Inventory Disclosure [Abstract] Raw materials Inventory, Raw Materials, Net of Reserves Finished goods Inventory, Work in Process, Net of Reserves Total inventory Inventory, Net Write-off of inventory Inventory Write-down Document And Entity Information [Abstract] Document and Entity Information [Abstract] 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 Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Accounting Policies [Abstract] Revenue Revenue Recognition, Policy [Policy Text Block] Revenue, Discounts and Refunds Revenue Recognition, Revenue Reductions [Policy Text Block] Accounts receivable Receivables, Policy [Policy Text Block] Allowance for doubtful accounts Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Advertising expense Advertising Costs, Policy [Policy Text Block] Shipping and handling costs Shipping and Handling Cost, Policy [Policy Text Block] Basis of presentation Basis of Accounting, Policy [Policy Text Block] Use of estimates Use of Estimates, Policy [Policy Text Block] Principles of consolidation Consolidation, Policy [Policy Text Block] Concentration of risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Recent accounting pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Fair value measurements Fair Value Measurement, Policy [Policy Text Block] Cash equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Marketable securities Marketable Securities, Policy [Policy Text Block] Earnings Per Share [Abstract] Net loss per share Earnings Per Share [Text Block] Cash and Cash Equivalents [Abstract] Schedule of Marketable Securities Available-for-sale Securities [Table Text Block] 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] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Flex Pharma, Inc. 2014 Equity Incentive Plan Flex Pharma, Inc. 2014 Equity Incentive Plan [Member] Flex Pharma, Inc. 2014 Equity Incentive Plan [Member] 2015 Equity Incentive Plan Equity Incentive Plan 2015 [Member] Equity Incentive Plan 2015 [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Employee stock option Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Shares remaining available for grant of stock awards Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Stock options, vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Stock options, contractual term Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Unrecognized compensation cost Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options Unrecognized compensation cost, recognition period (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Statement of Cash Flows [Abstract] Operating activities Net Cash Provided by (Used in) Operating Activities [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 expense Depreciation Stock-based compensation expense Share-based Compensation Amortization and accretion on investments Investment Income, Net, Amortization of Discount and Premium Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Restricted cash Increase (Decrease) in Restricted Cash for Operating Activities Accounts receivable Increase (Decrease) in Accounts Receivable Inventory Increase (Decrease) in Inventories Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Other assets Increase (Decrease) in Other Noncurrent Assets Accounts payable Increase (Decrease) in Accounts Payable Accrued expenses and other current liabilities Increase (Decrease) in Accrued Liabilities Deferred revenue Increase (Decrease) in Deferred Revenue Deferred rent Increase (Decrease) in Deferred Liabilities Other long term liabilities Increase (Decrease) in Other Noncurrent Liabilities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of marketable securities Payments to Acquire Marketable Securities Proceeds from maturities and sales of marketable securities Proceeds from Sale and Maturity of Marketable Securities Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Proceeds from sales 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 Financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from exercise of common stock Proceeds from Stock Options Exercised Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net decrease in cash and cash equivalents Cash, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash Cash and cash equivalents at end of period Supplemental cash flow information Supplemental Cash Flow Information [Abstract] Property and equipment purchases included in accounts payable at September 30, 2017 Capital Expenditures Incurred but Not yet Paid Property and equipment purchases included in accounts payable and accrued expenses at December 31, 2016 and 2015 Property And Equipment Purchases In Accrued Expense Property and Equipment Purchases In Accrued Expense Inventory purchases included in accrued expenses at September 30, 2016 Inventory Purchases in Accounts Payable and Accrued Expense Inventory Purchases in Accounts Payable and Accrued Expense Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] 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] 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] U.S. government agency securities US Government Agencies Debt Securities [Member] Commercial paper Commercial Paper [Member] Corporate debt securities Corporate Debt 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] Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Marketable securities: Marketable Securities [Abstract] Fair Value Available-for-sale Securities Total assets Assets, Fair Value Disclosure Equity [Abstract] Restricted common stock activity Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Summary of stock option activity Share-based Compensation, Stock Options, Activity [Table Text Block] Summary of stock-based compensation expense Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Common stock Stockholders' Equity Note Disclosure [Text Block] Statement of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Marketable securities Marketable Securities, Current Accounts receivable Accounts Receivable, Net, Current Inventory 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 Other assets Other Assets, Noncurrent Restricted cash Restricted Cash and Cash Equivalents, Noncurrent Total assets Assets Liabilities and stockholders' equity Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued expenses and other current liabilities Accrued Expenses And Other Current Liabilities Accrued Expenses And Other Current Liabilities Deferred revenue Deferred Revenue, Current Deferred rent, current portion