| Document and Entity Information - USD ($) | 12 Months Ended | ||
| Dec. 31, 2020 | Apr. 23, 2021 | Jun. 30, 2020 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | true | ||
| Amendment Description | EXPLANATORY NOTE GW Pharmaceuticals plc (the “Company” or “we” or “us” or “GW”) is filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to amend our Annual Report on Form 10-K for the year ended December 31, 2020 (the “Original Form 10-K”), originally filed with the Securities and Exchange Commission (the “SEC”) on February 26, 2021 (the “Original Form 10-K”), to include the information required by Items 10 through 14 of Part III of our Form 10-K. This information was previously omitted from our Form 10-K in reliance on General Instruction G(3) to Form 10-K, which permits the information in the above referenced items to be incorporated in our Form 10-K by reference from our definitive proxy statement if such statement is filed no later than 120 days after our fiscal year-end. We are filing this Amendment to include Part III information in our Form 10-K because a definitive proxy statement containing such information will not be filed by April 30, 2021. Except as otherwise expressly noted herein, this Amendment does not modify or update in any way the financial position, results of operations, cash flows, or other disclosures in, or exhibits to, the Original Form 10-K, nor does it reflect events occurring after the filing of the Original Form 10-K. Accordingly, this Amendment should be read in conjunction with the Original Form 10-K. In addition, as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), new certifications by the Company’s principal executive officer and principal financial officer are filed herewith as exhibits to this Amendment pursuant to Rule 13a-14(a) or 15d-14(a) of the Exchange Act. As no financial statements have been included in this Amendment and it does not contain or amend any disclosure with respect to Items 307 or 308 of Regulation S-K, paragraphs 3, 4, and 5 of the certifications have been omitted. The Company is not including certifications pursuant to Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. 1350) as no financial statements are being filed with this Amendment. | ||
| Document Period End Date | Dec. 31, 2020 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Entity Registrant Name | GW PHARMACEUTICALS PLC | ||
| Entity Central Index Key | 0001351288 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Well-known Seasoned Issuer | Yes | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity Filer Category | Large Accelerated Filer | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | false | ||
| Entity Shell Company | false | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Entity File Number | 001-35892 | ||
| Entity Incorporation, State or Country Code | X0 | ||
| Entity Tax Identification Number | 00-0000000 | ||
| City Area Code | +44 | ||
| Local Phone Number | 1223 266800 | ||
| Entity Address, Address Line One | Sovereign House | ||
| Entity Address, Address Line Two | Vision Park | ||
| Entity Address, Address Line Three | Chivers Way, Histon | ||
| Entity Address, City or Town | Cambridge | ||
| Entity Address, Postal Zip Code | CB24 9BZ | ||
| Entity Address, Country | GB | ||
| Entity Common Stock, Shares Outstanding | 378,535,952 | ||
| Entity Public Float | $ 3,735,551,435 | ||
| ICFR Auditor Attestation Flag | true | ||
| Title of 12(b) Security | American Depositary Shares, each representing 12 Ordinary Shares, par value £0.001 per share | ||
| Trading Symbol | GWPH | ||
| Security Exchange Name | NASDAQ | ||
| Documents Incorporated by Reference | DOCUMENTS INCORPORATED BY REFERENCE None. |
