v3.19.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2019
Apr. 30, 2019
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Trading Symbol ROKU  
Entity Registrant Name Roku, Inc.  
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  
Class A Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   81,981,559
Class B Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   31,437,092