Accounting Policies [Abstract] Accounting Policies [Abstract] Accounts Payable and Accrued Liabilities Disclosure [Text Block] Accrued Expenses Accounts Payable, Current Accounts payable Accretion of issuance costs related to redeemable convertible preferred stock. Accretion of Issuance Costs Related to Redeemable Convertible Preferred Stock Accretion of issuance costs related to redeemable convertible preferred stock Accrued Liabilities, Current Accrued expenses and other current liabilities Accrued expenses Accrued Liabilities, Current [Abstract] Accrued Liabilities, Current [Abstract] Accrued Rent, Current Short-term deferred rent Accrued research and development expense current. Accrued Research And Development Expense Current Research and development costs Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Less: Accumulated depreciation and amortization Additional Paid in Capital, Common Stock Additional paid-in capital Additional stock issued during period, shares, conversion of convertible securities. Additional Stock Issued During Period, Shares, Conversion of Convertible Securities Additional shares purchase upon exercise of warrant Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net loss to net cash used in operating activities: Allocated Share-based Compensation Expense Total stock based compensation expense Alternative Investment, Measurement Input Expected cash dividend yield Amendment Flag Amendment Flag Amortization of Deferred Charges Amortization of deferred offering costs Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive securities excluded from computation of earnings per share amount Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Arrangements and Non-arrangement Transactions [Domain] Arrangements and Non-arrangement Transactions [Domain] Assets Total assets Assets [Abstract] Assets Assets, Current Total current assets Assets, Current [Abstract] Current assets: Assets, Fair Value Disclosure Assets Fair Value Disclosure Assets, Fair Value Disclosure [Abstract] Assets Fair Value Disclosure Award Type [Axis] Award Type [Axis] Basis of Accounting, Policy [Policy Text Block] Basis of presentation BioMarin Pharmaceutical Inc. BioMarin Pharmaceutical Inc [Member] BioMarin Pharmaceutical Inc [Member] Board. Board Member [Member] Board Member [Member] Capital Expenditures Incurred but Not yet Paid Purchases of property and equipment included in accounts payable and accrued expense Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Net increase (decrease) in cash and cash equivalents Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Supplemental disclosure of non-cash investing and financing activities: Class of Stock [Domain] Class of Stock [Domain] Class of Stock [Line Items] Class of Stock [Line Items] Class of Warrant or Right, Exercise Price of Warrants or Rights Warrant exercise price Class of Warrant or Right [Line Items] Class of Warrant or Right [Line Items] Class of Warrant or Right, Number of Securities Called by Warrants or Rights Warrant to purchase shares Class of Warrant or Right [Table] Class of Warrant or Right [Table] Commitments and Contingencies Commitments and contingencies (Note 13) Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Commitments and contingencies disclosure. Commitments And Contingencies Disclosure [Line Items] Commitments And Contingencies Disclosure [Line Items] Commitments And Contingencies Disclosure [Table] Commitments And Contingencies Disclosure [Table] Commitments And Contingencies Disclosure [Table] Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Common Stock, Capital Shares Reserved for Future Issuance Total shares of authorized common stock reserved for future issuance Common Stock, Par or Stated Value Per Share Common stock, par value Common Stock, Shares Authorized Common stock, authorized Common stock, shares authorized Common Stock, Shares, Issued Common stock, issued Common stock, shares issued Common Stock, Shares, Outstanding Common stock, outstanding Common Stock, Value, Issued Common stock, $0.0001 par value; 150,000,000 and 51,000,000 shares authorized as of September 30, 2018 and December 31, 2017, respectively; 23,942,929 and 2,581,474 shares issued as of September 30, 2018 and December 31, 2017, respectively; 23,758,898 and 2,305,173 shares outstanding as September 30, 2018 and December 31, 2017, respectively Compensation Related Costs, Policy [Policy Text Block] Stock-Based Compensation Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive loss Comprehensive Income, Policy [Policy Text Block] Comprehensive Income (Loss) Computer Equipment [Member] Computer Equipment and Software [Member] Concentration Risk, Credit Risk, Policy [Policy Text Block] Concentrations of Credit Risk Consulting services agreement. Consulting Services Agreement [Member] Consulting Services Agreement [Member] Conversion of Stock, Shares Issued Preferred stock converted into common stock Convertible Preferred Stock, Shares Issued upon Conversion Common Stock Issuable Upon Conversion Counterparty