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 Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Statement Of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Short-term marketable securities Available For Sale Securities Debt Securities 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 Restricted cash Restricted Cash Noncurrent 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 Deferred revenue Contract With Customer Liability Current Deferred rent Deferred Rent Credit Current Capital lease obligations Capital Lease Obligations Current Total current liabilities Liabilities Current Long-term liabilities: Liabilities Noncurrent [Abstract] Deferred revenue, net of current portion Contract With Customer Liability Noncurrent Deferred rent, net of current portion Deferred Rent Credit Noncurrent Capital lease obligations, net of current portion Capital Lease Obligations Noncurrent Total long-term liabilities Liabilities Noncurrent Commitments and contingencies (Note 14) Commitments And Contingencies Stockholders' Equity Stockholders Equity [Abstract] Preferred stock, $0.001 par value 5,000,000 shares authorized, none issued and outstanding as of June 30, 2018 and December 31, 2017 Preferred Stock Value Common stock, $0.001 par value 250,000,000 shares authorized as of June 30, 2018 and December 31, 2017. 25,432,849 and 16,272,617 shares issued and outstanding as of June 30, 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 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 Issued Preferred Stock Shares Issued Preferred stock, Shares Outstanding Preferred Stock Shares Outstanding Common stock, par value Common Stock Par Or Stated Value Per Share Common stock, authorized Common Stock Shares Authorized Common stock, Issued Common Stock Shares Issued Common stock, 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): Nonoperating Income Expense [Abstract] Interest and investment income Investment Income Nonoperating Interest expense Interest Expense Other expense Other Nonoperating Expense Other income (expense), net Nonoperating Income Expense Net loss Net Income Loss Net loss per share attributable to common shareholders - basic and diluted Earnings Per Share Basic And Diluted Weighted-average common shares used in computing net loss per share attributable to common shareholders - basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Comprehensive loss: Comprehensive Income Net Of Tax [Abstract] Net loss Net unrealized gains (losses) on marketable securities Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent Comprehensive loss Comprehensive Income Net Of Tax Deferred transaction costs. Allowance for tenant improvements. Noncash purchase of property, plant and equipment in accounts payable and accrued liabilities. Assets acquired under capital leases. Equity issuance costs incurred during noncash or partial noncash transaction. Adjustment to transaction costs for amounts included in accounts payable and accrued expenses. Cash Flow Noncash Investing Disclosure [Abstract] Cash Flow Noncash Financing Activities Disclosure [Abstract] 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 in operating activities: Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Depreciation Depreciation Loss on disposal of property and equipment Gain Loss On Sale Of Property Plant Equipment Equity-based compensation expense Share Based Compensation Common shares issued for license acquisition Issuance Of Stock And Warrants For Services Or Claims Accretion/amortization of investment securities Accretion Amortization Of Discounts And Premiums Investments 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 Accounts payable and accrued expenses Increase Decrease In Accounts Payable And Accrued Liabilities Deferred revenue Increase Decrease In Contract With Customer Liability Deferred rent Increase Decrease In Deferred Liabilities Other assets Increase Decrease In Other Operating Assets 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 marketable securities Payments To Acquire Available For Sale Securities Proceeds from maturity of marketable securities Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities Purchases of property and equipment Payments To Acquire Property Plant And Equipment Net cash 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] Payments on capital lease obligations Repayments Of Long Term Capital Lease Obligations Deferred transaction costs Deferred Transaction Costs Proceeds from sale of convertible preferred stock, net of issuance costs Proceeds From Issuance Of Convertible Preferred Stock Proceeds from sale of common stock, net of issuance costs Proceeds From Issuance Of Common Stock Proceeds from sale of preferred units, net of issuance costs Proceeds From Issuance Of Preferred Limited Partners Units 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 at beginning of period Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations Cash, cash equivalents and restricted cash at end of period Supplemental disclosure of non-cash investing activities: Cash Flow Noncash Investing Disclosure [Abstract] Landlord funded allowance for tenant improvements Allowance For Tenant Improvements Property and equipment purchases included in accounts payable and accrued expenses Noncash Purchase Of Property Plant And Equipment In Accounts Payable And Accrued Liabilities Supplemental disclosure of non-cash financing activities: Cash Flow Noncash Financing Activities Disclosure [Abstract] Cash paid for interest Interest Paid Net Purchase under capital lease Assets Acquired Under Capital Leases Issuance costs from sale of preferred shares in accounts payable and accrued expenses Equity Issuance Costs Incurred During Noncash Or Partial Noncash Transaction Adjustment to transaction costs for amounts included in accounts payable and accrued expenses Adjustment To Transaction Costs For Amounts Included In Accounts Payable And Accrued Expenses Organization Consolidation And Presentation Of Financial Statements [Abstract] Nature of Business Organization Consolidation And Presentation Of Financial Statements Disclosure [Text Block] Accounting Policies [Abstract] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Business Combinations [Abstract] Merger with Mirna Therapeutics Mergers Acquisitions And Dispositions Disclosures [Text Block] Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Available for sale securities disclosure. Investments Debt And Equity Securities [Abstract] Available-for-Sale Investments Available For Sale Securities Disclosure [Text Block] Property Plant And Equipment [Abstract] Property and Equipment, Net Property Plant And Equipment Disclosure [Text Block] Payables And Accruals [Abstract] Accrued Expenses Accounts Payable Accrued Liabilities And Other Liabilities Disclosure Current [Text Block] Equity [Abstract] Common Stock Stockholders Equity Note Disclosure [Text Block] Preferred Stock Preferred Stock [Text Block] Preferred units. Preferred Units Preferred Units [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Equity-based Compensation and Equity Incentive Plans Disclosure Of Compensation Related Costs Share Based Payments [Text Block] AbbVie Collaboration Agreement Collaborative Arrangement Disclosure [Text Block] Earnings Per Share [Abstract] Net Loss per Share Earnings Per Share [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Principles of Consolidation Consolidation Policy [Text Block] Recently adopted accounting pronouncements. Recently Adopted Accounting Pronouncements Recently Adopted Accounting Pronouncements Policy [Text Block] Recently Issued Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block] Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis Schedule Of Fair Value Assets And Liabilities Measured On Recurring Basis Table [Text Block] Summary of Available-for-Sale Securities Held Schedule Of Available For Sale Securities Reconciliation Table [Text Block] Schedule of Property and Equipment, Net Property Plant And Equipment [Text Block] Schedule of Accrued Expenses Schedule Of Accrued Liabilities Table [Text Block] Statement [Table] Statement [Table] Plan Name Plan Name [Axis] Plan Name Plan Name [Domain] Long term incentive plan 2015 and 2017. 2015 and 2017 Plan Long Term Incentive Plan2015 And2017 [Member] Statement [Line Items] Statement [Line Items] Schedule of Stock Option Activity Schedule Of Share Based Compensation Stock Options Activity Table [Text Block] Schedule of share based compensation restricted stock award activity. Schedule of Restricted Common Stock Activity Schedule Of Share Based Compensation Restricted Stock Award Activity Table [Text Block] Schedule of Equity-based Compensation Expenses Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Schedule of Equity-based Compensation Expenses by Award Type Disclosure Of Share Based Compensation Arrangements By Share Based Payment Award [Text Block] Schedule of Potentially Common Shares Excluded from Calculation of Net Loss Per share Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Nature of business. Nature of business. Nature Of Business [Table] Nature Of Business [Table] Equity Components Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Stock Common Stock [Member] Sale of Stock Subsidiary Sale Of Stock [Axis] Sale of Stock Sale Of Stock Name Of Transaction [Domain] Direct Offering Private Placement [Member] Nature Of Business [Line Items] Nature Of Business [Line Items] Number of operating segment Number Of Operating Segments Cash, cash equivalents, and marketable securities Cash Cash Equivalents And Short Term Investments Stock sold and issued to investors Stock Issued During Period Shares New Issues Stock sold and issued to investors, per share Share Price Net proceeds from sale of common stock Summary of significant accounting policies. Summary of significant accounting policies. Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Adjustments for New Accounting Pronouncements Adjustments For New Accounting Pronouncements [Axis] Type of Adoption Type Of Adoption [Member] ASC 606 Accounting Standards Update201409 [Member] Initial Application Period Cumulative Effect Transition Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition Initial Application Period Cumulative Effect Transition [Domain] Impact as Result of Adoption of ASC 606 Difference Between Revenue Guidance In Effect Before And After Topic606 [Member] Balances without Adoption of ASC 606 Calculated Under Revenue Guidance In Effect Before Topic606 [Member] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Revenue, practical expedient, incremental cost of obtaining contract [true/false] Revenue Practical Expedient Incremental Cost Of Obtaining Contract Revenue, practical expedient, remaining performance obligation, description Revenue Practical Expedient Remaining Performance Obligation Description Cumulative-effect decrease to opening accumulated deficit Deferred revenue Contract With Customer Liability Common Stock Exchange Ratio Number of members on board of directors. Schedule Of Business Acquisitions By Acquisition [Table] Schedule Of Business Acquisitions By Acquisition [Table] Business Acquisition Business Acquisition [Axis] Business Acquisition, Acquiree Business Acquisition Acquiree [Domain] Mirna Therapeutics [Member] Mirna therapeutics Mirna Therapeutics [Member] Consolidated Entities Consolidated Entities [Axis] Consolidated Entities Consolidated Entities [Domain] Synlogic Parent Company [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Business combination date Business Acquisition Effective Date Of Acquisition1 Reserve stock split of common stock prior to its merger Stockholders Equity Note Stock Split Conversion Ratio1 Exchange ratio of common stock Common Stock Exchange Ratio Common stock outstanding Share ownership following merger, percent Subsidiary Or Equity Method Investee Cumulative Percentage Ownership After All Transactions Number of members on Board of Directors Number Of Members On Board Of Directors Fair Value Asset Measured On Recurring Basis [Line Items] Fair Value Asset Measured On Recurring Basis [Table] Fair Value Asset Measured On Recurring Basis [Table] Fair Value Asset Measured On Recurring Basis [Table] Measurement Frequency Fair Value By Measurement Frequency [Axis] Fair Value, Measurement Frequency Fair Value Measurement Frequency [Domain] Recurring Fair Value Measurements Recurring [Member] Cash and Cash Equivalents Cash And Cash Equivalents [Axis]