1]		900		900
Restructuring Reserve, Noncurrent	[1]		1,090		1,090
Restructuring and Related Cost, Incurred Cost								2,200
Payments for Restructuring					502
Adjustments to restructuring provisions					66
Employee Severance And Benefit Arrangements [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost								$ 17,800
Number of positions eliminated | Employees								118
Employee Severance [Member] | Harmonic 2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Current			100		100
Restructuring and Related Cost, Incurred Cost					$ 1,800
Number of positions eliminated | Employees					55
Payments for Restructuring					$ 1,700
Employee Severance [Member] | Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost							2,100
TVN Voluntary Departure Plan [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			3,845		3,845		5,128
Restructuring Reserve, Current	[1]		2,446		2,446
Restructuring Reserve, Noncurrent	[1]		1,399		1,399
Payments for Restructuring					1,653
Adjustments to restructuring provisions					477
TVN [Member]
Restructuring Cost and Reserve [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment								$ 2,000
Postemployment Benefits Liability			3,400		3,400		5,100
TVN [Member] | Employee Severance And Benefit Arrangements [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | Employees								83
TVN [Member] | TVN Voluntary Departure Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges					500	$ 1,800
Postemployment Benefits Liability			$ 3,800		$ 3,800
San Jose CA Excess Facility [Member] | Facility Closing [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 1,400
Fair Value of Excess Facility Restructuring									$ 2,500
Deferred Rent Credit									$ 1,100
Adjustments to restructuring provisions							$ 1,200

[1] The current portion and long-term portion of the restructuring liability are reported as components of “Accrued and other current liabilities” and “Other non-current liabilities”, respectively, on the Company’s Condensed Consolidated Balance Sheets.