Entity Central Index Key Document and entity information. 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 Well-known Seasoned Issuer Entity Well Known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Entity Voluntary Filers Entity Voluntary Filers 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 Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Entity Public Float Entity Public Float Statement Of Financial Position [Abstract] ASSETS Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Restricted cash Restricted Cash And Cash Equivalents At Carrying Value Short-term investments Short Term Investments Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Total current assets Assets Current Long-term investments Long Term Investments 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 and other current liabilities Accrued Liabilities And Other Liabilities Current portion of deferred revenue Contract With Customer Liability Current Total current liabilities Liabilities Current Long-term liabilities: Liabilities Noncurrent [Abstract] Deferred revenue, less current portion Contract With Customer Liability Noncurrent Other long-term liabilities Other Liabilities Noncurrent Total long-term liabilities Liabilities Noncurrent Total liabilities Liabilities Commitments (Note 14) Commitments And Contingencies Stockholders' equity: Stockholders Equity [Abstract] Preferred stock, $0.001 par value, 10,000,000 shares authorized; 0 shares outstanding at December 31, 2018 and December 31, 2017, respectively Preferred Stock Value Common stock, $0.0001 par value, 100,000,000 shares authorized; 24,835,951 and 24,390,033 shares outstanding at December 31, 2018 and December 31, 2017, respectively Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax Accumulated deficit Retained Earnings Accumulated Deficit Total stockholders' equity Stockholders Equity Total liabilities and stockholders' equity Liabilities And Stockholders Equity Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Preferred stock, shares authorized Preferred Stock Shares Authorized Preferred stock, shares outstanding Preferred Stock Shares Outstanding Common stock, par value Common Stock Par Or Stated Value Per Share Common stock, shares authorized Common Stock Shares Authorized Common stock, shares outstanding Common Stock Shares Outstanding Statement Of Income And Comprehensive Income [Abstract] Revenues: Revenues [Abstract] Total revenues Revenue From Contract With Customer Excluding Assessed Tax Type of revenue [extensible list] Type Of Revenue Extensible List 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): Nonoperating Income Expense [Abstract] Interest income (expense), net Interest Income Expense Nonoperating Net Change in fair value of common stock warrant liability Fair Value Adjustment Of Warrants Other (expense) income, net Other Nonoperating Income Expense Total other income (expense) Nonoperating Income Expense Net loss Net Income Loss Net loss attributable to common stockholders Net Income Loss Available To Common Stockholders Basic Net loss per share attributable to common stockholders—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 Net loss Other comprehensive loss: Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract] Unrealized (losses) gains on marketable securities, net of tax Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax Comprehensive loss Comprehensive Income Net Of Tax Stock issued during period shares at the market offering net. Stock issued during period value at the market offering net. Cumulative effects adjustment from adoption of new accounting standard. Stock issued during period value direct stock placement net. Convertible preferred stock accretion of dividends. Stock issued during period value follow on offering net of offering cost. Stock issued during period value warrant exercise cashless. Statement Of Stockholders Equity [Abstract] Statement [Table] Statement [Table] Class of Stock Statement Class Of Stock [Axis] Class of Stock Class Of Stock [Domain] Convertible Preferred Stock [Member] Convertible Preferred Stock [Member] Adjustments for New Accounting Pronouncements Adjustments For New Accounting Pronouncements [Axis] Type of Adoption Type Of Adoption [Member] ASU 2016-09 [Member] Accounting Standards Update201609 [Member] ASU 2014-09 [Member] Accounting Standards Update201409 [Member] Equity Components Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Stock [Member] Common Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] Accumulated Other Comprehensive Income [Member] Additional Paid-In Capital [Member] Additional Paid In Capital [Member] Accumulated Deficit [Member] Retained Earnings [Member] Series A convertible preferred stock. Series A Convertible Preferred Stock [Member] Series A Convertible Preferred Stock [Member] Statement [Line Items] Statement [Line Items] Beginning balance Temporary Equity Carrying Amount Attributable To Parent Beginning balance, Shares Temporary Equity Shares Outstanding Beginning balance Beginning balance, Shares Shares Outstanding Accretion for convertible preferred stock dividends Temporary Equity Accretion Of Dividends Accretion for convertible preferred stock dividends Convertible Preferred Stock Accretion Of Dividends Proceeds from initial public offering, net of offering costs of $7,186, Value Stock Issued During Period Value New Issues Proceeds from initial public offering, net of offering costs of $7,186, Shares Stock Issued During Period Shares New Issues Conversion of preferred stock into common stock, Value Stock Issued During Period Value Conversion Of Convertible Securities Conversion of preferred stock into common stock, Shares Stock Issued During Period Shares Conversion Of Convertible Securities Reclassification of common stock warrant liability Adjustments To Additional Paid In Capital Warrant Issued Proceeds from follow on offering, net of offering cost of $3,665 Stock Issued During Period Value Follow On Offering Net Of Offering Cost Stock issued during period shares follow on offering net of offering cost. Proceeds from follow on offering, net of offering cost of $3,665, Shares Stock Issued During Period Shares Follow On Offering Net Of Offering Cost Exercise of stock options, Value Stock Issued During Period Value Stock Options Exercised