Equity [Abstract] 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] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Common stock Common Stock [Member] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] At-The-Market Offering At-The-Market Offering [Member] At-The-Market Offering [Member] 2017 PIPE 2017 PIPE [Member] 2017 PIPE [Member] Springer Purchase Agreement Springer Purchase Agreement [Member] Springer Purchase Agreement [Member] Exercise of common warrants Warrant [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 Sale of stock, number of shares issued in transaction (in shares) Sale of Stock, Number of Shares Issued in Transaction Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Share price (in dollars per share) Sale of Stock, Price Per Share Stock issued (in shares) Stock Issued During Period, Shares, New Issues Exercise price (in dollars per share) Class of Warrant or Right, Exercise Price of 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. Share price (in dollars per share) Class of Warrant or Right, Issued to Purchase Common Stock Class of Warrant or Right, Issued to Purchase Common Stock Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Common stock, shares authorized (in shares) 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 Payables and Accruals [Abstract] Payroll and employee related expenses Employee-related Liabilities, Current Current portion of deferred rent and lease incentive 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)." 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 Related Party Transactions [Abstract] Related-Party Transactions Related Party Transactions Disclosure [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Year ending December 31, Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2018 (remainder) Operating Leases, Future Minimum Payments, Remainder of Fiscal Year 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 Accounting Policies [Abstract] Concentration Risk [Table] Concentration Risk [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Russian subsidiary RUSSIAN FEDERATION 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 Earnings Per Share [Abstract] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock options to purchase common stock Employee Stock Option [Member] Unvested restricted stock units Restricted Stock Units (RSUs) [Member] Stock warrants to purchase common stock 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 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] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Chief Executive Officer Chief Executive Officer [Member] 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] The 2008 Plan and the 2016 Plan The 2008 Plan And The 2016 Plan [Member] The 2008 Plan And The 2016 Plan [Member] 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. Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] 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 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Exercise price of incentive stock options (not less than) 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 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 authorized, increase (in shares) Share-Based Compensation Arrangement By Share-Based Payment Award, Number Of Shares Available For Grant, Increase (Decrease) Share-Based Compensation Arrangement By Share-Based Payment Award, Number Of Shares Available For Grant, Increase (Decrease) Common stock authorized and reserved for future issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance 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 Shares exercises in period by employees (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Aggregate intrinsic value of stock options exercised 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 Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Vested and expected to vest (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 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 Granted, net of forfeitures (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price 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] 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 stock-based compensation expense 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] Furniture and fixtures Furniture and Fixtures [Member] Laboratory and office equipment Equipment [Member] Computer equipment Computer Equipment [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Estimated useful life Property, Plant and Equipment, Useful Life Revenue from Contract with Customer [Abstract] Schedule of Impact of New Accounting Pronouncements Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Schedule of Changes in Contract Liabilities Contract with Customer, Asset and Liability [Table 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] 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) Comprehensive Income, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] 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] 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 authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Investments, Debt and Equity Securities [Abstract] Other-than-temporary impairments Other than Temporary Impairment Losses, Investments, Available-for-sale Securities ESPP Employee Stock Purchase Plan2016 [Member] Represent information pertaining to the 2016 Employee Stock Purchase Plan. 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 (not less than) (as a percent) Number of shares of common stock outstanding (as a percent) Stock-based compensation expense Accrued Expenses Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Schedule of Restricted Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Components of Accumulated Other Comprehensive Income (Loss), Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Current Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Current Short-term deposits and investments Short-term Investments 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 and other assets Restricted Cash and Investments, Noncurrent Total assets Assets Liabilities and stockholders’ equity Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued expenses Loan payable, current portion Loans Payable, Current Deferred revenue, current portion Contract with Customer, Liability, Current Total current liabilities Liabilities, Current Non‑current liabilities: Other Liabilities, Noncurrent [Abstract] Deferred rent and lease incentive Deferred Rent Credit, Noncurrent Loan payable, net of current portion Loans Payable, Noncurrent Deferred revenue, net of current portion Contract with Customer, Liability, Noncurrent Other long‑term liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Commitments and contingencies (Notes 8 and 12) 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 September 30, 2018 and December 31, 2017, respectively Preferred Stock, Value, Issued Common stock, $0.0001 par value; 200,000,000 shares authorized; 22,426,493 and 22,343,254 shares issued and outstanding as of September 30, 2018 and December 31, 2017, 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 Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders’ equity Liabilities and Equity Stock Incentive Plans Disclosure of Compensation Related Costs, Share-based Payments [Text Block] 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] Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] 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] Prepaid before the first anniversary 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 Series D Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series D redeemable convertible preferred stock. Conversion of Series E Preferred Series E Redeemable Convertible Preferred Stock [Member] Represents information pertaining to series E redeemable convertible preferred stock. Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Borrowing capacity Line of Credit Facility, Maximum 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 Warrants issued for purchase of stock (in shares) Class of Warrant or Right, Number of Securities Called by Warrants or Rights 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 Term loan facility Long-term Line of Credit Repayments of debt Repayments of Lines of Credit Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Debt issuance costs, line of credit arrangements (less than) 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 Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Remaining performance obligation Revenue, Remaining Performance Obligation, Amount Remaining performance obligation, percentage Revenue, Remaining Performance Obligation, Percentage Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] 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] 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] License and Supply Obligation License And Supply Obligation [Member] License And Supply Obligation [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Remaining performance obligation, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] 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] MIT Exclusive Patent License Agreement With Massachusetts Institute Of Technology [Member] Represents information pertaining to Exclusive patent license agreement with Massachusetts Institute of Technology. " 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 Property, Plant and Equipment [Abstract] Schedule of Property and Equipment Property, Plant and Equipment [Table Text Block] 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 Other comprehensive loss during the year Other Comprehensive Income (Loss), Net of Tax Ending balance Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net loss Net Income (Loss) Attributable to Parent Adjustments to reconcile net loss to net cash used in operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation Depreciation Amortization of premiums (accretion of discounts) on investments Accretion (Amortization) of Discounts and Premiums, Investments (Gain) loss on disposal of property and equipment Gain (Loss) on Disposition of Property Plant Equipment Non‑cash interest expense Paid-in-Kind Interest Loss on extinguishment of debt Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Prepaid expenses, deposits and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable Increase (Decrease) in Accounts Payable Deferred revenue Increase (Decrease) in Contract with Customer, Liability Accrued expenses and other liabilities Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Receipts from the maturity of short-term investments Proceeds from Maturities, Prepayments and Calls of Short-term Investments Purchases 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 provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities, 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 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 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 Net change 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 Cash, cash equivalents, and restricted cash at end of period Supplement cash flow information Supplemental Cash Flow Information [Abstract] Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activities Noncash investing 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) Debt issuance costs included in accounts payable Initial Public Offering Costs Incurred But Not Yet Paid Initial Public Offering Costs Incurred But Not Yet Paid Private placement offering costs in accounts payable and accrued liabilities Debt Conversion, Converted Instrument, Amount 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] Employee stock option grants 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 (in dollars per share) 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. Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash and Cash Equivalents, Current Restricted cash included in other assets Restricted Cash and Cash Equivalents, Noncurrent Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Grant Revenue Grant [Member] Accumulated deficit Retained Earnings [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASU 2014-09 Accounting Standards Update 2014-09 [Member] Project [Axis] Project [Axis] Project [Domain] Project [Domain] First Grant First Grant [Member] Represents information pertaining to first grant under NIH. First Acquisition Right First Acquisition Right [Member] First Acquisition Right [Member] 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. Second Acquisition Right Second Acquisition Right [Member] Second Acquisition Right [Member] NIH National Institutes Of Health Grant Agreement [Member] Represents information pertaining to national institutes of health grant agreement. NIDA National Institute On Drug Abuse [Member] National Institute On Drug Abuse [Member] Spark Letter Agreement Spark Letter Agreement [Member] Spark Letter Agreement [Member] Consideration for Promises Consideration For Promises [Member] Consideration For Promises [Member] Development Milestones Development Milestones [Member] Development Milestones [Member] Regulatory Milestones Regulatory Milestones [Member] Regulatory Milestones [Member] Commercial Milestones Commercial Milestones [Member] Commercial Milestones [Member] Discount on Option Obligation Discount On Option Obligation [Member] Discount On Option Obligation [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Number of collaboration/grant agreements that required analysis to quantify the impact of adoption Number Of Collaboration Agreements Under Analysis To Quantify Impact Of Adoption Number Of Collaboration Agreements Under Analysis To Quantify Impact Of Adoption 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 Sales milestone payments License And Option Agreement, Sales Milestone Payments That May Be Received License And Option Agreement, Sales Milestone Payments That May Be Received Number of obligations Revenue, Number Of Performance Obligations Revenue, Number Of Performance Obligations 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 Period For Prior Written Notice To Terminate License Represents information pertaining to period for prior written notice to terminate license. Sale common stock Sale of Stock, Consideration Received on Transaction 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 Deferred revenue related to agreement Contract with Customer, Liability 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 Aggregate purchase price Aggregate Purchase Price Aggregate Purchase Price 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 Number of shares authorized to be issued pursuant to the Stock Purchase Agreement (in shares) Stock Purchase Program, Number Of Shares Authorized To Be Sold Stock Purchase Program, Number Of Shares Authorized To Be Sold 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 Number of agreements combined and evaluated into a single agreement Number Of Agreements Combined Into Single Agreement For Evaluation Number Of Agreements Combined Into Single Agreement For Evaluation Fair value of initial purchase of common stock combined with the embedded future stock Acquisition Rights Stock Issued During Period, Value, Purchase of Assets Performance obligation per each option Revenue, Remaining Performance Obligation, Each Option Revenue, Remaining Performance Obligation, Each Option Incremental costs of obtaining a contract Capitalized Contract Cost, Net Revenue recognized Contract with Customer, Liability, Deferred Revenue, Revenue Recognized Contract with Customer, Liability, Deferred Revenue, Revenue Recognized 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 Aggregate amount of grant Grants From Entities Amount Of Grant Award Represents information pertaining to aggregate amount of grant. 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 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. Cumulative effect adjustment Cumulative Effect of New Accounting Principle in Period of Adoption Grants from entities, unused grant funds Grants From Entities Unused Grant Funds Grants From Entities Unused Grant Funds Overspent costs Overspent Costs Overspent Costs 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. Grant and collaboration revenue Revenue from Contract with Customer, Excluding Assessed Tax Remaining amount not recognized Grant Revenue, Available Under Grant Not Recognized Grant Revenue, Available Under Grant Not Recognized Reimbursement invoices Reimbursement Invoice Reimbursement Invoice Other liabilities Other Liabilities Debt Debt Disclosure [Text Block] Year ended December 31, Long-term Debt, Fiscal Year Maturity [Abstract] 2018 (Remainder) 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 loan payable Long-term Debt, Current Maturities Loan payable, net of current portion Long-term Debt, Excluding Current Maturities Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Founders Founder [Member] Represents information pertaining to founder member. Series D Redeemable Convertible Preferred Stock Related Party Transaction [Line Items] Related Party Transaction [Line Items] Expenses for consulting services (less than) Related Party Transaction, Expenses from Transactions with Related Party 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] 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] Schedule of Future Minimum Lease Payments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] Revenue from Contracts with Customers Revenue from Contract with Customer [Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Outstanding common stock options Class of Stock [Line Items] Class of Stock [Line Items] Total (in shares) 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 assets Restricted Cash And Other Deposits [Member] Represents inforamtion pertaining to restricted cash and other deposits member. Accrued expenses Accounts Payable and Accrued Liabilities [Member] 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 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) Rent expense Operating Leases, Rent Expense, Net Depreciation expense President President [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Employment Inducement Incentive Award Plan Employment Inducement Incentive Award Plan [Member] Employment Inducement Incentive Award Plan [Member] Net Loss Per Share Earnings Per Share [Text Block] 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 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 Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Unrealized gain on securities Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Total comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Net loss per share: Earnings Per Share, Basic and Diluted [Abstract] Net loss per share attributable to common stockholders—basic and diluted (in dollars per share) Earnings Per Share, Basic and Diluted 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 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 Income Tax Holiday [Table] Income Tax Holiday [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Russia Foreign Tax Authority [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] Current income tax expense or benefit Current Income Tax Expense (Benefit) Deferred income tax expense or benefit Deferred Income Tax Expense (Benefit) Term of tax holiday granted to Russian subsidiary Income Tax Holiday, Term Income Tax Holiday, Term 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 Laboratory equipment Laboratory Equipment [Member] Represents information pertaining to laboratory equipment. Computer equipment and software Leasehold improvements Leasehold Improvements [Member] Office equipment Office Equipment [Member] Construction in process Construction in Progress [Member] 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 Retirement Benefits [Abstract] Defined Contribution Plan Pension and Other Postretirement Benefits Disclosure [Text Block] 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] Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [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] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] U.S. government and agency securities US Treasury and Government [Member] Corporate Bonds Corporate Bond Securities [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] Average maturity, term Investments Maturity Period Represents information pertaining to US treasury obligations in investments maturity period. Fair Value Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract] Less than one year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Amortized Cost Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract] Less than one year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost 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 Exercised (in shares) Forfeited (in shares) Ending balance (in shares) Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares 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 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 Effective interest rate for debt arrangement Debt Instrument, Interest Rate, Effective Percentage 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) 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 Realized gains or losses on sale of investments Realized Investment Gains (Losses) Numerator: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Denominator: Weighted‑average common shares outstanding—basic and diluted (in shares) Schedule of Authorized Shares of Common Stock for Future Issuance Schedule of Stock by Class [Table Text Block] Contract liabilities: Change In Contract With Customer, Liability [Roll Forward] Change In Contract With Customer, Liability [Roll Forward] Deferred revenue, beginning of period Contract with Customer, Liability, Deferred Revenue Contract with Customer, Liability, Deferred Revenue Other liabilities, beginning of period Contract with Customer, Liability, Other Contract with Customer, Liability, Other Contract liabilities, beginning of period Deferred revenue, additions Contract with Customer, Liability, Deferred Revenue, Increase From Cash Receipts Contract with Customer, Liability, Deferred Revenue, Increase From Cash Receipts Other liabilities, additions Contract with Customer, Liability, Other, Increase From Cash Receipts Contract with Customer, Liability, Other, Increase From Cash Receipts Contract liabilities, additions Contract with Customer, Liability, Increase From Cash Receipts Contract with Customer, Liability, Increase From Cash Receipts Deferred revenue, deductions Other liabilities, deductions Contract with Customer, Liability, Other, Revenue Recognized Contract with Customer, Liability, Other, Revenue Recognized Contract liabilities, deductions Contract with Customer, Liability, Revenue Recognized Deferred revenue, end of period Other liabilities, end of period Contract liabilities, end of period Other liabilities, current portion Contract with Customer, Liability, Other, Current Contract with Customer, Liability, Other, Current Other liabilities, noncurrent portion Contract with Customer, Liability, Other, Noncurrent Contract with Customer, Liability, Other, Noncurrent Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Number of operating segments Number of Operating Segments Technology License Agreements Technology License Agreements [Text Block] The entire disclosure for technology license agreements. Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Shares outstanding at December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Grants in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Shares outstanding at June 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Shares outstanding at December 31, 2017 (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Grants in period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested in period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited in period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Shares outstanding at June 30, 2018 (in dollars per share) Grants in period, amount Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants In Period, Amount Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants In Period, Amount 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] Corporate bonds Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [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] Total cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Total short-term 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 Schedule of Accrued Expenses Schedule of Accrued Liabilities [Table Text Block] Available-for-Sale Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Corporate bonds Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Fair Value Debt Securities, Available-for-sale 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 Payments on the Term Loans Schedule of Maturities of Long-term Debt [Table Text Block] Accumulated deficit Russian subsidiary Unrestricted cash Unrestricted Cash [Member] Unrestricted Cash [Member] Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [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] Pro forma as if the previous accounting was in effect Calculated under Revenue Guidance in Effect before Topic 606 [Member] Adjustments due to ASU 2014-09 Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Common stock 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 Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Emerging Growth Company Entity Emerging Growth Company Entity Smaller Reporting Company Entity Small Business Entity Extended Transition Period Entity Ex Transition Period Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding