| Document and Entity Information | Nov. 08, 2019 |
| Cover [Abstract] | |
| Security Exchange Name | NASDAQ |
| Amendment Flag | true |
| Entity Central Index Key | 0001428439 |
| Document Type | 8-K/A |
| Document Period End Date | Nov. 8, 2019 |
| Entity Registrant Name | ROKU, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38211 |
| Entity Tax Identification Number | 26-2087865 |
| Entity Address, Address Line One | 150 Winchester Circle |
| Entity Address, City or Town | Los Gatos |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 95032 |
| City Area Code | 408 |
| Local Phone Number | 556-9040 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Stock, $0.0001 par value |
| Trading Symbol | ROKU |
| Entity Emerging Growth Company | false |
| Amendment Description | On November 14, 2019, Roku, Inc. filed a Current Report on Form 8-K (the “Original Form 8-K”), reporting, among other items, that on November 8, 2019, through our wholly-owned subsidiary Delaware Acquisition Company, Inc., we consummated the previously announced acquisition of Dataxu, Inc., a Delaware corporation, pursuant to the Agreement and Plan of Merger dated October 22, 2019, as amended on November 8, 2019 (the “Merger”). This Amendment No. 1 to Current Report on Form 8-K amends the Original Form 8-K to provide (i) the historical financial statements of Dataxu, Inc. and (ii) the unaudited pro forma condensed combined financial information required by Items 9.01(a) and 9.01(b) of Current Report on Form 8-K, respectively. Such financial information was excluded from the Original Form 8-K in reliance on the instructions to such items. This Amendment No. 1 to Current Report on Form 8-K further amends Items 2.01 and 3.02 to lower the number of shares of Class A common stock issued to the former Dataxu securityholders from 571,516 shares to 571,459 shares due to the elimination of fractional shares. |
