Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Type of Arrangement and Non-arrangement Transactions [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] Arrangements and Non-arrangement Transactions [Domain] Arrangements and Non-arrangement Transactions [Domain] MIT Exclusive Patent License Agreement With Massachusetts Institute Of Technology [Member] Represents information pertaining to Exclusive patent license agreement with Massachusetts Institute of Technology. " Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Research and Development Arrangement, Contract to Perform for Others, Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type [Domain] Research and Development Arrangement, Contract to Perform for Others, Type [Domain] Spark License Agreement License Agreement Terms [Member] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Percentage of sublicense income Percentage Of Sublicense Income Represents information pertaining to percentage of sublicense income. Payment amount upon achievement of defined clinical milestones Payment Amount Upon Achievement Of Defined Clinical Milestones Represents information pertaining to payment amount upon achievement of defined clinical milestones. Contractual payments defined in the Exclusive Patent License agreement License And Option Agreement, Contractual Payments Made License And Option Agreement, Contractual Payments Made License and option agreement, payments made relative to calculated premium paid for initial equity investment made under the purchase agreement License And Option Agreement, Calculated Premium Paid For Equity Investment Under Purchase Agreement License And Option Agreement, Calculated Premium Paid For Equity Investment Under Purchase Agreement Equity [Abstract] Common Stock Stockholders' Equity Note Disclosure [Text Block] Investments, Debt and Equity Securities [Abstract] Fair Value Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract] Less than one year Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Amortized Cost Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract] Less than one year Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Commitments and Contingencies Disclosure [Abstract] Year ended December 31, Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years Total minimum lease payments Operating Leases, Future Minimum Payments Due Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Domain] Lease Arrangement, Type [Domain] Laboratory and office space Laboratory And Office Space [Member] Represents information pertaining to laboratory and office space member. Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Restricted cash and other deposits Restricted Cash And Other Deposits [Member] Represents inforamtion pertaining to restricted cash and other deposits member. Accrued expenses Accounts Payable and Accrued Liabilities [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Letter of credit Letter of Credit [Member] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Tenant improvement allowance Payments for (Proceeds from) Tenant Allowance Letter of credit Line of Credit Facility, Maximum Borrowing Capacity Area of additional office space leased Area of Real Estate Property Deferred rent and lease incentive liability Deferred Rent And Lease Incentive Liability This element represents both current and non current costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease and includes the deferred charge for an incentive or inducement granted by a lessor to a lessee, in order to motivate the lessee to enter the lease agreement, which incentive or inducement is to be recognized as a reduction of rental revenue over the lease term. Current portion of deferred rent and lease incentive liability (less than) Accrued Rent And Lease Incentive Payable Current " Carrying value as of the balance sheet date of obligations incurred through that date and payable for contractual rent under lease arrangements and an incentive or inducement contractually stipulated between parties to a lease whereby the lessor has committed to provide the entity (lessee) with a cash payment as inducement to enter the lease. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer)." Rent expense, net of sublease payments Operating Leases, Rent Expense, Net Quarterly Financial Information Disclosure [Abstract] Grant and collaboration revenue Revenues Operating expenses Operating Expenses Net loss Net Income (Loss) Attributable to Parent Accretion of redeemable convertible preferred stock Temporary Equity, Accretion to Redemption Value, Adjustment Net (loss) income attributable to common stockholders - basic & diluted Net Income (Loss) Available to Common Stockholders, Basic Net loss per share attributable to common stockholders—basic and diluted (in dollars per share) Earnings Per Share, Basic and Diluted Earnings Per Share [Abstract] Computation of Basic and Diluted Net Loss Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Potential Common Shares Issuable Upon Conversion of Warrants Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Revenue Recognition [Abstract] Sanofi Sanofi Collaboration Agreement [Member] Represents information pertaining to collaboration agreement with Sanofi. Aggregate payments under Sanofi Agreement Aggregate Amount Of Upfront And Milestone Based Payments Represents information pertaining to aggregate amount of upfront and milestone based payments. Remaining revenue recognized Deferred Revenue, Revenue Recognized Property, Plant and Equipment [Abstract] Depreciation expense Depreciation Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Tranche One Share-based Compensation Award, Tranche One [Member] Tranche Two Share-based Compensation Award, Tranche Two [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2008 Plan Stock Incentive Plan2008 [Member] Represents the information pertaining to the 2008 stock incentive plan, which provides for the granting of stock based awards to employees, directors, and consultants under terms and provisions established by the board of directors. 2016 Plan Stock Incentive Plan2016 [Member] Represents the information pertaining to the 2016 stock incentive plan, which provides for the granting of stock based awards to employees, directors, and consultants under terms and provisions established by the board of directors. Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Shares available for future stock incentive awards Stock Compensation Plan [Member] Non-employee stock options Non Employee Stock Option [Member] An arrangement whereby a non-employee is entitled to receive in the future, subject to vesting and other restrictions, a number of shares in the entity at a specified price, as defined in the agreement. Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of shares authorized for grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Automatic increase in the number of shares that may be issued (as a percent) Employee Stock Purchase Plan Maximum Percentage Of Shares Reserved Based On Shares Outstanding The maximum percentage increase in the shares reserved for future issuance each year based on the number of common stock outstanding at the last day of the year. Number of shares available for future grants Common Stock, Capital Shares Reserved for Future Issuance Exercise price of incentive stock options (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent Combined voting power of participants (as a percent) Share-based Compensation Arrangement By Share-based Payment Award, Voting Rights of Common Stock, Holding Percentage Represents the percentage of voting rights of all classes of stock held by the employees. Award vesting term Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Award expiration term Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Estimated forfeitures rate Share-based Compensation Arrangement By Share-based Payment Award Forfeitures Rate Represents the percentage of forfeitures rate of the stock options based on the historical trends. Weighted average grant date fair value of stock options (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Aggregate intrinsic value of stock options exercised (less than in 2016) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Unrecognized compensation expense related to unvested employee stock options Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options Weighted average period for recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Unvested stock option awards (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Unrecognized compensation expense related to unvested non-employee stock options Share-Based Goods And Non Employee Services Transaction, Compensation Not Yet Recognized, Stock Options Share-Based Goods And Non Employee Services Transaction, Compensation Not Yet Recognized, Stock Options Stock‑based compensation expense Allocated Share-based Compensation Expense Shares exercises in period by employees Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Schedule of Share-based Goods and Nonemployee Services Transaction [Table] Schedule of Share-based Goods and Nonemployee Services Transaction [Table] Share-based Goods and Nonemployee Services Transaction [Line Items] Share-based Goods and Nonemployee Services Transaction [Line Items] Risk‑free interest rate Share-based Goods and Nonemployee Services Transaction, Valuation Method, Risk Free Interest Rate Expected dividend yield (as a percent) Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Dividend Rate Expected term Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Term Expected volatility (as a percent) Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Volatility Rate Technology License Agreements Technology License Agreements [Text Block] The entire disclosure for technology license agreements. Net Loss Per Share Earnings Per Share [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Nature of the Business and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Other Research And Collaboration Agreements Other Research And Collaboration Agreements [Member] Represents information pertaining to other research and collaboration agreements. Revenue recognized (less than in 2016) Research and Development Arrangement, Contract to Perform for Others, Compensation Earned Debt Disclosure [Abstract] Debt Conversion [Table] Debt Conversion [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Conversion of Series E Preferred Series E Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series E redeemable convertible preferred stock. Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Convertible notes Convertible Notes Payable [Member] Debt Conversion [Line Items] Debt Conversion [Line Items] Convertible notes interest rate per annum Debt Instrument, Interest Rate, Stated Percentage Percentage of convertible notes for which warrants were issued to purchase common stock Percentage Of Convertible Notes For Which Warrants Issued To Purchase Common Stock Percentage Of Convertible Notes For Which Warrants Issued To Purchase Common Stock Exercise price (in dollars per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Warrants issued for purchase of stock (in shares) Class of Warrant or Right, Number of Securities Called by Warrants or Rights Expiration period of warrants Class Of Warrants Or Rights, Term Period of time between issuance and maturity of warrant, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Shares issued on conversion of outstanding convertible notes (in shares) Debt Conversion, Converted Instrument, Shares Issued Interest expense related to convertible notes Interest Expense, Debt Payables and Accruals [Abstract] Accrued Expenses Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Schedule of Property and Equipment Property, Plant and Equipment [Table Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Exercise of common warrants Warrant [Member] Outstanding common stock options Employee Stock Option [Member] Class of Stock [Line Items] Class of Stock [Line Items] Total (in shares) Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Springer Purchase Agreement Springer Purchase Agreement [Member] Springer Purchase Agreement [Member] Stock warrants to purchase common stock Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Landlord Landlord [Member] Represents information pertaining to landlord member. Founders Founder [Member] Represents information pertaining to founder member. Series B Preferred Series B Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series B redeemable convertible preferred stock. Series D Redeemable Convertible Preferred Stock Series D Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series D redeemable convertible preferred stock. Common stock Common Stock [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Stock issued (in shares) Stock Issued During Period, Shares, New Issues Share price (in dollars per share) Shares Issued, Price Per Share Total proceeds Proceeds from Issuance of Convertible Preferred Stock Bridge loan Bridge Loan Sale of stock, price per share Sale of Stock, Price Per Share Sale of stock, number of shares issued in transaction Sale of Stock, Number of Shares Issued in Transaction Share price Class of Warrant or Right, Issued to Purchase Common Stock Class of Warrant or Right, Issued to Purchase Common Stock Expenses for consulting services Related Party Transaction, Expenses from Transactions with Related Party Number of investment positions Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Fair value of investments, unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Number of investment position in an unrealized loss position, less than twelve months Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year Fair value investments, unrealized loss position, less than twelve months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Other-than-temporary impairments Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Selected Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Retirement Benefits [Abstract] 401(k) Savings Plan Pension and Other Postretirement Benefits Disclosure [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Term Loans Term Loan [Member] Represents information pertaining to term loan member. 2017 Term Loans 2017 Term Loans [Member] 2017 Term Loans [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Convertible Debt Convertible Debt [Member] Debt Covenant Period [Axis] Debt Covenant Period [Axis] Debt Covenant Period [Axis] Debt Covenant Period [Domain] Debt Covenant Period [Domain] [Domain] for Debt Covenant Period [Axis] Term Loan Prepaid Before the First Anniversary [Member] Term Loan Prepaid Before the First Anniversary [Member] Term Loan Prepaid Before the First Anniversary [Member] Prepaid after to first anniversary but before second Term Loan Prepaid After First Anniversary But Before Second Anniversary [Member] Represents information pertaining to prepayment of term loan after first anniversary but prior to second anniversary. Prepaid after second anniversary Term Loan Prepaid After Second Anniversary [Member] Represents information pertaining to prepayment of term loan after second anniversary. Conversion of Series D Preferred Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Borrowing capacity Borrowings on loan and security agreement Proceeds from Lines of Credit Interest rate per annum Line of Credit Facility, Interest Rate During Period Number of monthly installments Debt