Name [Axis] Counterparty Name [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Debt Instrument Fair Value Carrying Value [Abstract] Debt Instrument Fair Value Carrying Value [Abstract] Debt Instrument Fair Value Carrying Value [Abstract] Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Summary of Prepaid Expenses and Other Current Assets Deferred Rent Credit, Noncurrent Deferred rent, net of current portion Deferred rent expense. Deferred Rent Expense Deferred rent expense Deposits Assets, Current Deposits Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization expense Depreciation, Depletion and Amortization Depreciation and amortization expense Derivative Liability, Fair Value, Gross Liability Fair value of derivative liability Derivative Financial Instruments, Liabilities [Member] Derivative Liabilities [Member] Derivative Liability, Noncurrent Derivative liability Dilution Payment Payable Current Dilution Payment Payable Current Dilution payment Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Stock-Based Compensation Document and entity information. Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Document Fiscal Year Focus Document Fiscal Year Focus Document Period End Date Document Period End Date Document Type Document Type Earnings Per Share [Abstract] Earnings Per Share [Abstract] Earnings Per Share, Basic and Diluted Net loss per share attributable to common stockholders - basic and diluted (Note 12) Earnings Per Share [Text Block] Net Loss per Share Emerging growth company status. Emerging Growth Company Status [Policy Text Block] Emerging Growth Company Status Employee-related Liabilities, Current Compensation and benefit costs Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Unrecognized stock-based compensation expense, period for recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options Unrecognized stock-based compensation expenses Employee Stock Option [Member] Employee Stock Option [Member] Entity Central Index Key Entity Central Index Key Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Emerging Growth Company Entity Emerging Growth Company Entity Ex Transition Period Entity Ex Transition Period Entity Filer Category Entity Filer Category Entity Registrant Name Entity Registrant Name Entity Small Business Entity Small Business Equity [Abstract] Equity [Abstract] Equity Method Investment, Ownership Percentage Issuance of common stock ownership percentage Fabry license agreement. FabryLicenseAgreement [Member] Fabry License Agreement [Member] Fair Value Adjustment of Warrants Change in fair value of preferred stock warrant liability Loss related to change in fair value of warrant Change in fair value of preferred stock warrant liability Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract] Asset Class [Domain] Asset Class [Domain] Asset Class [Axis] Asset Class [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Liability Class [Axis] Liability Class [Axis] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Fair Value Disclosures [Text Block] Fair Value of Financial Assets and Liabilities The fair value input amount of assets and liabilities between levels. Fair Value Input Amount Transfer Between Levels Fair value input transfer between levels Fair Value, Inputs, Level 1 [Member] Level 1 [Member] Fair Value, Inputs, Level 3 [Member] Level 3 [Member] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Summary of Changes in Fair Value Determined by Level 3 Inputs Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value Measurement, Policy [Policy Text Block] Fair Value Measurements Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value, Measurements, Recurring [Member] Fair Value on Recurring Basis [Member] Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 Payment Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Conversion Preferred Warrants To Common Stock Warrants Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Conversion Preferred Warrants To Common Stock Warrants Conversion of preferred stock warrant to common stock warrant Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease) Change in fair value Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Ending balance Beginning balance Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] Fair value of assets and liabilities measured on non recurring basis. Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items] Federal Home Loan Banks [Abstract] Federal Home Loan Banks [Abstract] Gain (Loss) on Derivative Instruments, Net, Pretax Change in fair value of derivative liability Change in fair value of derivative liability Increase in fair value of derivative General and Administrative Expense General and administrative General and Administrative Expense [Member] General and Administrative Expense [Member] GenStem Therapeutics Inc. GenStem Therapeutics Inc [Member] GenStem Therapeutics Inc [Member] Impairment of Long-Lived Assets Held-for-use Impairment loss of property and equipment Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Accrued expenses and other current liabilities Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Other Noncurrent Liabilities Other long-term liability Increase (Decrease) in Other Operating Assets Other assets Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses and other current assets Increase (Decrease) in Restricted Cash Change in restricted cash Initial public offering costs in accrued liabilities. Initial Public Offering Costs in Accrued Liabilities Offering cost Initial Public Offering Policy Text Block. Initial Public Offering [ Policy Text Block] Initial Public Offering Interleukin 12 license agreement. Interleukin12 License Agreement [Member] Interleukin 12 License Agreement [Member] Investment Income, Interest Interest income IPO Issuance costs included in accrued expenses. IPO Issuance Costs Included in Accrued Expenses IPO issuance costs included in accrued expenses IPO [Member] IPO [Member] Issuance of warrants in connection with debt. Issuance Of Warrants In Connection With Debt Issuance of warrants associated with debt facility Lease Expiration Date Lease agreement expiration date Lease termination date Leasehold Improvements [Member] Leasehold Improvements [Member] Lessee, Leases [Policy Text Block] Leases Liabilities Total liabilities Liabilities and Equity Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit) Liabilities and Equity [Abstract] Liabilities, redeemable convertible preferred stock and stockholders' equity (deficit) Liabilities, Current Total current liabilities Liabilities, Current [Abstract] Current liabilities: Financial and Nonfinancial Liabilities, Fair Value Disclosure Liabilities Fair Value Disclosure Liabilities, Fair Value Disclosure [Abstract] Liabilities Fair Value Disclosure License agreement disclosure. License Agreement Disclosure [Text Block] License Agreements License agreement. License Agreement [Line Items] License Agreement [Line Items] License agreement. License Agreement [Member] License Agreement [Member] License Agreements [Abstract] License Agreements [Abstract] License Agreements [Abstract] License Agreement [Table] License Agreement [Table] License Agreement [Table] License Maintenance Fees License Maintenance Fees Annual maintenance fees Line of Credit Facility, Capacity Available for Trade Purchases Available facility Line of Credit Facility, Maximum Borrowing Capacity Maximum issuance of term loans Loan agreement and warrant to purchase preferred stock disclosure. Loan Agreement and Warrant to Purchase Preferred Stock Disclosure [Text Block] Loan Agreement and Warrant to Purchase Preferred Stock Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Floating interest rate per annum Loss on Derivative Instruments, Pretax Initial fair value of the derivative Lund University Rights Holders Agreement. Lund University Rights Holders Agreement [Member] Lund University Rights Holders Agreement [Member] Maximum [Member] Maximum [Member] Measurement Input, Expected Dividend Rate [Member] Expected Dividend Yield [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Milestone payment. Milestone Payment Milestone payments Milestone payments. Milestone Payments Milestone payments Minimum [Member] Minimum [Member] Money Market Funds [Member] Money Market Funds [Member] Nature of organization and operations. Nature Of Organization And Operations [Line Items] Nature Of Organization And Operations [Line Items] Nature Of Organization And Operations [Table] Nature Of Organization And Operations [Table] Nature Of Organization And Operations [Table] Net Cash Provided by (Used in) Financing Activities Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Cash flows from financing activities: Net Cash Provided by (Used in) Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Cash flows from investing activities: Net Cash Provided by (Used in) Operating Activities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Cash flows from operating activities: Net Income (Loss) Attributable to Parent Net loss Net loss Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Reconciliation of net loss to net loss attributable to common stockholders: Net income loss available to common stockholders basic and diluted. Net Income Loss Available To Common Stockholders Basic And Diluted Net loss attributable to common stockholders-basic and diluted Net Income (Loss) per Share Attributable to Common Stockholders [Policy Text Block] Net Income (Loss) per Share Attributable to Common Stockholders [Policy Text Block] Net Income (Loss) per Share Attributable to Common Stockholders New Accounting Pronouncements, Policy [Policy Text Block] Recently Issued Accounting Pronouncements Noninterest Expense Offering Cost Initial public offering expenses Nonoperating Income (Expense) Total other income (expense), net Nonoperating Income (Expense) [Abstract] Other income (expense): Number of shares of common stock outstanding increase percentage. Number Of Shares Of Common Stock Outstanding Increase Percentage Number of shares of common stock outstanding, increase, percentage