v3.19.2
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 31, 2019
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol ROKU  
Entity Registrant Name Roku, Inc.  
Entity Current Reporting Status Yes  
Entity Central Index Key 0001428439  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity File Number 001-38211  
Entity Tax Identification Number 262087865  
Entity Address, Address Line One 150 Winchester Circle  
Entity Address, City or Town Los Gatos  
Entity Address, State or Province California  
Entity Address, Postal Zip Code 95032  
City Area Code 408  
Local Phone Number 556-9040  
Class A Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   85,421,696
Class B Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   30,812,380