Commitments and contingencies.

No definition available.

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

- Definition

Indemnification asset released for payment of portion of liabilities assumed.

+ References

No definition available.

+ Details

Name:	roku_IndemnificationAssetReleasedForPaymentOfPortionOfLiabilitiesAssumed
Namespace Prefix:	roku_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Indemnification liability.

+ References

No definition available.

+ Details

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

- Definition

Indemnification liability released for Payment of portion of liabilities assumed.

+ References

No definition available.

+ Details

Name:	roku_IndemnificationLiabilityReleasedForPaymentOfPortionOfLiabilitiesAssumed
Namespace Prefix:	roku_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Letters of credit expiration year.

+ References

No definition available.

+ Details

Name:	roku_LettersOfCreditExpirationYear
Namespace Prefix:	roku_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of indemnification assets (amounts to be reimbursed if and when certain assumed liabilities are paid) recognized at the acquisition date of a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472

+ Details

Name:	us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

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

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AccruedLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentLiabilitiesMember
Namespace Prefix:
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Balance Type:
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- Details

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Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Commitments And Contingencies [Line Items]
Indemnification asset released for payment of portion of liabilities assumed	$ 66.1
Indemnification liability released for payment Of portion of liabilities assumed	66.1
Letters of credit outstanding	30.8	$ 30.8		$ 30.9
Letters of credit expiration year		2030
Manufacturing
Commitments And Contingencies [Line Items]
Purchase commitments for inventory and license	260.5	$ 260.5
Licensed Content
Commitments And Contingencies [Line Items]
Indemnification asset	15.3	15.3	$ 81.4
Indemnification liability	15.3	15.3	$ 81.4
Licensed Content \| Accrued Liabilities
Commitments And Contingencies [Line Items]
Purchase commitments for inventory and license	25.2	25.2		6.2
Licensed Content \| Other Long-Term Liabilities
Commitments And Contingencies [Line Items]
Purchase commitments for inventory and license	4.2	4.2		$ 1.4
Content Publishers
Commitments And Contingencies [Line Items]
Purchase commitments for inventory and license	$ 176.6	$ 176.6