Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization	$ 2.7	$ 1.5

Depreciation and amortization of property plant and equipment.

No definition available.

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