Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 31, 2019
Document And Entity Information [Abstract]    
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 GWPH  
Entity Registrant Name GW PHARMACEUTICALS PLC  
Entity Central Index Key 0001351288  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity File Number 001-35892  
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  
Entity Address, City or Town Histon  
Entity Address, State or Province Cambridge  
Entity Address, Postal Zip Code CB24 9BZ  
Entity Address, Country United Kingdom  
Entity Common Stock, Shares Outstanding   370,628,720