v3.19.3
Document And Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 01, 2019
Cover [Abstract]    
Entity Registrant Name Xenon Pharmaceuticals Inc.  
Document Type 10-Q  
Current Fiscal Year End Date --12-31  
Entity Common Stock, Shares Outstanding   25,868,956
Amendment Flag false  
Entity Central Index Key 0001582313  
Entity Filer Category Accelerated Filer  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Small Business true  
Entity Shell Company false  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity File Number 001-36687  
Entity Tax Identification Number 98-0661854  
Entity Address, Address Line One 200-3650 Gilmore Way  
Entity Address, City or Town Burnaby  
Entity Address, State or Province BC  
Entity Address, Country CA  
Entity Address, Postal Zip Code V5G 4W8  
City Area Code 604  
Local Phone Number 484-3300  
Title of 12(b) Security Common Shares, without par value  
Trading Symbol XENE  
Security Exchange Name NASDAQ  
Entity Incorporation, State or Country Code Z4  
Document Quarterly Report true  
Document Transition Report false