Restructuring and Excess Facilities - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended				36 Months Ended
	Aug. 31, 2018 USD ($)	Jan. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) Employees	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Employees		Dec. 31, 2018 USD ($)	Aug. 01, 2018 USD ($)	Jan. 04, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Gain From TVN Pension Curtailment			$ 0	$ 0	$ 1,955
Restructuring Reserve, Current			3,335	4,443			$ 3,335
Restructuring Reserve, Noncurrent			2,000	3,600			2,000
Restructuring charges			3,056
Payments for Restructuring			6,675
Restructuring Reserve			5,335	8,043			5,335
Restructuring and Related Cost			2,918	5,307	14,602	[1]
Adjustments to restructuring provisions			719
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			317	330
Payments of Voluntary Plan Benefit Obligation			13
Harmonic 2018 Restructuring Plan [Member] | Severance and benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			2,124
Payments for Restructuring			2,052
Restructuring Reserve			$ 0				0
Restructuring and Related Cost, Number of Positions Eliminated | Employees			59
Adjustments to restructuring provisions			$ (116)
Harmonic 2018 Restructuring Plan [Member] | Excess Facilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			932
Payments for Restructuring			203
Restructuring Reserve			1,066				1,066
Adjustments to restructuring provisions			5
Harmonic 2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2,500
Harmonic 2017 Restructuring Plan [Member] | Severance and benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges				2,100
Payments for Restructuring			193
Restructuring Reserve			0	193			0
Harmonic 2017 Restructuring Plan [Member] | Excess Facilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Noncurrent			200				200
Restructuring charges				400
Payments for Restructuring			146
Restructuring Reserve			317	296			317
Adjustments to restructuring provisions			167
Harmonic 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost					20,000
Harmonic 2016 Restructuring Plan [Member] | Excess Facilities [Member]
Restructuring Cost and Reserve [Line Items]
Payments for Restructuring			1,015
Restructuring Reserve			1,543	2,426			1,543
Restructuring and Related Cost					2,200
Adjustments to restructuring provisions			132
Harmonic 2016 Restructuring Plan [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost					$ 17,800
Restructuring and Related Cost, Number of Positions Eliminated | Employees					118
Harmonic 2016 Restructuring Plan [Member] | TVN Voluntary Departure Plan [Member]
Restructuring Cost and Reserve [Line Items]
Payments for Restructuring			3,066
Restructuring Reserve			2,409	5,128			2,409
Adjustments to restructuring provisions			531
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			500	1,800	$ 13,100
Payments of Voluntary Plan Benefit Obligation							13,800
TVN [Member]
Restructuring Cost and Reserve [Line Items]
Gain From TVN Pension Curtailment					2,000
TVN [Member] | Cost of revenue [Member]
Restructuring Cost and Reserve [Line Items]
Gain From TVN Pension Curtailment					600
TVN [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Gain From TVN Pension Curtailment					$ 1,400
TVN [Member] | TVN Voluntary Departure Plan [Member]
Restructuring Cost and Reserve [Line Items]
Postemployment Benefits Liability			2,400	5,100			2,400
TVN [Member] | Harmonic 2016 Restructuring Plan [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Number of Positions Eliminated | Employees					83
San Jose CA Excess Facility [Member] | Harmonic 2018 Restructuring Plan [Member] | Excess Facilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 900
Restructuring Reserve			1,100				1,100
San Jose CA Excess Facility [Member] | Harmonic 2016 Restructuring Plan [Member] | Excess Facilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 1,400
Restructuring Reserve			$ 1,500				$ 1,500
Adjustments to restructuring provisions				$ 1,200
Other Liabilities, Fair Value Disclosure								$ 1,200	$ 2,500
Deferred Rent Credit								$ 300	$ 1,100

[1] The restructuring and related charges for the fiscal year ended December 31, 2016 is net of $0.6 million and $1.4 million, in Cost of revenue and Operating expenses - Restructuring and related charges, respectively, of gain from TVN pension curtailment. See “Harmonic 2016 Restructuring Plan” below for additional information.