v3.20.1

Revenue - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Revenue From Contract With Customer [Abstract]
Number of reportable segment | segment	2
Contract with customer assets increase (decrease)	$ 1.2
Increase (decrease) in deferred revenue	2.0
Deferred revenue recognized	20.5	$ 30.7
Estimated contracted revenue	$ 208.7
Revenue, remaining performance obligation, expected timing of satisfaction, Description	Revenue allocated to remaining or unsatisfied performance obligations represents estimated revenue that has not yet been recognized which includes unearned revenue and amounts that will be invoiced and recognized as revenue in future periods. Estimated contracted revenue was $208.7 million as of March 31, 2020 of which we expect to recognize approximately 57% over the next 12 months and the remainder thereafter.
Revenue remaining performance obligation percentage of revenue expected to be recognized	57.00%

X

- Definition

Revenue remaining performance obligation percentage of revenue expected to be recognized.

+ References

No definition available.

+ Details

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Namespace Prefix:	roku_
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Balance Type:	na
Period Type:	duration

X

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045

+ Details

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

X

- Definition

Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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

X

- Definition

Amount of increase (decrease) in deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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Balance Type:	debit
Period Type:	duration

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
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X

- References

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X

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

X

- Definition

Description of when remaining performance obligation is expected to be recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045

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