Office Equipment [Member] Laboratory and Office Equipment [Member] Officers and board members. Officers And Board Members [Member] Officers and Board Members [Member] Operating Expenses Total operating expenses Operating Expenses [Abstract] Operating expenses: Operating Income (Loss) Loss from operations Operating lease annual increase in rental percentage. Operating Lease Annual Increase in Rental Percentage Percentage of annual increase in rent Option fee. Option Fee Option fee Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Nature of the Business and Basis of Presentation Other Accrued Liabilities, Current Other liabilities Other Assets, Current Other current assets Other Assets, Noncurrent Other assets Other Liabilities, Noncurrent Other long-term liability Other Nonoperating Expense Other expense Payables and Accruals [Abstract] Payables and Accruals [Abstract] Payment of dilution liability. Payment of Dilution Liability Payment of dilution liability Payments for (Proceeds from) Tenant Allowance Tenant incentive allowance Payments of Debt Issuance Costs Payments of issuance costs on debt facility Payments to Acquire Property, Plant, and Equipment Purchases of property and equipment Payments upon closing of initial public offering. Payments Upon Closing Of Initial Public Offering Payments upon closing of an initial public offering Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Preferred Stock, Accretion of Redemption Discount Accretion of issuance costs on redeemable convertible preferred stock Preferred Stock, Par or Stated Value Per Share Preferred stock, par value Preferred Stock, Shares Authorized Preferred stock, authorized Preferred Stock, Shares Issued Preferred stock issued Preferred stock, issued Preferred Stock, Value, Issued Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued as of September 30, 2018 Prepaid development costs current. Prepaid Development Costs Current Prepaid development costs Prepaid Expense and Other Assets, Current Prepaid expenses and other current assets Total Prepaid Expense and Other Assets, Current [Abstract] Prepaid Expense and Other Assets, Current [Abstract] Prepaid expenses and other current assets disclosure. Prepaid Expenses And Other Current Assets Disclosure [Text Block] Prepaid Expenses and Other Current Assets Prepaid Rent Prepaid rent Prime Rate [Member] Prime Rate [Member] Proceeds from Issuance Initial Public Offering Net proceeds from IPO, after deducting underwriting discounts and commissions and other offering expenses Proceeds from issuance of common shares upon completion of initial public offering, net of offering costs Proceeds from Issuance of Redeemable Convertible Preferred Stock Proceeds from issuance of redeemable convertible preferred stock Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss Property and equipment held for sale. Property and Equipment Held for Sale Property and equipment held for sale Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment Disclosure [Text Block] Property and Equipment, Net Property, Plant and Equipment, Gross Property plant and equipment, gross Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property, Plant and Equipment, Net Property and equipment, net Property plant and equipment, net Property, Plant and Equipment [Table Text Block] Summary of Property and Equipment, Net Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Provision for maximum cash payment. Provision for Maximum Cash Payment Provision for maximum cash payment Purchases of property and equipment paid for by landlord. Purchases of Property and Equipment Paid for by Landlord Purchases of property and equipment paid for by landlord Range [Axis] Range [Axis] Range [Domain] Range [Domain] Redeemable Convertible Preferred Stock [Member] Redeemable Convertible Preferred Stock [Member] Related Party [Domain] Related Party [Domain] Related Party Transaction, Expenses from Transactions with Related Party Expense related to related party Related Party Transaction [Line Items] Related Party Transaction [Line Items] Related Party Transactions [Abstract] Related Party Transactions [Abstract] Related Party [Axis] Related Party [Axis] Related Party Transactions Disclosure [Text Block] Related Party Transactions Counterparty Name [Domain] Counterparty Name [Domain] Research and Development Expense Research and development Research and development expense related to license agreements Research and Development Expense [Member] Research and Development Expense [Member] Research and Development Expense, Policy [Policy Text Block] Research and Development Costs Restricted cash. Restricted Cash [Member] Restricted Cash [Member] Restricted Stock [Member] Restricted Stock [Member] Retained Earnings (Accumulated Deficit) Accumulated deficit Reverse Stock Split [Policy Text Block] Reverse Stock Split [Policy Text Block] Reverse Stock Split Sale of Stock [Domain] Sale of Stock [Domain] Schedule of Accrued Liabilities [Table Text Block] Summary of Accrued Expenses and Other Current