Exercise of stock options, Shares Stock Issued During Period Shares Stock Options Exercised Vesting of restricted stock, Value Stock Issued During Period Value Restricted Stock Award Gross Vesting of restricted stock, Shares Stock Issued During Period Shares Restricted Stock Award Gross Stock-based compensation expense Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Proceeds from "At-the-market" offering, net, Value Stock Issued During Period Value At The Market Offering Net Proceeds from "At-the-market" offering, net, Shares Stock Issued During Period Shares At The Market Offering Net Stock issuance due to warrant exercise, cashless, Value Stock Issued During Period Value Warrant Exercise Cashless Stock issued during period, shares, warrant exercise, cashless. Stock issuance due to warrant exercise, cashless, Shares Stock Issued During Period Shares Warrant Exercise Cashless Stock purchase under ESPP, Value Stock Issued During Period Value Employee Stock Purchase Plan Stock purchase under ESPP, Shares Stock Issued During Period Shares Employee Stock Purchase Plans Unrealized gain (losses) on short-term investments Repurchase of fractional shares resulting from reverse stock splits Adjustments To Additional Paid In Capital Stock Split Employee withholdings ESPP Adjustment To Additional Paid In Capital Income Tax Effect From Share Based Compensation Net Cumulative effect adjustment of adoption ASU Cumulative Effects Adjustment From Adoption Of New Accounting Standard Proceeds from direct stock placement, net, Value Stock Issued During Period Value Direct Stock Placement Net Stock issued during period shares direct stock placement net. Proceeds from direct stock placement, net, Shares Stock Issued During Period Shares Direct Stock Placement Net Retirement of common stock in exchange for common stock warrant Stock Repurchased And Retired During Period Value Retirement of common stock in exchange for common stock warrant, shares Stock Repurchased And Retired During Period Shares Ending balance Ending balance, Shares Ending balance Ending balance, Shares Adjustments to additional paid in capital follow on offering cost. Offering costs Adjustments To Additional Paid In Capital Stock Issued Issuance Costs Follow on offering cost Adjustments To Additional Paid In Capital Follow On Offering Cost Statement Of Cash Flows [Abstract] Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] Follow on public offering. Follow-on Public Offering [Member] Follow On Public Offering [Member] At the market stock offering. At-the-Market Offering [Member] At The Market Stock Offering [Member] Direct Placement Offering [Member] Private Placement [Member] 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] Depreciation Depreciation Amortization and accretion of investments Accretion Amortization Of Discounts And Premiums Investments Stock-based compensation Share Based Compensation Change in fair value of warrants Other Other Noncash Income Expense Changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Prepaid expenses and other assets Increase Decrease In Prepaid Deferred Expense And Other Assets Accounts payable Increase Decrease In Accounts Payable Deferred revenue Increase Decrease In Contract With Customer Liability Accrued expenses and other liabilities Increase Decrease In Accrued Liabilities And Other Operating 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] Purchases of property and equipment Payments To Acquire Property Plant And Equipment Purchases of short-term investments Payments To Acquire Short Term Investments Proceeds from sales and maturities of short-term investments Proceeds From Sale And Maturity Of Available For Sale Securities Net cash provided by (used in) 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 issuance of common stock in initial public offering, net Proceeds From Issuance Initial Public Offering Proceeds from issuance of common stock, net Proceeds From Issuance Of Common Stock Proceeds from Employee Stock Purchase Plan Proceeds From Stock Plans Proceeds from exercise of stock options Proceeds From Stock Options Exercised Other Proceeds From Payments For Other Financing Activities Net cash provided by financing activities Net Cash Provided By Used In Financing Activities NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CASH, CASH EQUIVALENTS AND RESTRICTED CASH—beginning of year Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations CASH, CASH EQUIVALENTS AND RESTRICTED CASH—end of year Organization Consolidation And Presentation Of Financial Statements [Abstract] Nature of Business Nature Of Operations Accounting Policies [Abstract] Basis of Presentation Business Description And Basis Of Presentation [Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Revenue From Contract With Customer [Abstract] Revenue from Contracts with Customers Revenue From Contract With Customer [Text Block] Earnings Per Share [Abstract] Net Loss per Share Attributable to Common Stockholders Earnings Per Share [Text Block] Significant agreements disclosure. Equity [Abstract] Significant Agreements Significant Agreements Disclosure [Text Block] Property Plant And Equipment [Abstract] Property and Equipment, net Property Plant And Equipment Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Measurement Inputs Disclosure [Text Block] Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract] Prepaid Expenses and Other Current Assets Other Current Assets [Text Block] Payables And Accruals [Abstract] Accrued Expenses and Other Current Liabilities Accounts Payable Accrued Liabilities And Other Liabilities Disclosure Current [Text Block] Common stock disclosure. Text Block [Abstract] Common Stock Common Stock Disclosure [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock-Based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments Commitments And Contingencies Disclosure [Text Block] Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Information Cash Flow Supplemental Disclosures [Text Block] Related Party Transactions [Abstract] Related-Party Transactions Related Party Transactions Disclosure [Text Block] Quarterly Financial Information Disclosure [Abstract] Quarterly Financial Information (Unaudited) Quarterly Financial Information [Text Block] Principles of Consolidation Consolidation Policy [Text Block]