Instrument, Term Prepayment fee (as a percent) Early Extinguishment Of Debt, Prepayment Fee Percentage Percentage of fee payable on early extinguishment of debt. Final payment fee (as a percent) Final Payment Fee Percentage Percentage of final fee payment payable on aggregate principal amounts borrowed. Final payment fee Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid Initial grant date fair value of warrants Warrants, Grant Date Fair Value Represents the initial grant date fair value of the warrants. Number of warrants exercised to purchase common stock (in shares) Number Of Warrants Exercised To Purchase Common Stock Number Of Warrants Exercised To Purchase Common Stock Net shares of common stock issued (in shares) Stock Issued During Period, Shares, Common Stock Issued Upon Exercise Of Warrants Stock Issued During Period, Shares, Common Stock Issued Upon Exercise Of Warrants Outstanding principal balance under Term Loans Long-term Line of Credit Repayments of Lines of Credit Repayments of Lines of Credit Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Debt Issuance Costs, Line of Credit Arrangements, Net Debt Issuance Costs, Line of Credit Arrangements, Net Minimum assets trigger Debt Instrument, Event Of Default, Minimum Assets Trigger Debt Instrument, Event Of Default, Minimum Assets Trigger Minimum amount in excess of indebtedness trigger Debt Instrument, Event Of Default, Minimum Amount In Excess Of Indebtedness Trigger Debt Instrument, Event Of Default, Minimum Amount In Excess Of Indebtedness Trigger Interest expense related to the Term Loan Interest Expense Accounting Policies [Abstract] Effective interest rate for debt arrangement Debt Instrument, Interest Rate, Effective Percentage Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Corporate Bonds Corporate Bond Securities [Member] U.S. government agency bonds US Treasury and Government [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] Tri-party repurchase agreements collateralized by government securities (not less than) (as a percent) Cash And Cash Equivalents Collateralized By Government Securities, Value Of Collateral, Percent Of Fair Value Cash And Cash Equivalents Collateralized By Government Securities, Value Of Collateral, Percent Of Fair Value Average maturity, term Investments Maturity Period Represents information pertaining to US treasury obligations in investments maturity period. Available-for-Sale Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Schedule of Cash and Cash Equivalents [Table] Schedule of Cash and Cash Equivalents [Table] Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Agreements collateralized by U.S. treasury securities (no less than) (as a percent) Realized gains or losses on sale of investments Realized Investment Gains (Losses) Reverse stock split Stockholders' Equity Note, Stock Split, Conversion Ratio 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] Stock options and restricted common stock Stock Options And Restricted Common Stock [Member] Stock Options And Restricted Common Stock [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Research and development Research And Development [Member] Represents the information pertaining to research and development expenses included in the income statement. General and administrative General and Administrative Expense [Member] 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] Total Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Foreign currency translation adjustment Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Unrealized gains (losses) on available-for-sale securities Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Accumulated other comprehensive income (loss) AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance Stockholders' Equity Attributable to Parent Other comprehensive loss during the year Other Comprehensive Income (Loss), Net of Tax Ending balance Schedule of Quarterly Financial Information Quarterly Financial Information [Table Text Block] Income Tax Disclosure [Abstract] Components of Deferred Tax Assets [Abstract] Deferred tax assets Deferred Tax Assets, Gross [Abstract] Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Research and development credits Deferred Tax Assets, Tax Credit Carryforwards, Research Stock-based compensation expense Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Deferred rent and other expenses Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals Deferred revenue Deferred Tax Assets, Deferred Income Patent costs/amortization Deferred Tax Assets, Goodwill and Intangible Assets Total deferred tax assets Deferred Tax Assets, Gross Deferred tax liabilities Deferred Tax Liabilities, Gross [Abstract] Depreciation Deferred Tax Liabilities, Property, Plant and Equipment Debt discount Deferred Tax Liabilities, Deferred Expense, Debt Issuance Costs Unrealized foreign exchange gain Deferred Tax Liabilities, Unrealized Currency Transaction Gains Total deferred tax liabilities Deferred Tax Liabilities, Gross Net deferred tax assets Deferred Tax Assets, Net Of Deferred Tax Liabilities Deferred Tax Assets, Net Of Deferred Tax Liabilities Valuation allowance Deferred Tax Assets, Valuation Allowance Net deferred tax assets Deferred Tax Assets, Net Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring Fair Value, Measurements, Recurring [Member] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Money market funds Money Market Funds [Member] Tri-party repurchase agreements Repurchase Agreements [Member] Corporate bonds Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] (Level 1) Fair Value, Inputs, Level 1 [Member] (Level 2) Fair Value, Inputs, Level 2 [Member] (Level 3) Fair Value, Inputs, Level 3 [Member] Included in cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Included in investments Investments, Fair Value Disclosure 3SBio License License Agreement With Shenyang Sunshine Pharmaceutical Company Limited [Member] Represents information pertaining to License agreement with Shenyang Sunshine Pharmaceutical co., ltd. Period after approval to commercialize product Period For Commercialization Of Product Represents information pertaining to period for commercialization of product. Aggregate amount of upfront and milestone-based payments Aggregate Amount Of Upfront And Milestone Based Payments Paid Aggregate Amount Of Upfront And Milestone Based Payments Paid Additional liability for milestone payments expensed in 2016 Upfront And Milestone Based Payments, Additional Liability Upfront And Milestone Based Payments, Additional Liability Aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for products containing SVP technology Aggregate Amount For Future Payments Upon Achievement Of Clinical And Regulatory Approval Milestones For Products Containing Svp Technology Represents information pertaining to aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for product containing SVP technology. Aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for products without SVP technology Aggregate Amount For Future Payments Upon Achievement Of Clinical And Regulatory Approval Milestones For Products Without Svp Technology Represents information pertaining to aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for product without SVP technology. Maximum paid on tiered royalties (percent) Maximum Percentage Paid On Tiered Royalties Maximum Percentage Paid On Tiered Royalties Period for prior written notice to terminate license Period For Prior Written Notice To Terminate License Represents information pertaining to period for prior written notice to terminate license. Schedule of Accrued Expenses Schedule of Accrued Liabilities [Table Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Year ended December 