Entity Central Index Key Document And Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Document Type Document Type Trading Symbol Trading Symbol Current Fiscal Year End Date Current Fiscal Year End Date Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Amendment Flag Amendment Flag Entity Central Index Key Entity Filer Category Entity Filer Category Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Statement Of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Marketable securities Marketable Securities Current Accounts receivable Accounts Receivable Net Current Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Total current assets Assets Current Prepaid expenses, long term Prepaid Expense Noncurrent Property, plant and equipment, net Property Plant And Equipment Net Total assets Assets Liabilities and shareholders’ equity Liabilities And Stockholders Equity [Abstract] Current liabilities: Liabilities Current [Abstract] Accounts payable and accrued expenses (note 6) Accounts Payable And Accrued Liabilities Current Total liabilities Liabilities Shareholders’ equity: Stockholders Equity [Abstract] Common shares, without par value; unlimited shares authorized; issued and outstanding: 17,996,680 (December 31, 2016 - 17,930,590) (note 7a) Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock Accumulated deficit Retained Earnings Accumulated Deficit Accumulated other comprehensive loss Accumulated Other Comprehensive Income Loss Net Of Tax Shareholders' equity Stockholders Equity Total liabilities and shareholders’ equity Liabilities And Stockholders Equity Commitments and contingencies (note 9) Commitments And Contingencies Common shares, without par value Common Stock No Par Value Common shares, shares authorized Common Stock Shares Authorized Unlimited Common shares, Issued Common Stock Shares Issued Common shares, Outstanding Common Stock Shares Outstanding Income Statement [Abstract] Revenue: Revenues [Abstract] Collaboration revenue (note 8) License And Services Revenue Royalties Royalty Revenue Revenues Revenues Operating expenses: Operating Expenses [Abstract] Research and development Research And Development Expense General and administrative General And Administrative Expense Total operating expenses Operating Expenses Loss from operations Operating Income Loss Other income: Other Income And Expenses [Abstract] Interest income Investment Income Interest Foreign exchange gain Foreign Currency Transaction Gain Loss Before Tax Net loss and comprehensive loss Net Income Loss Net loss per common share (note 4): Earnings Per Share [Abstract] Basic Earnings Per Share Basic Diluted Earnings Per Share Diluted Weighted-average common shares outstanding (note 4): Earnings Per Share Basic And Diluted Other Disclosures [Abstract] Basic Weighted Average Number Of Shares Outstanding Basic Diluted Weighted Average Number Of Diluted Shares Outstanding Amount of increase (decrease) to additional paid in capital (APIC) resulting from reclassification of equity classified stock options to liability classified stock options. Statement Of Stockholders Equity [Abstract] Statement [Table] Statement [Table] Accumulated Other Comprehensive Loss [Member] Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Shares [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid In Capital [Member] Accumulated Deficit [Member] Retained Earnings [Member] Accumulated Other Comprehensive Loss [Member] Accumulated Other Comprehensive Income [Member] Statement [Line Items] Statement [Line Items] Balance Balance (in Shares) Shares Outstanding Net loss Issuance of common shares, net of issuance costs Stock Issued During Period Value New Issues Issuance of common shares, net of issuance costs (in Shares) Stock Issued During Period Shares New Issues Stock option compensation expense Adjustments To Additional Paid In Capital Share Based Compensation Stock Options Requisite Service Period Recognition Issued pursuant to exercise of stock options Stock Issued During Period Value Stock Options Exercised Issued pursuant to exercise of stock options (in Shares) Stock Issued During Period Shares Stock Options Exercised Fair value adjustment upon reclassification of stock options Adjustments To Additional Paid In Capital Fair Value Adjustment Upon Reclassification Of Stock Options Balance Balance (in Shares) The aggregate grant-date fair value of options exercised via net exercise (cashless) during the reporting period as calculated by applying the disclosed option pricing methodology. Items not involving cash. Statement Of Cash Flows [Abstract] Operating activities: Net Cash Provided By Used In Operating Activities Continuing Operations [Abstract] Net loss Items not involving cash: Items Not Involving Cash [Abstract] Depreciation and amortization Depreciation And Amortization Stock-based compensation Share Based Compensation Unrealized foreign exchange gain Foreign Currency Transaction Gain Loss Unrealized Changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Accounts receivable Increase Decrease In Accounts Receivable Prepaid expenses, and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Prepaid expenses, long term Increase Decrease In Prepaid Expense Accounts payable and accrued expenses Increase Decrease In Accounts Payable And Accrued Liabilities Deferred revenue Increase Decrease In Deferred Revenue Net cash used in operating activities Net Cash Provided By Used In Operating Activities Continuing Operations Investing activities: Net Cash Provided By Used In Investing Activities Continuing Operations [Abstract] Purchases of property, plant and equipment Payments To Acquire Property Plant And Equipment Proceeds from marketable securities Proceeds From Sale And Maturity Of Marketable Securities Net cash provided by (used in) investing activities Net Cash Provided By Used In Investing Activities Continuing Operations Financing activities: Net Cash Provided By Used In Financing Activities Continuing Operations [Abstract] Issuance of common shares pursuant to exercise of stock options Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Continuing Operations Effect of exchange rate changes on cash and cash equivalents Effect Of Exchange Rate On Cash And Cash Equivalents Continuing Operations Increase (decrease) in cash and cash equivalents Cash And Cash Equivalents Period Increase Decrease Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Supplemental disclosures: Supplemental Cash Flow Information [Abstract] Interest received Interest Income Deposits With Financial Institutions Supplemental disclosures of non-cash transactions: Noncash Investing And Financing Items [Abstract] Fair value of options exercised on a cashless basis Fair Value Of Options Exercised On Cashless Basis Organization Consolidation And Presentation Of Financial Statements [Abstract] Nature of the business Organization Consolidation And Presentation Of Financial Statements Disclosure [Text Block] Accounting Policies [Abstract] Basis of presentation Basis Of Accounting Accounting Changes And Error Corrections [Abstract] Future changes in accounting policies Description Of New Accounting Pronouncements Not Yet Adopted Net income (loss) per common share Earnings Per Share [Text Block] Fair Value Disclosures [Abstract] Fair value of financial instruments Fair Value Disclosures [Text Block] Payables And Accruals [Abstract] Accounts Payable and Accrued Expenses Accounts Payable And Accrued Liabilities Disclosure [Text Block] Stockholders Equity Note [Abstract] Share Capital Stockholders Equity Note Disclosure [Text Block] Collaboration agreements Collaborative Arrangement Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Related Party Transactions [Abstract] Related Parties Related Party Transactions Disclosure [Text Block] Subsequent Events [Abstract] Subsequent Event Subsequent Events [Text Block] Reconciliation of the Numerators and Denominators of Basic and Diluted Net Loss Per Common Share Schedule Of Earnings Per Share Basic And Diluted Table [Text Block] Accounts Payable and Accrued Expenses Schedule Of Accounts Payable And Accrued Liabilities Table [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock Option Activity Schedule Of Share Based Compensation Stock Options Activity Table [Text Block] Fair Value Assumptions for Stock Options Schedule Of Share Based Payment Award Stock Options Valuation Assumptions Table [Text Block] Schedule of Revenues from Collaborations Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions Table [Text Block] Basis of presentation. Basis of presentation. Basis Of Presentation [Table] Basis Of Presentation [Table] Legal Entity Legal Entity [Axis] Entity Entity [Domain] Xenon Pharmaceuticals USA Inc. [Member] Subsidiaries [Member] Basis of Presentation [Line Items] Basis Of Presentation [Line Items] Date of incorporation Entity Incorporation Date Of Incorporation Anti-dilutive shares excluded from the calculation of income per common share Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Net loss used to compute net loss per common share: Earnings Per Share Basic And Diluted [Abstract] Basic Net Income Loss Available To Common Stockholders Basic Adjustment for change in fair value of liability classified stock options Increase Decrease In Fair Value Adjustments On Assets And Liabilities Carried At Fair Value Under Fair Value Option Diluted Net Income Loss Available To Common Stockholders Diluted Weighted average number of common shares: Weighted Average Number Of Shares Outstanding [Abstract] Adjustment for dilutive effect of stock options Incremental Common Shares Attributable To Share Based Payment Arrangements Diluted Net loss per common share - basic Net loss per common share - diluted Carrying value as of the balance sheet date of obligations incurred through that date for consulting and contracted research due within one year. Trade payables Accounts Payable