Debt instrument adjusted quick ratio.

No definition available.

Name:	roku_DebtInstrumentAdjustedQuickRatio
Namespace Prefix:	roku_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument amortization description.

+ References

No definition available.

+ Details

Name:	roku_DebtInstrumentAmortizationDescription
Namespace Prefix:	roku_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument amortization percentage.

+ References

No definition available.

+ Details

Name:	roku_DebtInstrumentAmortizationPercentage
Namespace Prefix:	roku_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument basis spread on variable rate applicable margin.

+ References

No definition available.

+ Details

Name:	roku_DebtInstrumentBasisSpreadOnVariableRateApplicableMargin
Namespace Prefix:	roku_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, covenant required minimum current ratio.

+ References

No definition available.

+ Details

Name:	roku_DebtInstrumentCovenantRequiredMinimumCurrentRatio
Namespace Prefix:	roku_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument secured leverage ratio.

+ References

No definition available.

+ Details

Name:	roku_DebtInstrumentSecuredLeverageRatio
Namespace Prefix:	roku_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of debt to consolidated earnings before interest tax depreciation and amortization ratio.

+ References

No definition available.

+ Details

Name:	roku_DescriptionOfDebtToConsolidatedEarningsBeforeInterestTaxDepreciationAndAmortizationRatio
Namespace Prefix:	roku_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Letter of credit maximum borrowing capacity.

+ References

No definition available.

+ Details

Name:	roku_LetterOfCreditMaximumBorrowingCapacity
Namespace Prefix:	roku_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=roku_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=roku_SecondAmendmentToRestatedTwentyFourteenLoanAndSecurityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=roku_MorganStanleySeniorFundingIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=roku_TermLoanAFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentRedemptionPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentRedemptionPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_FederalFundsEffectiveSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=roku_OneMonthLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=roku_AdjustedOneTwoThreeOrSixMonthLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=roku_UncommittedIncrementalFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=roku_SiliconValleyBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=roku_AmendedAndRestatedTwentyFourteenLoanAndSecurityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=roku_ThirdAmendmentToRestatedTwentyFourteenLoanAndSecurityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Additional Information (Details) - USD ($)		1 Months Ended	6 Months Ended
Debt - Additional Information (Details) - USD ($)	Feb. 19, 2019	Jun. 30, 2017	Jun. 30, 2019	May 03, 2019	Dec. 31, 2018	Jul. 18, 2018	Jun. 30, 2018
Debt Instrument [Line Items]
Outstanding debt			$ 0		$ 0
Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 50,000,000.0
Second Amendment To Restated 2014 Loan and Security Agreement
Debt Instrument [Line Items]
Minimum current ratio required under financial covenant		1.25%
Second Amendment To Restated 2014 Loan and Security Agreement \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		2.75%
Second Amendment To Restated 2014 Loan and Security Agreement \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Morgan Stanley Senior Funding, Inc \| Credit Agreement
Debt Instrument [Line Items]
Adjusted quick ratio			1.00%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Term Loan A Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000.0
Debt instrument term, years	4 years
Debt instrument, amortization description	Loans under the Term Loan A Facility will amortize in equal quarterly installments beginning on the last day of the fiscal quarter ending after the date of the initial borrowing under the Term Loan A Facility, in an aggregate annual amount equal to (i) on or prior to December 31, 2021, 1.25% of the drawn principal amount of the Term Loan Facility and (ii) thereafter, 2.50% of the drawn principal amount of the Term Loan Facility, with any remaining balance payable on the maturity date of the Term Loan A Facility.
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Term Loan A Facility \| On or Prior to December 31, 2021
Debt Instrument [Line Items]
Percentage of amortization on drawn principal amount	1.25%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Term Loan A Facility \| Thereafter December 31, 2021
Debt Instrument [Line Items]
Percentage of amortization on drawn principal amount	2.50%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000.0
Debt instrument term, years	4 years
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility \| Term Loan A Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 25,000,000.0
Interest payments description	Loans under the Credit Facility bear interest at a rate equal to, at the Company’s election, (i) an alternate base rate, based upon the highest of (x) the prime rate published by the Wall Street Journal, (y) the federal funds effective date plus ½ of 1% and (z) the one-month LIBOR plus 1%, in each case plus an applicable margin of up to 1% per annum, with step-downs based on its secured leverage ratio or (2) an adjusted one-, two-, three-, or six month LIBOR, at its election, plus an applicable margin of up to 2% per annum, with step-downs based on its secured leverage ratio.
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility \| Term Loan A Facility \| Federal Funds Effective Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility \| Term Loan A Facility \| One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility \| Term Loan A Facility \| Maximum
Debt Instrument [Line Items]
Applicable margin with step-downs based on secured leverage ratio	1.00%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Revolving Credit Facility \| Term Loan A Facility \| Maximum \| Adjusted One-, Two-, Three-, or Six Month LIBOR
Debt Instrument [Line Items]
Applicable margin with step-downs based on secured leverage ratio	2.00%
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Uncommitted Incremental Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000.0
Debt to company's EBITDA, description	1.0x of the Company’s EBITDA for the most recently completed four fiscal quarter period
Morgan Stanley Senior Funding, Inc \| Credit Agreement \| Uncommitted Incremental Facility \| Maximum
Debt Instrument [Line Items]
Secured leverage ratio	1.50%
Silicon Valley Bank \| Restated 2014 LSA
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 5,000,000.0
Silicon Valley Bank \| Restated 2014 LSA \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 30,000,000.0
Silicon Valley Bank \| Third Amendment To Restated 2014 Loan and Security Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 5,000,000.0
Maximum borrowing capacity						$ 30,000,000.0