31, Long-term Debt, Fiscal Year Maturity [Abstract] 2018 Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four 2022 Long-term Debt, Maturities, Repayments of Principal in Year Five Total minimum debt payments Long-term Debt Less: Amount representing interest Debt Instrument Interest Portion The interest portion of gross outstanding debt. Less: Debt discount and deferred charges Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Less: Current portion of loans payable Long-term Debt, Current Maturities Loans payable, net of current portion Long-term Debt, Excluding Current Maturities Summary of Available-for-Sale Marketable Securities Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Schedule of Fair Values and Amortized Cost of Marketable Debt Securities by Contractual Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Summary of Assets Measured at Fair Value on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Research and Development Arrangement, Contract to Perform for Others [Table] Schedule of Research and Development Arrangement, Contract to Perform for Others [Table] Spark Letter Agreement Spark Letter Agreement [Member] Spark Letter Agreement [Member] Research and Development Arrangement, Contract to Perform for Others [Line Items] Research and Development Arrangement, Contract to Perform for Others [Line Items] Number of shares authorized to be issued pursuant to the Stock Purchase Agreement Stock Purchase Program, Number Of Shares Authorized To Be Sold Stock Purchase Program, Number Of Shares Authorized To Be Sold Aggregate purchase price Aggregate Purchase Price Aggregate Purchase Price Aggregate purchase price per share (in dollar per share) Stock Purchase Program, Aggregate Purchase Price Per Share Stock Purchase Program, Aggregate Purchase Price Per Share Premium of average daily VWAP (as a percent) Premium Of Average Daily Volume Weighted Average Price Of Common Stock, Percent Premium Of Average Daily Volume Weighted Average Price Of Common Stock, Percent Issuance of common stock, license agreement Stock Issued During Period, Value, Purchase of Assets Sale common stock Sale of Stock, Consideration Received on Transaction Consecutive calendar days leading up to and ending on the day prior to the Contract Date Consecutive Calendar Days Leading Up To Contract Date Consecutive Calendar Days Leading Up To Contract Date Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Laboratory equipment Laboratory Equipment [Member] Represents information pertaining to laboratory equipment. Computer equipment and software Computer Equipment [Member] Leasehold improvements Leasehold Improvements [Member] Furniture and fixtures Furniture and Fixtures [Member] Office equipment Office Equipment [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Total property and equipment Property, Plant and Equipment, Gross Less accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property and equipment, net Property, Plant and Equipment, Net Accumulated deficit Retained Earnings (Accumulated Deficit) Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Russian subsidiary RUSSIAN FEDERATION Unrestricted cash Unrestricted Cash [Member] Unrestricted Cash [Member] Unrestricted cash held by subsidiary Cash and Cash Equivalents, at Carrying Value Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] At-The-Market Offering [Member] At-The-Market Offering [Member] At-The-Market Offering [Member] 2017 PIPE 2017 PIPE [Member] 2017 PIPE [Member] IPO IPO [Member] Over-Allotment Option Over-Allotment Option [Member] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Public securities offering, amount authorized Public Securities Offering, Amount Authorized Public Securities Offering, Amount Authorized Public stock offering, amount authorized Public Stock Offering, Amount Authorized Public Stock Offering, Amount Authorized Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Proceeds from Initial Public Offering, net of underwriters' discounts and commissions Proceeds from Issuance Initial Public Offering Common stock issued for convertible preferred stock (in shares) Convertible Preferred Stock, Shares Issued upon Conversion Common stock, shares authorized Common Stock, Shares Authorized Number of votes per share that common stockholders are entitled to Votes Per Share of Common Stock Votes Per Share of Common Stock Dividends declared or paid on common stock Dividends, Common Stock Common stock, shares outstanding Common Stock, Shares, Outstanding Related-Party Transactions Related Party Transactions Disclosure [Text Block] Components of Accumulated Other Comprehensive Income (Loss), Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Income Taxes Income Tax Disclosure [Text Block] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Tax Effects of Temporary Differences Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Revenue Arrangements Collaborative Arrangement Disclosure [Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [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 Amortization of premiums and accretion of discounts on investments Accretion (Amortization) of Discounts and Premiums, Investments Loss on disposal of fixed assets Gain (Loss) on Disposition of Property Plant Equipment Non‑cash interest expense Paid-in-Kind Interest Loss on extinguishment of debt Change in fair value of redeemable convertible preferred stock warrant Fair Value Adjustment of Warrants Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Restricted cash and other deposits Increase (Decrease) in Restricted Cash for Operating Activities Accounts payable Increase (Decrease) in Accounts Payable Deferred revenue Increase (Decrease) in Deferred Revenue Contingently repayable grant funding Increase Decrease In Contingently Repayable Grant Funding The increase (decrease) during the reporting period in contingently repayable grant funding that are used in an entity's business. 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, Continuing Operations [Abstract] Maturities of short-term government obligations Proceeds from Maturities, Prepayments and Calls of Short-term Investments Purchase of short-term investments Payments to Acquire Short-term Investments Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Proceeds from the sale of property and equipment Proceeds from Sale of 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, Continuing Operations [Abstract] Proceeds from issuance of long-term debt, net of expenses Repayments of long-term debt Repayments of Long-term Debt Proceeds from issuance of convertible note Proceeds from Convertible Debt Deferred IPO costs paid Payments of Stock Issuance Costs Proceeds from Private Placement, net of issuance costs ($2.9 million) Proceeds from Issuance of Private Placement Proceeds from issuance of common stock Proceeds from exercise of stock options Proceeds from Stock Options Exercised Proceeds from issuance of common stock under Employee Stock Purchase Plan Proceeds from Stock Plans Net proceeds from issuance of preferred stock and warrants Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Effect of exchange rate changes on cash Effect of Exchange Rate on Cash and Cash Equivalents, Continuing Operations Net increase 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 Supplement cash flow information Supplemental Cash Flow Information [Abstract] Cash paid for interest Interest Paid Noncash investing and financing activities Noncash Investing and Financing Items [Abstract] Purchase of property and equipment not yet paid Capital Expenditures Incurred but Not yet Paid Unrealized gain on marketable securities Marketable Securities, Unrealized Gain (Loss) Venture debt termination fee liability Noncash Investing And Financing