Liabilities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Schedule of Stock-based Compensation Expense Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Summary of Restricted Stock Unit Activity Share-based Compensation, Stock Options, Activity [Table Text Block] Summary of Stock Option Activity Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table Text Block] Summary of Common Stock Reserved for Future Issuance Security Deposit Security deposit in connection with lease Segment Reporting, Policy [Policy Text Block] Segment Information Series A Preferred Stock [Member] Series A Preferred Stock [Member] Series A- Redeemable Convertible Preferred Stock. Series A- Redeemable Convertible Preferred Stock [Member] Series A Redeemable Convertible Preferred Stock [Member] Series B Preferred Stock [Member] Series B Preferred Stock [Member] Series B Redeemable Convertible Preferred Stock. Series B Redeemable Convertible Preferred Stock [Member] Series B Redeemable Convertible Preferred Stock [Member] Series Seed Convertible Preferred Stock. Series Seed Convertible Preferred Stock [Member] Series Seed Redeemable Convertible Preferred Stock [Member] Share-based Compensation Stock-based compensation expense Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Option vesting period Share-based Compensation Arrangement by Share-based Payment Award, Description Employee Stock Purchase Plan, description Share based compensation arrangement by share based payment award equity instruments other than options forfeited and expirations in period. Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited And Expirations In Period Number of shares, Forfeited, cancelled or expired Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Common stock issued for initial consideration for license Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Number of shares, Issued and unvested ending balance Number of shares, Issued and unvested beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Weighted average grant date fair value, Issued and unvested, ending balance Weighted average grant date fair value, Issued and unvested, beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Number of shares, Vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Total fair value of restricted common stock vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Weighted average grant date fair value, Vested Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Expected option life (years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Number of common shares that may increase under the plan Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of common shares that may be issued under the plan Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Common shares available for future grant Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Aggregate intrinsic value, Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Number of options, Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Weighted average exercise price, Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted average remaining contractual term, Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Weighted average exercise price, Cancelled or forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Number of options, Cancelled or forfeited Share based compensation arrangement by share based payment award options granted in period weighted average remaining contractual term. Share Based Compensation Arrangement By Share Based Payment Award Options Granted In Period Weighted Average Remaining Contractual Term Weighted average remaining contractual term, Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Number of options granted Number of options, Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Options Granted, Weighted-average grant-date fair value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Aggregate intrinsic value, Outstanding balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Number of options, Outstanding ending balance Number of options, Outstanding beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Weighted average exercise price, Outstanding ending balance Weighted average exercise price, Outstanding beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted average remaining contractual term, Outstanding balance Share based compensation arrangement by share based payment award options unvested. Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Number of options, Unvested Share based compensation arrangement by share based payment award options unvested aggregate intrinsic value. Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Aggregate Intrinsic Value Aggregate intrinsic value, Unvested Share based compensation arrangement by share based payment award options unvested weighted average exercise price. Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Weighted Average Exercise Price Weighted average exercise price, Unvested Share based compensation arrangement by share based payment award options unvested weighted average remaining contractual term 1. Share Based Compensation Arrangement By Share Based Payment Award Options Unvested Weighted Average Remaining Contractual Term 1 Weighted average remaining contractual term, Unvested Equity Award [Domain] Equity Award [Domain] Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Weighted average exercise price, Exercised Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Weighted average exercise price, Granted Shares Issued, Price Per Share Public offering price Redeemable convertible preferred stock, sales price per share Significant Accounting Policies [Abstract] Significant Accounting Policies [Abstract] Significant Accounting Policies [Abstract] Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Significant of accounting policies. Significant Of Accounting Policies [Line Items] Significant Of Accounting Policies [Line Items] Significant Of Accounting Policies [Table] Significant Of Accounting Policies [Table] Significant Of Accounting Policies [Table] Class of Stock [Axis] Class of Stock [Axis] Statement [Line Items] Statement [Line Items] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Stockholders' Equity Attributable to Parent Total stockholders' equity (deficit) Stockholders' Equity Attributable to Parent [Abstract] Stockholders' equity (deficit): Stockholders' Equity Note Disclosure [Text Block] Common Stock Stockholders' Equity Note, Stock Split, Conversion Ratio Reverse stock split ratio Stockholders' Equity, Policy [Policy Text Block] Warrant to Purchase Preferred Stock Stock Issued During Period, Shares, Conversion of Convertible Securities Shares purchase upon exercise of warrant Stock Issued During Period, Shares, New Issues Common shares issued and sold in initial public offering Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Number of options, Exercised Stock Issued During Period, Value, New Issues Fair value of shares issued Stock purchase agreement. Stock Purchase Agreement [Member] Stock Purchase Agreement [Member] Sub-lease agreement. Sublease Agreement [Member] Sub-lease Agreement [Member] Subsequent Events, Policy [Policy Text Block] Subsequent Event Considerations Sale of Stock [Axis] Sale of Stock [Axis] Temporary Equity, by Class of Stock [Table] Temporary Equity, by Class of Stock [Table] Temporary Equity, Carrying Amount, Attributable to Parent Carrying Value Redeemable convertible preferred stock (Note 8) Temporary Equity Disclosure [Abstract] Temporary Equity Disclosure [Abstract] Temporary Equity [Line Items] Temporary Equity [Line Items] Temporary Equity, Liquidation Preference Liquidation Preference Temporary Equity, Par or Stated Value Per Share Redeemable convertible preferred stock, par value Temporary Equity, Shares Authorized Preferred Shares Authorized Redeemable convertible preferred stock, shares authorized Temporary Equity, Shares Issued Preferred Shares Issued Redeemable convertible preferred stock, shares issued and sold Temporary Equity, Shares Outstanding Preferred Shares Outstanding Temporary equity stock issuance costs. Temporary Equity Stock Issuance Costs Redeemable convertible preferred stock, net of issuance costs Temporary Equity [Table Text Block] Summary of Preferred Stock Temporary equity. Temporary Equity [Text Block] Redeemable Convertible Preferred Stock Text Block [Abstract] Text Block [Abstract] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Trading Symbol Trading Symbol 2018 employee stock purchase plan. Two Thousand Eighteen Employee Stock Purchase Plan [Member] 2018 Employee Stock Purchase Plan [Member] 2018 stock option and incentive plan. Two Thousand Eighteen Stock Option and Incentive Plan [Member] 2018 Stock Option and Incentive Plan [Member] Two thousand fifteen stock option and grant plan. Two Thousand Fifteen Stock Option and Grant Plan [Member] 2015 Stock Option and Grant Plan [Member] Type of Arrangement and Non-arrangement Transactions [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] UHN agreement. UHNAgreement [Member] UHN Agreement [Member] Underwriting discounts and commissions. Underwriting Discounts And Commissions Underwriting discounts and commissions Upfront fees. Upfront Fees Upfront fee Represents the amount of the upfront license fees. Upfront License Fees Upfront license fee Upfront payment paid in cash. Upfront Payment Paid In Cash Upfront cash payment Use of Estimates, Policy [Policy Text Block] Use of Estimates Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Warrant [Member] Warrant [Member] Warrants and Rights Outstanding Warrant to purchase redeemable convertible preferred stock Warrants and Rights Outstanding, Maturity Date Warrant expiration date Warrants to purchase redeemable convertible preferred stock. Warrants to Purchase Redeemable Convertible Preferred Stock [Member] Warrants to Purchase Redeemable Convertible Preferred Stock [Member] Weighted Average Number of Shares Outstanding, Basic and Diluted Weighted-average number of common shares used in computing net loss per share attributable to common stockholders-basic and diluted