v3.10.0.1
Document And Entity Information - shares
9 Months Ended
Sep. 30, 2018
Nov. 02, 2018
Document And Entity Information [Abstract]    
Entity Registrant Name Xenon Pharmaceuticals Inc.  
Document Type 10-Q  
Trading Symbol XENE  
Current Fiscal Year End Date --12-31  
Amendment Flag false  
Entity Central Index Key 0001582313  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Document Period End Date Sep. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Entity Common Stock, Shares Outstanding   25,240,348