Activities, Venture Debt Termination Fee Liability Noncash Investing And Financing Activities, Venture Debt Termination Fee Liability Issuance of preferred warrants in connection with venture loans Noncash Investing And Financing Activities, Issuance Of Preferred Warrants In Connection With Venture Loans Noncash Investing And Financing Activities, Issuance Of Preferred Warrants In Connection With Venture Loans Reclassification of deferred IPO costs from non-current assets to additional paid-in capital Noncash or Partial Noncash Reclassification Of Deferred IPO Costs From Non Current Assets To Additional Paid In Capital Reclassification of deferred IPO costs from non-current assets to additional paid-in capital. Initial public offering costs in accounts payable and accrued liabilities Initial Public Offering Costs Incurred But Not Yet Paid Initial Public Offering Costs Incurred But Not Yet Paid Accrued dividends and accretion of preferred stock to redemption value Temporary Equity, Accretion to Redemption Value Conversion of bridge loans into Series E preferred Debt Conversion, Converted Instrument, Amount Number of additional target therapy options Number Of Additional Target Therapy Options Number Of Additional Target Therapy Options Fair value of initial purchase of common stock combined with the embedded future stock Acquisition Rights Total non-contingent payments License And Option Agreement, Total Non-Contingent Payments License And Option Agreement, Total Non-Contingent Payments Consideration allocated to combined unit of accounting for License and Supply Deliverable Revenue Recognition, Multiple-deliverable Arrangements, Determination of Selling Price, Amount Discount associated with Option Deliverable License And Option Agreement, Discount Associated With Option Deliverable License And Option Agreement, Discount Associated With Option Deliverable Estimated initial term to recognize expected deliveries Revenue Recognition, Multiple-Deliverable Arrangements, Allocation to Specific Unit of Accounting, Assumptions, Initial Estimated Performance Period Revenue Recognition, Multiple-Deliverable Arrangements, Allocation to Specific Unit of Accounting, Assumptions, Initial Estimated Performance Period Revenue recognized under agreement (less than in 2017) Deferred revenue related to agreement Deferred Revenue Deferred revenue recorded as a current liability Deferred Revenue, Current Deferred revenue classified as a long term liability Deferred Revenue, Noncurrent JDRF Juvenile Diabetes Research Foundation Grant Agreement [Member] Represents information pertaining to Juvenile Diabetes research foundation grant agreement. Project [Axis] Project [Axis] Project [Domain] Project [Domain] Second Contract Second Contract [Member] Second Contract [Member] Aggregate amount of grant Grants From Entities Amount Of Grant Award Represents information pertaining to aggregate amount of grant. Revenue recognized Revenue from Grants Schedule of Weighted Average Assumptions Used for Stock Option Grants Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summary of Activity Under the 2008 Plan and the 2016 Plan Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Assumptions Used to Estimate the Fair Value of Purchase Rights Granted Under the ESPP Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Schedule of Authorized Shares of Common Stock for Future Issuance Schedule of Stock by Class [Table Text Block] Document and Entity Information 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 Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Entity Voluntary Filers Entity Voluntary Filers Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Entity Current Reporting Status Entity Current Reporting Status Skolkovo Russia Vased Development Fund Of New Technologies Development And Commercialization Center Grant Agreement [Member] Represents information pertaining to russi vased development fund of new technologies development and commercialization center grant agreement. Percentage of estimated total cost of research plan Percentage Of Estimated Cost Of Research Plan Represents information pertaining to percentage of estimated cost of research plan. Remaining percentage of estimated costs to be contributed by the Company Remaining Percentage Contributed By The Entity Represents information pertaining to remaining percentage contributed by the entity. Payments received Period after completion of project when Company may be required to reimburse the funds received Period To Audit Expenditure Incurred Represents information pertaining to period to audit expenditure incurred. Temporary Equity Disclosure [Abstract] Preferred Stock Temporary Equity Disclosure [Text Block] The entire disclosure for temporary equity. Tax at U.S. statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent State taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Permanent items Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Research tax credits/other Effective Income Tax Rate Reconciliation, Tax Credit, Percent Change in enacted rates Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Valuation allowance, net Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Other Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Statement of Financial Position [Abstract] Preferred stock, par value (in dollars 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, shares issued Common Stock, Shares, Issued Debt Debt Disclosure [Text Block] Principles of Consolidation Consolidation, Policy [Policy Text Block] Foreign Currency Foreign Currency Transactions and Translations Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Reverse Stock Split Stockholders' Equity, Policy [Policy Text Block] Cash Equivalents and Short Term Investments Cash Equivalents And Short Term Investments [Policy Text Block] Disclosure of accounting policy for cash equivalents and short term investments. Concentrations of Credit Risk and Off-Balance Sheet Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Debt Issuance Costs Debt, Policy [Policy Text Block] Accumulated Other Comprehensive Income (Loss) and Comprehensive Loss Comprehensive Income, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Collaboration Revenue Collaborative Arrangement, Accounting Policy [Policy Text Block] Grant Agreements Revenue Recognition Grant Revenue [Policy Text Block] Disclosure of accounting policy for revenue recognition for revenue from grants. Research and Development Costs Research and Development Expense, Policy [Policy Text Block] Clinical Trial Costs Clinical Trial Costs [Policy Text Block] Disclosure of accounting policy for clinical trial costs. Income Taxes Income Tax, Policy [Policy Text Block] Warrants Warrants [Policy Text Block] Disclosure of accounting policy for warrants. Stock-Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Net Loss Per Share Earnings Per Share, Policy [Policy Text Block] Deferred Rent Deferred Rent [Policy Text Block] Disclosure of accounting policy for deferred rent. Contingent Liabilities Contingent Liability Reserve Estimate, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Income Tax Holiday [Table] Income Tax Holiday [Table] New Accounting Pronouncement, Early Adoption [Axis] New Accounting Pronouncement, Early Adoption [Axis] New Accounting Principles, Early Adoption [Domain] New Accounting Principles, Early Adoption [Domain] New Accounting Pronouncement, Early Adoption, Effect New Accounting Pronouncement, Early Adoption, Effect [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-09 Accounting Standards Update 2016-09 [Member] Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Stock Option Tax Credit Carryforward Stock Option Tax Credit Carryforward [Member] Stock Option