Number of Patent Infringements.

No definition available.

Name:	hlit_NumberOfPatentInfringements
Namespace Prefix:	hlit_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.25)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LitigationReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount of estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs, which is expected to be paid after one year or beyond the normal operating cycle, if longer.

+ References

+ Details

Name:	us-gaap_LitigationReserveNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_LitigationCaseAxis=hlit_AvidMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=hlit_SettledLitigationPaymentSecondQuarterof2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=hlit_SettledLitigationPaymentThirdQuarterof2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=hlit_MediagridMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=hlit_AvidTechnologyInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=hlit_SpectrumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Legal Proceedings - Additional Information (Detail) $ in Millions		12 Months Ended
	Oct. 24, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 29, 2017 USD ($)	Jun. 29, 2012 Patents	Oct. 31, 2011 Patents
Avid [Member]
Loss Contingencies [Line Items]
Estimated Litigation Liability			$ 6.0
Payments for Legal Settlements	$ 2.5
Settled Litigation Payment Second Quarter of 2019 [Member] \| Avid [Member]
Loss Contingencies [Line Items]
Estimated Litigation Liability, Noncurrent			1.5
Settled Litigation Payment Third Quarter of 2020 [Member] \| Avid [Member]
Loss Contingencies [Line Items]
Estimated Litigation Liability, Noncurrent			$ 2.0
Media grid [Member] \| Avid Technology Inc. [Member]
Loss Contingencies [Line Items]
Infringements of number of patents held \| Patents					2
Spectrum [Member] \| Avid Technology Inc. [Member]
Loss Contingencies [Line Items]
Infringements of number of patents held \| Patents				1
Selling, General and Administrative Expenses [Member] \| Avid [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Expense		$ 6.0