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 Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Statement Of Financial Position [Abstract] Statement [Table] Statement [Table] Class of Stock Statement Class Of Stock [Axis] Class of Stock Class Of Stock [Domain] Convertible Preferred Stock Convertible Preferred Stock [Member] Statement [Line Items] Statement [Line Items] Assets Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Short-term investments Available For Sale Securities Debt 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 Property and equipment, net Property Plant And Equipment Net Intangible assets, net Indefinite Lived Intangible Assets Excluding Goodwill Goodwill Goodwill Restricted cash Restricted Cash Noncurrent Other assets Other Assets Noncurrent Total assets Assets Current liabilities: Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued liabilities Accrued Liabilities Current Income tax payable Taxes Payable Current Deferred revenues, current portion Contract With Customer Liability Current Total current liabilities Liabilities Current Deferred revenue, net of current portion Contract With Customer Liability Noncurrent Other long-term liabilities Other Liabilities Noncurrent Total liabilities Liabilities Commitments and contingencies (Note 11) Commitments And Contingencies Stockholders' equity Stockholders Equity [Abstract] Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized at December 31, 2018 and 2017; no shares issued and outstanding at December 31, 2018 and 2017, respectively Preferred Stock Value Common stock, $0.00001 par value; 75,000,000 shares authorized at December 31, 2018 and 2017; 45,083,209 and 38,478,560 shares issued and outstanding at December 31, 2018 and 2017, respectively Common Stock Value Additional paid-in capital Additional Paid In Capital Accumulated other comprehensive loss Accumulated Other Comprehensive Income Loss Net Of Tax Accumulated deficit Retained Earnings Accumulated Deficit Total stockholders' equity Stockholders Equity Total liabilities, convertible preferred stock and stockholders' equity Liabilities And Stockholders Equity Convertible Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Convertible Preferred stock, shares authorized Preferred Stock Shares Authorized Convertible Preferred stock, shares issued Preferred Stock Shares Issued Convertible 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 issued Common Stock Shares Issued Common stock, shares outstanding Common Stock Shares Outstanding Statement Of Income And Comprehensive Income [Abstract] Revenues Revenue From Contract With Customer Excluding Assessed Tax Type of Revenue [Extensible List] Type Of Revenue Extensible List Revenues from related parties Revenue From Related Parties Total 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 Interest income Investment Income Interest Other income (expense), net Other Nonoperating Income Expense Loss before income taxes Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest Provision for (benefit from) income taxes Income Tax Expense Benefit Net loss Net Income Loss Net loss per share, basic and diluted Income Loss From Continuing Operations Per Basic And Diluted Share Shares used to compute net loss per share, basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Other comprehensive loss: Other Comprehensive Income Loss Tax [Abstract] Changes in unrealized gain (losses) on investments Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax Total comprehensive loss Comprehensive Income Net Of Tax Adjustments on stockholders note. Number of shares issued during the period as a result of an stock purchase agreement. Aggregate change in value for stock issued during the period as a result of stock purchase agreement. Statement Of Stockholders Equity [Abstract] Equity Components Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Stock Common Stock [Member] Stockholder Notes Receivables From Stockholder [Member] Additional Paid-in Capital Additional Paid In Capital [Member] Accumulated Other Comprehensive Income/(Loss) Accumulated Other Comprehensive Income [Member] Accumulated Deficit Retained Earnings [Member] Beginning balance Beginning balance, shares Shares Issued Impact of adoption of new accounting pronouncements Cumulative Effect On Retained Earnings Net Of Tax1 Issuance of common stock in follow-on offering, net of issuance costs Stock Issued During Period Value New Issues Issuance of common stock in follow-on offering, net of issuance costs, shares Stock Issued During Period Shares New Issues Exercise of stock options Stock Issued During Period Value Stock Options Exercised Exercise of stock options, shares Stock Issued During Period Shares Stock Options Exercised Issuance of common stock under the Employee Stock Purchase Plan Stock Issued During Period Value Employee Stock Purchase Plan Issuance of common stock under the Employee Stock Purchase Plan, shares Stock Issued During Period Shares Employee Stock Purchase Plans Issuance of common stock in connection with services Stock Issued During Period Value Issued For Services Issuance of common stock in connection with services, shares Stock Issued During Period Shares Issued For Services Issuance of common stock pursuant to the Amgen Stock Purchase Agreement Stock Issued During Period Value Stock Purchase Agreement Issuance of common stock pursuant to the Amgen Stock Purchase Agreement, shares Stock Issued During Period Shares Stock Purchase Agreement Repayment on stockholders note Adjustments On Stockholders Note Stock-based compensation Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Other comprehensive income (loss) Other Comprehensive Income Loss Net Of Tax Net loss Ending balance Ending balance, shares Increase (decrease) in accrued liabilities and other liabilities noncurrent. Proceeds from stockholder notes. Statement Of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided By Used In Operating Activities [Abstract] Adjustments to reconcile net loss to net cash (used) provided by operating activities: Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Loss/(gain) on disposal of property and equipment Gain Loss On Sale Of Property Plant Equipment Depreciation and amortization Depreciation And Amortization Amortization of premium (accretion of discount) on investments Accretion Amortization Of Discounts And Premiums Investments Stock-based compensation expense Share Based Compensation Issuance of common stock in connection with services Issuance Of Stock And Warrants For Services Or Claims Non-cash acquisition of in process research and development asset charged to expense Research And Development In Process Deferred income taxes Deferred Income Taxes And Tax Credits Changes in operating assets and liabilities Increase Decrease In Operating Capital [Abstract] Accounts receivable Increase Decrease In Accounts Receivable Related party accounts receivable Increase Decrease In Accounts Receivable Related Parties Prepaid expenses and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Other assets Increase Decrease In Other Operating Assets Accounts payable Increase Decrease In Accounts Payable Accrued liabilities and other liabilities Increase Decrease In Accrued Liabilities And Other Liabilities Noncurrent Deferred revenue Increase Decrease In Contract With Customer Liability Net cash (used in) provided by 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 Proceeds from sales of assets Proceeds From Sale Of Productive Assets Purchases of short term investments Payments To Acquire Available For Sale Securities Debt Maturities of short term investments Proceeds From Sale Of Available For Sale Securities Debt 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, net of issuance costs Proceeds From Issuance Of Common Stock Proceeds from employee stock purchases and exercise of stock options Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options Proceeds from stockholder notes Proceeds From Stockholder Notes Payment of deferred offering costs Payment Of Financing And Stock Issuance Costs Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Net increase in cash and cash equivalents Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect Cash, cash equivalents and restricted cash, beginning of year Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Cash, cash equivalents and restricted cash, end of year Supplemental disclosures of noncash investing and financing items: Noncash Investing And Financing Items [Abstract] Purchases of property and equipment in accounts payable and accrued liabilities Capital Expenditures Incurred But Not Yet Paid Disclosure Text Block [Abstract] Description of the Business Nature Of Operations Accounting Policies [Abstract] Basis of Presentation and Summary of Significant Accounting Policies Basis Of Presentation And Significant Accounting Policies [Text Block] Adopted and recent accounting pronouncements. Adopted and Recent Accounting Pronouncements Adopted And Recent Accounting Pronouncements [Text Block] Earnings Per Share [Abstract] Net Loss Per Share Attributable to Common Stockholders Earnings Per Share [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements and Short-Term Investments Fair Value Disclosures [Text Block] Property Plant And Equipment [Abstract] Property and Equipment Property Plant And Equipment Disclosure [Text Block] Goodwill And Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Goodwill And Intangible Assets Disclosure [Text Block] Accrued Liabilities Current [Abstract] Accrued Liabilities Accounts Payable And Accrued Liabilities Disclosure [Text Block] Research and collaboration agreements. Organization Consolidation And Presentation Of Financial Statements [Abstract] Research and Collaboration Agreements Research And Collaboration Agreements [Text Block] License agreement. Research And Development [Abstract] License Agreement License Agreement Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Equity [Abstract] Common Stock Stockholders Equity Note 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] Related Party Transactions [Abstract] Related Party Transactions Disclosure Related Party Transactions Disclosure [Text Block] Compensation And Retirement Disclosure [Abstract] Defined Contribution Plan Pension And Other Postretirement Benefits Disclosure [Text Block] Quarterly Financial Information Disclosure [Abstract] Supplementary Data – Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Subsequent Events [Abstract] Subsequent Event Subsequent Events [Text Block] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Use of Estimates Use Of Estimates Concentration of Credit Risk and Other Risks and Uncertainties Concentration Risk Credit Risk Segments Segment Reporting Policy Policy [Text Block] Cash and Cash Equivalents Cash And Cash Equivalents Policy [Text Block] Restricted Cash Cash And Cash Equivalents Restricted Cash And Cash Equivalents Policy Short-term Investments Marketable Securities Policy Property and Equipment, net Property Plant And Equipment Policy [Text Block] Goodwill and Intangible Assets Goodwill And Intangible Assets Policy [Text Block] Impairment of Long-Lived Assets Impairment Or Disposal Of Long Lived Assets Policy [Text Block] Revenue Recognition Revenue Recognition Policy [Text Block] Comprehensive Loss Comprehensive Income Policy Policy [Text Block] Contract Balances Revenue From Contract With Customer Policy [Text Block] Stock-Based Compensation Share Based Compensation Option And Incentive Plans Policy Income Taxes Income Tax Policy [Text Block] Accrued Research and Development Costs Research And Development Expense Policy Reclassifications Prior Period Reclassification Adjustment Description Adopted Accounting Pronouncements and Recent Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block]