Tax Credit Carryforward [Member] Stock Compensation Stock Compensation Tax Credit Carryforward [Member] Stock Compensation Tax Credit Carryforward [Member] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Russia Foreign Tax Authority [Member] Domestic Tax Authority Domestic Tax Authority [Member] State and Local Jurisdiction State and Local Jurisdiction [Member] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Russian Federal Tax Service Russian Federal Tax Service [Member] Russian Federal Tax Service [Member] Income Tax Holiday [Line Items] Income Tax Holiday [Line Items] Increase in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Term of tax holiday granted to Russian subsidiary Income Tax Holiday, Term Income Tax Holiday, Term Net operating loss carryforwards Operating Loss Carryforwards Research and development tax credit carryforwards Increase in net operating losses deferred tax assets Tax Cuts and Jobs Act, reduction of deferred tax assets Tax Cuts and Jobs Act, Change in Tax Rate, Increase (Decrease) In Deferred Tax Asset Tax Cuts and Jobs Act, Change in Tax Rate, Increase (Decrease) In Deferred Tax Asset Full valuation allowance Tax Cuts and Jobs Act, Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Tax Cuts and Jobs Act, Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Unrecognized Tax Benefits Unrecognized Tax Benefits Related interest and penalties accrued Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Accrued interest related to uncertain tax positions Unrecognized Tax Benefits, Interest on Income Taxes Accrued Employee stock option grants The ESPP Employee Stock Purchase Plan2016 [Member] Represent information pertaining to the 2016 Employee Stock Purchase Plan. Fair value of common stock (in dollars per share) Common Stock, No Par Value Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected term Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Weighted-average fair value of common stock Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Fair Value Weighed-average fair value relating to the share-based payment award. MEE License Agreement With Massachusetts Eye And Ear Infirmary And Schepens Eye Research Institute Inc. [Member] Represents information pertaining to License agreement with Massachusetts Eye and Ear Infirmary and The Schepens Eye Research Institute, Inc. Minimum number of products for each target sequence Number Of Products Marketed And Sold Represents the number of products the Company has agreed to market and sell for each target sequence for which the Company exercised its option as soon as reasonably practicable. Payment under development milestone method Development Milestone Method, Amount Paid The amount of consideration paid during the period for the development milestone or milestones. Payment under sales milestone method Sales Milestone Method, Amount Paid The amount of consideration paid during the period for the sales milestone or milestones. License fees due under agreement Initial License Fee Paid Initial License Fee Paid Accrued License Fees Accrued License Fees Accrued License Fees Number of operating segments Number of Operating Segments NIH National Institutes Of Health Grant Agreement [Member] Represents information pertaining to national institutes of health grant agreement. First Grant First Grant [Member] Represents information pertaining to first grant under NIH. Second Grant Second Grant [Member] Represents information pertaining to second grant under NIH. Number of grants Number Of Grants Represents information pertaining to number of grants. Bill and Melinda Gates Foundation Bill And Melinda Gates Foundation Grant Agreement [Member] Represents information pertaining to Bill and Melinda gates foundation grant agreement. Extended research term Extended Research Term Represents information pertaining to extended research term. Revenue recognized (less than) First Acquisition Right First Acquisition Right [Member] First Acquisition Right [Member] Second Acquisition Right Second Acquisition Right [Member] Second Acquisition Right [Member] Upfront cash payment License And Option Agreement, Upfront Cash Payment License And Option Agreement, Upfront Cash Payment Aggregate additional payments due within twelve months License And Option Agreement, Aggregate Additional Payments Due Within Twelve Months Of Contract Date License And Option Agreement, Aggregate Additional Payments Due Within Twelve Months Of Contract Date Term loan number of payments Term Loan Number of Payments Term Loan Number of Payments Two payments due within 12 months of contract date License And Option Agreement, Two Payments Due Within Twelve Months Of Contract Date License And Option Agreement, Two Payments Due Within Twelve Months Of Contract Date Number of additional targets License And Option Agreement, Number Of Additional Targets For Which Other Party May Exercise Options For Additional Licenses License And Option Agreement, Number Of Additional Targets For Which Other Party May Exercise Options For Additional Licenses Variable fee the Company is eligible to receive for each additional target option elected License And Option Agreement, Variable Fee To Be Received For Each Additional Target Option Elected License And Option Agreement, Variable Fee To Be Received For Each Additional Target Option Elected Election period to exercise additional targets License And Option Agreement, Period For Other Party To Exercise Options For Additional Licenses License And Option Agreement, Period For Other Party To Exercise Options For Additional Licenses Additional development and regulatory milestone payments License And Option Agreement, Additional Development And Regulatory Milestone Payments That May Be Received License And Option Agreement, Additional Development And Regulatory Milestone Payments That May Be Received Commercialization milestone payments License And Option Agreement, Commercialization Milestone Payments That May Be Received License And Option Agreement, Commercialization Milestone Payments That May Be Received Period after first commercial sale when the Company is eligible to receive royalties Eligible Period To Receive Royalties Eligible Period To Receive Royalties Period for prior written notice to terminate license Gross proceeds Share price (in dollars per share) Aggregate price of shares Spark will have the right to purchase Stock Purchase Agreement, Authorized Amount Of Stock To Sell Stock Purchase Agreement, Authorized Amount Of Stock To Sell License and option agreement, additional sub-license payment received liability License And Option Agreement, Additional Sub-License Payment Received Liability License And Option Agreement, Additional Sub-License Payment Received Liability Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Corporate bonds Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Estimated Fair Value Available-for-sale Securities The 2008 Plan and the 2016 Plan The 2008 Plan And The 2016 Plan [Member] The 2008 Plan And The 2016 Plan [Member] Employee Awards Non‑Employee Awards Number of Options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Beginning balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Exercised (in shares) Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Ending balance (in shares) Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares Vested and expected to vest (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Weighted-average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Beginning balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forfeited (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Ending balance (in dollars per share) Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Exercise Price Vested and expected to vest (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Weighted-average remaining contractual term Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term [Abstract] n/a Outstanding, term Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Vested, term Share-based Compensation Arrangement By Share-based Payment Award, Options, Vested, Outstanding, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement By Share-based Payment Award, Options, Vested, Outstanding, Weighted Average Remaining Contractual Term Vested and expected to vest, term Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value [Abstract] n/a Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Vested Share-based Compensation Arrangement By Share-based Payment Award, Options, Vested, Outstanding, Intrinsic Value Share-based Compensation Arrangement By Share-based Payment Award, Options, Vested, Outstanding, Intrinsic Value Vested and expected to vest Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Series A Redeemable Convertible Preferred Stock Series A Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series A redeemable convertible preferred stock. Series B Redeemable Convertible Preferred Stock Series C Redeemable Convertible Preferred Stock Series C Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series C redeemable convertible preferred stock. Series SRN Redeemable Convertible Preferred Stock Series SRN Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series SRN redeemable convertible preferred stock. Series E Redeemable Convertible Preferred Stock Preferred Stock Preferred Stock [Member] Additional paid-In Capital Additional Paid-in Capital [Member] Stock option receivable Receivables from Stockholder [Member] Accumulated deficit Retained Earnings [Member] Accumulated other comprehensive loss Statement [Line Items] Statement [Line Items] Temporary equity, shares outstanding at the beginning of the period (in shares) Temporary Equity, Shares Outstanding Temporary equity, outstanding at the beginning of the period Temporary Equity, Carrying Amount, Attributable to Parent Beginning balance (in shares) Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Vesting of restricted common stock (in shares) Stock Vested During Period Share Restricted Common Stock Represents the total number of shares vested during the period as a result of Restricted Common Stock. Vesting of restricted common stock Stock Vested During Period Value Restricted Common Stock Represents the aggregate value of stock related to Restricted Common Stock vested during the period. Issuance of common stock upon exercise of options (in shares) Issuance of common stock upon exercise of options Stock Issued During Period, Value, Stock Options Exercised Stock‑based compensation expense Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Accretion of preferred stock to redemption value Accretion of preferred stock to redemption value Stockholders Equity Accretion to Redemption Value Represents the value of accretion of temporary equity to redemption value during the period. Issuance of Series E redeemable convertible preferred stock, net of issuance costs of $213,469 (in shares) Temporary Equity, Stock Issued During Period, Shares, New Issues Temporary Equity, Stock Issued During Period, Shares, New Issues Issuance of Series E redeemable convertible preferred stock, net of issuance costs of $213,469 Temporary Equity, Stock Issued During Period, Value, New Issues Issuance of common stock warrants Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants Currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Exercise of common warrants (in shares) Stock Issued During Period Shares Warrants Exercised Number of warrants exercised during the current period. Exercise of common warrants Stock Issued During The Period, Value, Warrants Exercised Stock Issued During The Period, Value, Warrants Exercised Temporary equity, conversion of convertible stock upon listing (in shares) Temporary Equity, Stock Issued During Period, Shares, Conversion Of Convertible Securities Temporary Equity, Stock Issued During Period, Shares, Conversion of Convertible Securities Conversion of convertible stock upon listing Temporary Equity, Stock Issued During Period, Value, Conversion Of Convertible Securities Temporary Equity, Stock Issued During Period, Value, Conversion Of Convertible Securities Common stock, conversion of convertible stock upon listing (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Conversion of convertible stock upon listing Stock Issued During Period, Value, Conversion of Convertible Securities Issuance of common stock, initial public offering net of issuance costs (in shares) Issuance of common stock, Initial public offering net of issuance costs Stock Issued During Period, Value, New Issues Issuance of common stock, license agreement (in shares) Stock Issued During Period, Shares, Purchase of Assets Issuance of common stock, Private placement net of issuance costs (in shares) Stock Issued During Period Value Conversion Preferred Stock Warrants, Shares Stock Issued During Period Value Conversion Preferred Stock Warrants, Shares Issuance of common stock, Private placement net of issuance costs Stock Issued During Period Value Conversion Preferred Stock Warrants The gross value of stock issued during the period upon the conversion of preferred stock warrants. Issuance of common stock under Employee Stock Purchase Plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Issuance of common stock under Employee Stock Purchase Plan Stock Issued During Period, Value, Employee Stock Purchase Plan Unrealized gains (losses) on securities Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Temporary equity, shares outstanding at the end of the period (in shares) Temporary equity, outstanding at the end of the period Ending balance (in shares) Statement of Comprehensive Income [Abstract] Operating expenses: Cost of Revenue [Abstract] Research and development Research and Development Expense General and administrative General and Administrative Expense Total operating expenses Loss from operations Operating Income (Loss) Investment income Investment Income, Net Loss on extinguishment of debt Foreign currency transaction gain (loss), net Foreign Currency Transaction Gain (Loss), before Tax Interest expense Other income (expense), net Other Nonoperating Income (Expense) Net loss Other comprehensive loss: Other Comprehensive Income (Loss), Tax [Abstract] Foreign currency translation adjustment Unrealized gain (loss) on securities Total comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Net loss attributable to common stockholders Net loss per share attributable to common stockholders: Earnings Per Share, Basic and Diluted [Abstract] Weighted average common shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic and diluted (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted Payroll and employee related expenses Employee-related Liabilities, Current Current portion of deferred rent and lease incentive Collaboration and licensing Accrued Collaboration and Licensing Accrued Collaboration and Licensing Accrued patent fees Accrued Patent Fees Current Carrying value as of the balance sheet date of patent fees. Accrued external research and development costs Accrued Research And Development Costs Current Carrying value as of the balance sheet date of research and development costs. Accrued professional and consulting services Accrued Audit Fees, Current Accrued Audit Fees, Current Accrued grant refund Accrued Grant Refund, Current Accrued Grant Refund, Current Accrued interest Interest Payable, Current Other Other Accrued Liabilities, Current Accrued expenses Accrued Liabilities, Current