Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 24, 2021	Jun. 26, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	000-25826
Entity Registrant Name	HARMONIC INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0201147
Entity Address, Address Line One	2590 Orchard Parkway
Entity Address, City or Town	San Jose
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95131
City Area Code	408
Local Phone Number	542-2500
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	HLIT
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 239,854,000
Entity Common Stock, Shares Outstanding		100,847,272
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000851310
Current Fiscal Year End Date	--12-31
Documents Incorporated by Reference	Portions of the Proxy Statement for the Registrant’s 2021 Annual Meeting of Stockholders (which will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year ended December 31, 2020) are incorporated by reference in Part III of this Annual Report on Form 10-K.