Trade Current Employee compensation, benefits, and related accruals Employee Related Liabilities Current Consulting and contracted research Accrued Consulting And Contracted Research Current Professional fees Accrued Professional Fees Current Other Other Accrued Liabilities Current Total Equity [Abstract] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] Underwritten public offering. Underwritten Public Offering [Member] Underwritten Public Offering [Member] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Issuance of common shares, net of issuance costs (in Shares) Common share price (in Dollars per share) Sale Of Stock Price Per Share Proceeds from net of underwriting discounts and commissions Before offering expenses Proceeds From Issuance Of Common Stock Outstanding, beginning of period Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number Granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross Exercised Forfeited and expired Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures And Expirations In Period Outstanding, end of period Exercisable, end of period Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number Number of common stock issued in exchange for share options (or share units) exercised via net exercise (cashless) method during the current period. Number of share options (or share units) exercised via net exercise (cashless) method during the current period. Number of share options (or share units) exercised for number of common shares for cash during the period. Stock Options exercised for Number of Common Shares for cash Stock Options Exercised For Number Of Common Shares For Cash Common stock issued for cashless exercise Common Stock Issued For Cashless Exercise Cashless exercise of stock options Cashless Exercise Of Stock Options Fair value assumptions for stock options. Fair Value Assumptions For Stock Options [Abstract] Average risk-free interest rate Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Expected volatility Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Average expected term (in years) Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 Expected dividend yield Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate Weighted-average fair value of options granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value Revenue Recognized From Collaborations [Abstract] Revenue Recognized From Collaborations [Abstract] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Counterparty Name Counterparty Name [Axis] Counterparty Name Repurchase Agreement Counterparty Name [Domain] Teva Pharmaceutical Industries Ltd. Teva [Member] Teva Pharmaceutical Industries Ltd [Member] Genentech. Genentech [Member] Genentech [Member] Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others By Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others Type [Domain] Revenue recognized during the period from research funding. Research Funding [Member] Research Funding [Member] Revenue recognized during the period from recognition of upfront payments. Recognition of Upfront Payment [Member] Recognition Of Upfront Payment [Member] Type of Arrangement and Non-arrangement Transactions Type Of Arrangement [Axis] Arrangements and Non-arrangement Transactions Arrangements And Nonarrangement Transactions [Member] Collaborative Arrangement [Member] Collaborative Arrangement [Member] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] Collaboration revenue Contractual obligation paid. Commitments and contingencies. Commitments and contingencies. Commitments And Contingencies [Table] Commitments And Contingencies [Table] Category of Item Purchased Long Term Purchase Commitment By Category Of Item Purchased [Axis] Long-term Purchase Commitment, Category of Item Purchased Long Term Purchase Commitment Category Of Item Purchased [Domain] Medpace clinical development service agreement. Medpace Clinical Development Service Agreement [Member] Medpace Clinical Development Service Agreement [Member] License manufacture and supply agreement. License, Manufacture and Supply Agreement [Member] License Manufacture And Supply Agreement [Member] Commitments and Contingencies [Line Items] Commitments And Contingencies [Line Items] Service agreement, term Unrecorded Unconditional Purchase Obligation Term Committed service obligation Contractual Obligation Contractual obligation paid Contractual Obligation Paid Expenses for services rendered Cost Of Services Current prepaid expenses Prepaid Expense Current Upfront payment required upon signing of license, manufacture and supply agreement. Upfront payment payable License Manufacture And Supply Agreement Upfront Payment Schedule Of Related Party Transactions By Related Party [Table] Schedule Of Related Party Transactions By Related Party [Table] Medpace Clinical Development Service Agreement [Member] Research And Development Arrangement [Member] Related Party Related Party Transactions By Related Party [Axis]