Issuance of redeemable convertible preferred stock, issuance costs Furniture Equipment Equipment [Member] Computer and office equipment Estimated useful life Property, Plant and Equipment, Useful Life Upfront payment for initial indication Initial Payment For First Indication Represents information pertaining to initial payment for first indication. Additional payment for initial indication Additional Payment For Preclinical Research For Each Indication Represents information pertaining to additional payment for preclinical research for each indication. Additional payments received upon exercise of option Proceeds From Counterparty Exercise Of Option For Additional Indications Proceeds From Counterparty Exercise Of Option For Additional Indications Additional payment upon attaining first milestone for celiac disease indication Initial period to complete research obligations Initial Period To Complete Research Obligations Initial Period To Complete Research Obligations Revenue recognized ESPP Number of offering periods under the ESPP Number Of Offering Periods Number Of Offering Periods Term of each offering period Offering Period Offering Period Eligible compensation withheld for use (up to) (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate Purchase price of shares (as a percent) Common stock authorized and reserved for future issuance (in shares) Number of shares of common stock outstanding (as a percent) Shares of common stock issued to employees under the ESPP (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Stock-based compensation expense (less than in 2017) Numerator: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Less: accretion on preferred stock Denominator: Weighted‑average common shares outstanding—basic and diluted (in shares) Concentration Risk [Table] Concentration Risk [Table] Russian subsidiary Currency [Axis] Currency [Axis] All Currencies [Domain] All Currencies [Domain] U.S. dollars United States of America, Dollars Concentration Risk [Line Items] Concentration Risk [Line Items] Cash maintained in Russian bank accounts Cash 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 [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock options to purchase common stock Redeemable convertible preferred stock Redeemable Convertible Preferred Stock [Member] Redeemable convertible preferred stock warrants Redeemable Convertible Preferred Stock Warrants [Member] Redeemable Convertible Preferred Stock Warrants [Member] Potential common shares Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Total (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Short-term deposits and investments Short-term Investments Restricted cash Restricted Cash and Cash Equivalents, 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 Restricted cash and other deposits Restricted Cash and Investments, Noncurrent Other assets Other Assets, Noncurrent Total assets Assets Liabilities and stockholders’ equity Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued expenses Loans payable, current portion Loans Payable, Current Deferred revenue, current portion Total current liabilities Liabilities, Current Non‑current liabilities: Other Liabilities, Noncurrent [Abstract] Deferred rent and lease incentive Deferred Rent Credit, Noncurrent Loans payable, net of current portion Loans Payable, Noncurrent Deferred revenue, net of current portion Other long‑term liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Commitments and contingencies (Notes 8 and 13) Commitments and Contingencies Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively Preferred Stock, Value, Issued Common stock, $0.0001 par value; 200,000,000 shares authorized; 22,343,254 and 18,438,742 shares issued and outstanding as of December 31, 2017 and December 31, 2016, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Receivable from stock option exercises Receivable from Shareholders or Affiliates for Issuance of Capital Stock Accumulated deficit Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders’ equity Total liabilities and stockholders’ equity Liabilities and Equity Schedule of Future Minimum Payments on the Term Loans Schedule of Maturities of Long-term Debt [Table Text Block] Defined Contribution Plan [Table] Defined Contribution Plan [Table] Retirement Plan Name [Axis] Retirement Plan Name [Axis] Retirement Plan Name [Domain] Retirement Plan Name [Domain] 401(k) Plan 401(k) Plan [Member] 401(k) Plan [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Defined-contribution savings plan Other Postretirement Benefits Plan [Member] Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] Vesting period Defined Contribution Plan Employers Matching Contribution Vesting Period Period which an employee's right to exercise a plan is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Employer contribution made Defined Contribution Plan, Cost Schedule of Future Minimum Lease Payments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Authorized shares of Preferred Stock (in shares) Temporary Equity, Shares Authorized Preferred Stock, par value (in dollars per share) Temporary Equity, Par or Stated Value Per Share Temporary Equity, by Class of Stock [Table] Temporary Equity, by Class of Stock [Table] Series D Preferred Stock [Member] Series D Preferred Stock [Member] Series E Preferred Stock [Member] Series E Preferred Stock [Member] Stock Conversion Description [Axis] Stock Conversion Description [Axis] Conversion of Stock, Name [Domain] Conversion of Stock, Name [Domain] Preferred stock automatically converted into common stock upon the closing of the IPO Preferred Stock Automatically Converted Into Common Stock Upon Closing Of Initial Public Offering [Member] Preferred Stock Automatically Converted Into Common Stock Upon Closing Of Initial Public Offering [Member] Preferred stock Temporary Equity [Line Items] Convertible preferred stock automatically converted into common stock (in shares) Conversion of Stock, Shares Converted Property and Equipment Property, Plant and Equipment Disclosure [Text Block] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Difference between Revenue Guidance in Effect before and after Topic 606 Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Accounting Standards Update 2015-01 Accounting Standards Update 2015-01 [Member] Accounting Standards Update 2016-09, Excess Tax Benefit Component Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member] Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member] Accounting Standards Update 2016-18 Accounting Standards Update 2016-18 [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Restatement Adjustment Restatement Adjustment [Member] Scenario, Forecast Scenario, Forecast [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Adjustment to the consolidated statements of operations Increase in valuation allowance Operating Loss Carryforwards, Valuation Allowance Cash and cash equivalents at beginning of period, presented upon implementation of ASU 2016-18 Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Stock Incentive Plans Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Minpromtorg Russian Ministry Of Industry And Trade Grant Agreement [Member] Represents information pertaining to Russian Ministry of industry and trade grant agreement. Contract awarded Repayment of funds previously received Repayment of Grant funding received The cash outflow of grant funding received Penalty fee (as a percent) Penalty Fee,Percentage Of Contract Value Represents information pertaining to penalty fee as percent of contract value. Penalty fee Penalty Fee Amount Represents information pertaining to penalty fee. Period to audit expenditure incurred Restricted shares Restricted Stock [Member]