v3.20.1

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2020 USD ($)	Mar. 31, 2020 USD ($) FinancialInstitution Customer	Dec. 31, 2019 USD ($) FinancialInstitution Customer	Mar. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 1,539	$ 1,854	$ 26,350
Content licensing expenses		14,500	$ 1,700
Accounting Standards Update 2016-13
Summary Of Significant Accounting Policies [Line Items]
Cumulative-effect adjustment to accumulated deficit	$ 1,100	$ 1,066
Customer Concentration Risk | Net Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Number of customers accounted for 10% or more | Customer		0	0
Customer 1
Summary Of Significant Accounting Policies [Line Items]
Number of financial institutions which manage cash balances | FinancialInstitution		1	1
Customer 1 | Cash and Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Percentage of cash and cash equivalents balances		57.00%	65.00%
Customer 2
Summary Of Significant Accounting Policies [Line Items]
Number of financial institutions which manage cash balances | FinancialInstitution		1	1
Customer 2 | Cash and Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Percentage of cash and cash equivalents balances		43.00%	34.00%

X

- Definition

Content licensing expense.

+ References

No definition available.

+ Details

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

X

- Definition

Number of customers.

+ References

No definition available.

+ Details

Name:	roku_NumberOfCustomers
Namespace Prefix:	roku_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of financial institutions.

+ References

No definition available.

+ Details

Name:	roku_NumberOfFinancialInstitutions
Namespace Prefix:	roku_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Summary of significant accounting policies.

+ References

No definition available.

+ Details

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

X

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

+ Details

Name:	us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

X

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_MajorCustomersAxis=roku_CustomerOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_MajorCustomersAxis=roku_CustomerTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: