Restructuring and Related Charges - Additional Information (Detail) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
		Jan. 31, 2016 USD ($)	Mar. 30, 2018 USD ($) Employees	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Employees	Jan. 04, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			$ 7,200		$ 8,000
Restructuring Reserve, Current			4,300		4,400
Restructuring Reserve, Noncurrent			2,900		3,600
Adjustments to restructuring provisions			1,086	$ 1,279
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			6,523		7,554
Restructuring Reserve, Current	[1]		3,756
Restructuring Reserve, Noncurrent	[1]		2,767
Restructuring and Related Cost, Incurred Cost						$ 20,000
Payments for Restructuring			1,131
Adjustments to restructuring provisions			(7)
Facility Closing [Member] | Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Noncurrent			200
Restructuring and Related Cost, Incurred Cost					400
Facility Closing [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve			2,209		2,426
Restructuring Reserve, Current	[1]		892
Restructuring Reserve, Noncurrent	[1]		1,317
Restructuring and Related Cost, Incurred Cost						2,200
Payments for Restructuring			251
Adjustments to restructuring provisions			34
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			400
Restructuring and Related Cost, Incurred Cost			$ 1,800
Number of positions eliminated | Employees			53
Payments for Restructuring			$ 1,400
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			4,314		5,128
Restructuring Reserve, Current	[1]		2,864
Restructuring Reserve, Noncurrent	[1]		1,450
Payments for Restructuring			880
Adjustments to restructuring provisions			(41)
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			4,300		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]
Charges for 2016 Harmonic Restructuring Plan				$ 1,100
Postemployment Benefits Liability			$ 4,300
San Jose CA Excess Facility [Member] | Facility Closing [Member] | Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Charges for 2016 Harmonic Restructuring Plan		$ 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 under “Accrued and other current liabilities” and “Other non-current liabilities”, respectively, on the Company’s Condensed Consolidated Balance Sheets.