Subsequent Events - (Details) - Subsequent Event $ in Millions	Feb. 11, 2023 USD ($) ft²
Sub Lease Agreement
Subsequent Event [Line Items]
Area of real estate property \| ft²	179,496
Operating lease term	7 years
Sub Lease Agreement \| Minimum
Subsequent Event [Line Items]
Lessee, operating lease, annual base rent amount	$ 12.0
Sub Lease Agreement \| Maximum
Subsequent Event [Line Items]
Lessee, operating lease, annual base rent amount	$ 15.0
Sub Lessor Agreement
Subsequent Event [Line Items]
Area of real estate property \| ft²	78,911
Lessor term of contract	4 years
Sub Lessor Agreement \| Minimum
Subsequent Event [Line Items]
Lessor, operating lease, expected annual income	$ 4.0
Sub Lessor Agreement \| Maximum
Subsequent Event [Line Items]
Lessor, operating lease, expected annual income	$ 6.0

Lessee, Operating Lease, Annual Base Rent Amount

No definition available.

Name:	rblx_LesseeOperatingLeaseAnnualBaseRentAmount
Namespace Prefix:	rblx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Lessor, Operating Lease, Expected Annual Income

+ References

No definition available.

+ Details

Name:	rblx_LessorOperatingLeaseExpectedAnnualIncome
Namespace Prefix:	rblx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of lessor's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=124258985&loc=SL77919359-209981

+ Details

Name:	us-gaap_LessorOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_LeaseContractualTermAxis=rblx_SubLesseeAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
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_LeaseContractualTermAxis=rblx_SubLessorAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: