Document and Entity Information Document Information [Table] Document Information [Line Items] Document and Entity Information Entity Registrant Name Document Type Document Period End Date Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Interactive Data Current Entity Filer Category Entity Small Business Entity Emerging Growth Company Entity Ex Transition Period Entity Shell Company Entity Public Float Entity Common Stock, Shares Outstanding Entity Central Index Key Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Period Focus Amendment Flag Consolidated and Combined Balance Sheets Assets [Abstract] ASSETS Assets, Current [Abstract] Current assets: Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Accounts Receivable, Related Parties, Current Related party accounts receivable Prepaid Expense, Current Prepaid expenses Other Assets, Current Other current assets Assets, Current Total current assets Restricted Cash and Cash Equivalents, Noncurrent Restricted cash, net of current portion Restricted cash in non-current assets Property, Plant and Equipment, Net Property and equipment, net Property and equipment, net Operating Lease, Right-of-Use Asset Operating lease right-of-use asset Right-of-use asset Other Assets, Noncurrent Other assets Assets Total assets Liabilities and Equity [Abstract] LIABILITIES AND STOCKHOLDERS' EQUITY (DEFICIT) Liabilities, Current [Abstract] Current liabilities: Accounts Payable, Current Accounts payable Accounts Payable, Related Parties, Current Related party accounts payable Carrying value as of the balance sheet date of obligations incurred through that date and payable for research and development. Used to reflect the current portion of liabilities. Accrued Research And Development Current Accrued research and development costs Amount of accrued expenses and other liabilities current. Accrued Expenses and Other Liabilities Current Accrued expenses and other current liabilities Total Operating Lease, Liability, Current Current portion of operating lease liabilities Less: current portion of operating lease liabilities Liabilities, Current Total current liabilities Operating Lease, Liability, Noncurrent Operating lease liabilities, net of current portion Operating lease liabilities, net of current portion Noncurrent lease liability Commitments and Contingencies. Commitments and contingencies Stockholders' Equity Attributable to Parent [Abstract] Stockholders' equity (deficit) Common Stock, Value, Issued Common stock, no par value, 400,000,000 shares authorized and 27,598,133 issued and outstanding at December 31, 2019 and no shares issued or outstanding at December 31, 2018 Retained Earnings (Accumulated Deficit) Accumulated deficit Net amount of parent investment. Net Parent Investment Net parent investment Additional Paid in Capital, Common Stock Paid-in capital Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income (loss) Stockholders' Equity Attributable to Parent Ending balance Beginning balance Total stockholders' equity (deficit) Liabilities and Equity Total liabilities and stockholders' equity (deficit) Common stock, par value (in dollars per share) Common stock, shares authorized Common stock, shares issued Common stock, shares outstanding Ending balance (in shares) Beginning balance (in shares) Consolidated and Combined Statements of Operations and Comprehensive Loss Revenue from Contract with Customer, Excluding Assessed Tax Revenue from related party Operating Expenses [Abstract] Cost and expenses: Research and Development Expense Research and development General and Administrative Expense General and administrative Operating Expenses Operating expense Total cost and expenses Operating Income (Loss) Loss from operations Investment Income, Nonoperating Interest and other income Net Income (Loss) Attributable to Parent Net loss Net loss Loss per share Net loss per share: Earnings Per Share, Basic and Diluted Basic and diluted net loss per share (in dollars per share) Net loss per share - basic and diluted Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract] Weighted average shares used in calculating: Weighted Average Number of Shares Outstanding, Basic and Diluted Basic and diluted net loss per share (in shares) Number of common shares used in net loss per share - basic and diluted (in thousands) Statement of Other Comprehensive Income [Abstract] Other comprehensive loss: Other Comprehensive Income (Loss), Net of Tax [Abstract] Other comprehensive loss: Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Foreign currency translation adjustment Other Comprehensive Income (Loss), Net of Tax Total other comprehensive loss Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive loss Consolidated and Combined Statements of Stockholders' Equity (Deficit) Statement [Table] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Change in Stockholders' Equity (Deficit) he amount of capital contributed by the parent through transfers. Contributed Capital Net transfers from Ironwood Amount of share based compensation upon separation from parent company. Share Based Compensation Upon Separation Ironwood allocation - share-based compensation Amount of adjustments made upon separation primarily related to differences between assets and liabilities transferred to Cyclerion as a result of the Separation and assets and liabilities reported in the Company's combined balance sheet. Adjustments Upon Separation Separation-related adjustments Amount of increase to additional paid-in capital (APIC) from reclassification of net parent company investment. Adjustments to Additional Paid in Capital, Reclassification of Net Parent Company Investment Reclassification of net parent company investment Number of shares of common stock distributed on prorata basis by parent company upon separation. Distribution of Common Stock Shares by Parent Company Upon Separation Distribution of common stock by Ironwood upon separation (in shares) Stock Issued During Period, Value, New Issues Issuance of common stock - private placement, net of fees Stock Issued During Period, Shares, New Issues Shares issued to accredited investors Issuance of common stock - private placement, net of fees (in shares) Value of shares issued during the period as a result of an employee stock purchase plan and exercise of stock options and Restricted Stock Units. Stock Issued During Period, Value, Exercise Of Stock Options, Restricted Stock Units And Employee Stock Purchase Plans Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan Number of shares issued during the period as a result of an employee stock purchase plan and exercise of stock options and Restricted Stock Units. Stock Issued During Period, Shares, Exercise Of Stock Options, Restricted Stock Units And Employee Stock Purchase Plans Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Issuance of common stock awards (in shares) Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan Consolidated and Combined Statements of Cash Flows Net Cash Provided by (Used in) Operating Activities [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net loss to net cash (used in) operating activities: Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Gain (Loss) on Disposition of Property Plant Equipment Loss on disposal of property and equipment Disposal loss of property and equipment, net Share-based Compensation Share-based compensation expense Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Accounts Receivable, Related Parties Related party accounts receivable Increase (Decrease) in Prepaid Expense Prepaid expenses Increase (Decrease) in Other Current Assets Other current assets Amount of increase (decrease) in operating lease assets. Increase (Decrease) in Operating Lease Assets Operating lease assets Increase (Decrease) in Other Noncurrent Assets Other assets Increase (Decrease) in Accounts Payable, Trade Accounts payable Increase (Decrease) in Accounts Payable, Related Parties Related party accounts payable The increase (decrease) during the reporting period in accrued research and development expense. Increase Decrease in Accrued Research and Development Accrued research and development costs Amount of increase (decrease) in operating lease liabilities. Increase (Decrease) in Operating Lease Liabilities Operating lease liabilities Increase (Decrease) in Other Accounts Payable and Accrued Liabilities Accrued expenses and other current liabilities Net Cash Provided by (Used in) Operating Activities Net cash (used in) operating activities Net Cash Provided by (Used in) Investing Activities [Abstract] CASH FLOWS FROM INVESTING ACTIVITIES: Payments to Acquire Property, Plant, and Equipment Purchases of property and equipment Proceeds from Sale of Property, Plant, and Equipment Proceeds from sale of property and equipment Net Cash Provided by (Used in) Investing Activities Net cash (used in) investing activities Net Cash Provided by (Used in) Financing Activities [Abstract] CASH FLOWS FROM FINANCING ACTIVITIES: Proceeds from Issuance of Private Placement Gross proceeds from issuance of shares to accredited investors Gross proceeds from private placement Payments of Stock Issuance Costs Costs associated with private placement Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options Proceeds from exercises of stock options and ESPP Proceeds from Contributed Capital Transfers from Ironwood Net Cash Provided by (Used in) Financing Activities Net cash provided by financing activities Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Effect of exchange rate changes on cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Net increase in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash, end of period Cash, cash equivalents and restricted cash, beginning of period Total cash, cash equivalents and restricted cash Supplemental Cash Flow Information [Abstract] Supplemental cash flow disclosure: Noncash Investing and Financing Items [Abstract] Non-cash investing activities Capital Expenditures Incurred but Not yet Paid Fixed asset purchases in accounts payable and accrued expenses Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Reconciliation of cash, cash equivalents and restricted cash to the condensed consolidated and combined balance sheets Restricted Cash and Cash Equivalents Restricted cash Nature of Business Business Description and Basis of Presentation [Text Block] Nature of Business Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Related Party Transactions Related Party Transactions Disclosure [Text Block] Related Party Transactions Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Fair Value of Financial Instruments Property and Equipment Property, Plant and Equipment Disclosure [Text Block] Property and Equipment Accrued Expenses and Other Current Liabilities Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Accrued Expenses and Other Current Liabilities Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Leases The entire disclosure of information about leases. Lease Disclosure [Text Block] Leases Share-based Compensation Plans Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Share-based Compensation Plans Earnings Per Share [Text Block] Loss per share Income Taxes Income Tax Disclosure [Text Block] Income Taxes Defined Contribution Plan Pension and Other Postretirement Benefits Disclosure [Text Block] Defined Contribution Plan Workforce Reduction Restructuring and Related Activities Disclosure [Text Block] Workforce Reduction Subsequent Events Subsequent Events [Text Block] Subsequent Events Basis of Accounting, Policy [Policy Text Block] Basis of Presentation Consolidation, Policy [Policy Text Block] Principles of Consolidation Segment Reporting, Policy [Policy Text Block] Segment Information Use of Estimates, Policy [Policy Text Block] Use of Estimates Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Restricted Cash Property, Plant and Equipment, Policy [Policy Text Block] Property and Equipment Fair Value of Financial Instruments, Policy [Policy Text Block] Fair Value of Investment Instruments Foreign Currency Transactions and Translations Policy [Policy Text Block] Foreign Currency Translation Adjustment Disclosure of accounting policy for related party accounts receivable. Related Party Accounts Receivable Policy [Policy Text Block] Related Party Accounts Receivable Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Impairment of Long-Lived Asset Lessee, Leases [Policy Text Block] Leases Revenue from Contract with Customer [Policy Text Block] Revenue Research and Development Expense, Policy [Policy Text Block] Research and Development Costs Selling, General and Administrative Expenses, Policy [Policy Text Block] General and Administrative Expenses Income Tax, Policy [Policy Text Block] Income taxes Disclosure of accounting policy for patent costs. Patent Costs [Policy Text Block] Patent Costs Disclosure of accounting policy for interest and other income. Interest and Other Income, Policy [Policy Text Block] Interest and Other Income Subsequent Events, Policy [Policy Text Block] Subsequent Events New Accounting Pronouncements, Policy [Policy Text Block] New Accounting Pronouncements Tabular disclosure of the useful life of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. Schedule of Property, Plant and Equipment, Useful Life [Table Text Block] Schedule of estimated useful lives of property and equipment Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule of financial assets measured at fair value on a recurring basis and indicating the level of the fair value hierarchy Property, Plant and Equipment [Table Text Block] Schedule of property and equipment, net Other Current Liabilities [Table Text Block] Schedule of accrued expenses and other current liabilities The tabular disclosure of supplemental cash flow information related to leases. Lessee, Operating Lease, Supplemental Cash Flow Information [Table Text Block] Schedule of supplemental cash flow information related to leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of future minimum lease payments under non-cancelable operating leases Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Total future minimum lease payments to be received under the sublease agreement Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Schedule of share-based compensation expense Share-based Payment Arrangement, Option, Activity [Table Text Block] Schedule of stock option activity Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of weighted-average assumptions used in estimating the fair value of the stock options Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block] Summary of stock awards containing market conditions activity Tabular disclosure of the significant assumptions used during the year to estimate the fair value of performance shares, including, but not limited to: (a) expected term of performance shares, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. Schedule Of Share-Based Payment Award, Performance Shares, Valuation Assumptions [Table Text Block] Schedule of weighted-average assumptions used in estimating the fair value of the stock awards containing market conditions Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Summary of RSU activity Nonvested Restricted Stock Shares Activity [Table Text Block] Summary of restricted stock Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of basic and diluted earnings per share Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Summary of reconciliation of income taxes computed using the U.S. federal statutory rate Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Summary of deferred tax assets (liabilities) Restructuring and Related Costs [Table Text Block] Schedule of accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce Schedule of Stock by Class [Table] Class of Stock [Line Items] n/a Nature of Operations [Abstract] Nature of Operations Entity Number of Employees Number of employees n/a Spinoff Transaction [Abstract] The Separation