Entity Central Index Key Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Ex Transition Period Entity Ex Transition Period Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding The amount expected to be received within one year or the normal operating cycle, if longer, as part of a refundable tax incentive program for research and development activities. 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 Available For Sale Securities Debt Securities Current Tax incentive receivable Tax Incentive Receivable Current Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Total current assets Assets Current Property and equipment, net Property Plant And Equipment Net Other assets Other Assets Noncurrent Total assets Assets Liabilities and Stockholders' Equity Liabilities And Stockholders Equity [Abstract] Current liabilities: Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued expenses Accrued Liabilities Current Notes payable, current Notes Payable Current Total current liabilities Liabilities Current Notes payable, long-term Long Term Notes Payable Total liabilities Liabilities Commitments and contingencies (Note 7) Commitments And Contingencies Stockholders' equity: Stockholders Equity [Abstract] Preferred stock; $0.001 par value per share; 5,000,000 shares authorized as of September 30, 2018 and December 31, 2017; no shares issued and outstanding as of September 30, 2018 and December 31, 2017 Preferred Stock Value Common stock, $0.001 par value per share; 115,000,000 shares authorized as of September 30, 2018 and December 31, 2017; 36,865,817 and 27,489,457 shares issued and outstanding as of September 30, 2018 and December 31, 2017, respectively 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 Total stockholders' equity Stockholders Equity Total liabilities and stockholders' equity Liabilities And Stockholders Equity Preferred stock, par value per share Preferred Stock Par Or Stated Value Per Share Preferred stock, shares authorized Preferred Stock Shares Authorized Preferred stock, shares issued Preferred Stock Shares Issued Preferred stock, shares outstanding Preferred Stock Shares Outstanding Common stock, par value per share Common Stock Par Or Stated Value Per Share Common stock, shares authorized Common Stock Shares Authorized Common stock, shares issued Common Stock Shares Issued Common stock, shares outstanding Common Stock Shares Outstanding Income Statement [Abstract] Revenue 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 (expense): Other Income And Expenses [Abstract] Interest income Investment Income Net Interest expense Interest Expense Foreign currency transaction (losses) gains, net Foreign Currency Transaction Gain Loss Before Tax Total other income (expense), net Nonoperating Income Expense Net loss Net Income Loss Net loss per share, basic and diluted Earnings Per Share Basic And Diluted Weighted average common shares outstanding, basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Comprehensive loss: Comprehensive Income Net Of Tax [Abstract] Net loss Other comprehensive loss: Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent [Abstract] Unrealized (loss) gain on marketable securities Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent Total other comprehensive (loss) income Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Total comprehensive loss Comprehensive Income Net Of Tax The cash outflow associated with the premium paid on marketable securities. The increase (decrease) during the reporting period in tax incentive receivable, which represents the amount due from tax authorities. Statement Of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided By Used In Operating Activities [Abstract] Net loss Profit Loss Adjustments to reconcile net loss to net cash used in operating activities Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Stock-based compensation expense Share Based Compensation Non-cash interest expense Paid In Kind Interest Depreciation expense Depreciation Unrealized foreign currency transaction losses (gains) Foreign Currency Transaction Gain Loss Unrealized Premium on marketable securities, net Premium On Marketable Securities Amortization of (discount) premium on marketable securities Investment Income Net Amortization Of Discount And Premium Changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Prepaid expenses and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Tax incentive receivable Increase Decrease In Tax Incentives Receivable Accounts payable Increase Decrease In Accounts Payable Accrued expenses Increase Decrease In Accrued Liabilities Net cash used in operating activities Net Cash Provided By Used In Operating Activities Cash flows from investing activities: Net Cash Provided By Used In Investing Activities [Abstract] Proceeds from sales and maturities of marketable securities Proceeds From Sale And Maturity Of Available For Sale Securities Purchases of marketable securities Payments To Acquire Available For Sale Securities Debt Purchases of property and equipment Payments To Acquire Property Plant And Equipment Net cash (used in) provided by investing activities Net Cash Provided By Used In Investing Activities Cash flows from financing activities: Net Cash Provided By Used In Financing Activities [Abstract] Proceeds from public offering, net of issuance costs Proceeds From Issuance Initial Public Offering Repayments of notes payable Repayments Of Notes Payable Proceeds from exercise of common stock options and employee stock purchase plan Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options Net cash provided by (used in) financing activities Net Cash Provided By Used In Financing Activities Net increase (decrease) in cash and cash equivalents Cash And Cash Equivalents Period Increase Decrease Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Supplemental disclosure of non-cash investing and financing activities: Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract] Property and equipment included in accounts payable Capital Expenditures Incurred But Not Yet Paid Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for interest Interest Paid Net Accounting Policies [Abstract] Nature of the Business and Basis of Presentation Business Description And Basis Of Presentation [Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements and Marketable Securities Fair Value Disclosures [Text Block] Payables And Accruals [Abstract] Accrued Expenses Accounts Payable And Accrued Liabilities Disclosure [Text Block] Debt Disclosure [Abstract] Notes Payable Debt Disclosure [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock-Based Awards Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Compensation And Retirement Disclosure [Abstract] Retirement Plan Pension And Other Postretirement Benefits Disclosure [Text Block] Research And Development [Abstract] Australia Research and Development Tax Incentive Research Development And Computer Software Disclosure [Text Block] Use of Estimates Use Of Estimates Marketable securities Marketable Securities Policy Net Loss Per Share Earnings Per Share Policy [Text Block] Recently Issued and Adopted Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block] Summary of Common Stock Equivalents Outstanding Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Summary of Cash Equivalents and Marketable Securities Fair Value Assets Measured On Recurring And Nonrecurring Basis Table [Text Block] Summary of Marketable Securities Available For Sale Securities [Text Block] Schedule of Accrued Expenses Schedule Of Accrued Liabilities Table [Text Block] Schedule of Estimated Future Principal Payments Schedule Of Maturities Of Long Term Debt Table [Text Block] Summary of Stock-Based Compensation Expense Related to Stock Options, Restricted Common Stock and ESPP Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Schedule of Future Minimum Lease Payments for Operating Leases Schedule Of Future Minimum Rental Payments For Operating Leases Table [Text Block] Organization Consolidation And Presentation Of Financial Statements [Abstract] Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items] Organization Consolidation And Presentation Of Financial Statements Disclosure [Table] Organization Consolidation And Presentation Of Financial Statements Disclosure [Table] Organization Consolidation And Presentation Of Financial Statements Disclosure [Table] Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] Public Offering [Member] I P O [Member] Long-term Debt, Type Longterm Debt Type [Axis] Long-term Debt, Type Longterm Debt Type [Domain] Term Loan [Member] Term Loan [Member] Term Loan [Member] Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items] Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items] Entity incorporation date Entity Incorporation Date Of Incorporation Net proceeds from sale of securities. Accumulated deficit Net proceeds from sale of securities Net Proceeds From Sale Of Securities Issuance of common stock Stock Issued During Period Shares New Issues Share price per share Shares Issued Price Per Share Net proceeds from public offering, after underwriting discount, commission and offering expenses Aggregate principal balance Debt Instrument Face Amount Loan agreement minimum liquidity required Restricted Cash And Investments Total cash, cash equivalents and marketable securities Cash Cash Equivalents And Short Term Investments Earnings Per Share [Abstract] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Antidilutive Securities Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis] Antidilutive Securities, Name Antidilutive Securities Name [Domain] Options to Purchase Common Stock [Member] Employee Stock Option [Member] Unvested Restricted Common Stock [Member] Restricted Stock [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Total potentially dilutive shares Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Hierarchy and NAV Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Quoted Prices in Active Markets, (Level 1) [Member] Fair Value Inputs Level1 [Member] Significant Other Observable Inputs (Level 2) [Member] Fair Value Inputs Level2 [Member] Significant Unobservable Inputs (Level 2) [Member] Fair Value Inputs Level3 [Member] Investment Type Investment Type [Axis] Investments Investment Type Categorization [Member] Money Market Funds [Member] Money Market Funds [Member] Commercial Paper [Member] Commercial Paper [Member] Corporate Bonds [Member] Corporate Bond Securities [Member] U.S. Government Securities [Member] U S Government Corporations And Agencies Securities [Member] Certificates of Deposit [Member] Certificates Of Deposit [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Cash equivalents Cash And Cash Equivalents Fair Value Disclosure Total cash equivalents and marketable securities Assets Fair Value Disclosure Debt Securities Available For Sale [Table] Debt Securities Available For Sale [Table] Corporate Bonds (Due within 1 Year) [Member] Commercial Paper (Due within 1 Year) [Member] U.S. Government Securities (Due within 1 Year) [Member] Certificates of Deposit (Due Within 1 Year) [Member] Schedule of Available-for-sale Securities [Line Items] Schedule Of Available For Sale Securities [Line Items] Amortized Cost Available For Sale Debt Securities Amortized Cost Basis Gross Unrealized Gains Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax Gross Unrealized Losses Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax Fair Value Carrying value as of the balance sheet date of obligations incurred through that date and payable for expenses related to research and development. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Accrued research and development expenses Accrued Research And Development Expense Current Accrued payroll and related expenses Employee Related Liabilities Current Accrued professional fees Accrued Professional Fees Current Accrued other Other Accrued Liabilities Current Total accrued expense Debt Instrument [Table] Debt Instrument [Table] Range Range [Axis] Range Range [Member] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Credit Facility Credit Facility [Axis] Credit Facility Credit Facility [Domain] Two thousand and fourteen credit facility. 2014 Credit Facility [Member] Two Thousand And Fourteen Credit Facility [Member] Secured Debt [Member] Secured Debt [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Maximum borrowings under term loan Proceeds from issuance of notes payable Proceeds From Notes Payable The fee, as a percentage of the term loan, due as a final payment. Debt facility description Debt Instrument Description Debt maturity date Debt Instrument Maturity Date Debt facility interest rate description Debt Instrument Description Of Variable Rate Basis Debt facility interest rate Debt Instrument Basis Spread On Variable Rate1