Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.

No definition available.

Name:	dei_AmendmentFlag
Namespace Prefix:	dei_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

PCAOB issued Audit Firm Identifier

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form 10-K
-Number 249
-Section 310

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form 20-F
-Number 249
-Section 220
-Subsection f

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form 40-F
-Number 249
-Section 240
-Subsection f

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Feb. 23, 2026	Jun. 30, 2025
Cover [Abstract]
Document Type	10-K
Entity Registrant Name	XENON PHARMACEUTICALS INC.
Current Fiscal Year End Date	--12-31
Entity Public Float				$ 2,404.9
Entity Common Stock, Shares Outstanding			83,190,316
Amendment Flag	false
Trading Symbol	XENE
Entity Central Index Key	0001582313
Document Annual Report	true
Document Transition Report	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Dec. 31, 2025
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Shares, without par value
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
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
City Area Code	604
Local Phone Number	484-3300
Entity File Number	001-36687
Entity Address, Postal Zip Code	V5G 4W8
Entity Incorporation, State or Country Code	Z4
Entity Address, Country	CA
ICFR Auditor Attestation Flag	true
Auditor Name	PricewaterhouseCoopers LLP	KPMG LLP
Auditor Firm ID	238	85
Auditor Location	Boston, Massachusetts	Vancouver, Canada
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the 2026 Annual Meeting of Shareholders, which will be filed with the Securities and Exchange Commission subsequent to the date hereof, are incorporated by reference into Part III of this Report. Such Proxy Statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the Registrant’s fiscal year ended December 31, 2025.
Auditor Opinion [Text Block]	Opinions on the Financial Statements and Internal Control over Financial Reporting We have audited the accompanying consolidated balance sheet of Xenon Pharmaceuticals Inc. and its subsidiary (the “Company”) as of December 31, 2025, and the related consolidated statements of operations and comprehensive loss, of shareholders’ equity and of cash flows for the year then ended, including the related notes (collectively referred to as the “consolidated financial statements”). We also have audited the Company's internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control - Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission (COSO). In our opinion, the consolidated financial statements referred to above present fairly, in all material respects, the financial position of the Company as of December 31, 2025, and the results of its operations and its cash flows for the year then ended in conformity with accounting principles generally accepted in the United States of America. Also in our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control - Integrated Framework (2013) issued by the COSO. Opinion on the Consolidated Financial Statements We have audited the accompanying consolidated balance sheet of Xenon Pharmaceuticals Inc. (the Company) as of December 31, 2024, the related consolidated statements of operations and comprehensive loss, shareholders' equity, and cash flows for each of the years in the two-year period ended December 31, 2024, and the related notes (collectively, the consolidated financial statements). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2024, and the results of operations and its cash flows for each of the years in the two-year period ended December 31, 2024, in conformity with U.S. generally accepted accounting principles.