Deferred Rent Credit, Current Total current liabilities Liabilities, Current Deferred rent, net of current portion Deferred Rent Credit, Noncurrent Total liabilities Liabilities Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock, $0.0001 par value; 10,000,000 shares authorized at September 30, 2017 and December 31, 2016; none issued or outstanding at September 30, 2017 and December 31, 2016 Preferred Stock, Value, Issued Common stock, $0.0001 par value; 100,000,000 shares authorized at September 30, 2017 and December 31, 2016; 17,971,816 and 17,970,590 shares issued at September 30, 2017 and December 31, 2016, and 17,541,377 and 16,773,798 shares outstanding at September 30, 2017 and December 31, 2016, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated deficit Retained Earnings (Accumulated Deficit) Total stockholders' equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders' equity Liabilities and Equity Segment Reporting [Abstract] Number of reportable segments Number of Reportable Segments Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate Corporate, Non-Segment [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Consumer Operations Consumer Operations [Member] Consumer Operations [Member] Drug Development Drug Development [Member] Drug Development [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Total revenue Revenue, Net Interest income, net Interest Income, Operating Loss from operations Operating Income (Loss) Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] 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 Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Number of debt securities held Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Aggregate fair value of debt securities in an unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value 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] Options to purchase common stock Unvested restricted common stock Restricted Stock [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive securities excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Inventory Inventory Disclosure [Text Block] Restricted stock Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Vests upon issuance Share-based Compensation Award, Tranche One [Member] Vests ratably over four years Share-based Compensation Award, Tranche Two [Member] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Non-employee Consultants and Advisers Non-employee Consultants and Advisers [Member] Non-employee Consultants and Advisers [Member] Restricted common stock, shares sold (in shares) Stock Issued During Period, Shares, New Issues Restricted common stock, price per share (in usd per share) Sale of Stock, Price Per Share Proceeds from sale of restricted common stock to founders Proceeds From Sale Of Restricted Common Stock Proceeds From Sale Of Restricted Common Stock Restricted common stock, percent vested Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Restricted common stock, vesting period (in years) Restricted common stock, repurchase period (in days) Stock Repurchase Program, Period in Force Restricted common stock, repurchase price (in usd per share) Treasury Stock Acquired, Average Cost Per Share Restricted common stock, shares outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Organization, Consolidation and Presentation of Financial Statements [Abstract] Retained earnings (accumulated deficit) Cash, cash equivalents, and marketable securities Cash, Cash Equivalents, and Short-term Investments 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] Beginning balance, unvested, number of shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Issued, number of shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested, number of shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited, number of shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Ending balance, unvested, number of shares 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] Beginning balance, weighted average grant date fair value (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Issued, weighted average grant date fair value (in usd 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, weighted average grant date fair value (in usd 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, weighted average grant date fair value (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Ending balance, weighted average grant date fair value (in usd per share) Organization and operations Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Payables and Accruals [Abstract] Schedule of accrued expenses Schedule of Accrued Liabilities [Table Text Block] Schedule of other current liabilities Other Current Liabilities [Table Text Block] Income Tax Disclosure [Abstract] Income taxes Income Tax Disclosure [Text Block] Schedule of antidilutive securities excluded from computation of earnings per share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Inventory, Net Schedule of Inventory, Current [Table Text Block] Schedule of Information for the Company's Operating Segments Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Summary of Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Accrued expenses and other current liabilities Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Fair value measurements Fair Value Disclosures [Text Block] Cash equivalents and marketable securities Cash, Cash Equivalents, and Marketable Securities [Text Block] Refund period from day of shipment (in days) Revenue Recognition, Refund Period Revenue Recognition, Refund Period Advertising expense Advertising Expense Shipping and handling costs Shipping, Handling and Transportation Costs New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [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, Forfeiture Rate Component Accounting Standards Update 2016-09, Forfeiture Rate Component [Member] Accounting Standards Update 2016-09, Forfeiture Rate Component [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] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Cumulative effect adjustment Cumulative Effect of New Accounting Principle in Period of Adoption Deferred tax assets Deferred Tax Assets, Net Research and development costs Accrued Research And Development Expense, Current Accrued Research and Development Expense, Current Payroll and employee-related costs Employee-related Liabilities, Current Professional fees Accrued Professional Fees, Current Consumer product-related costs Accrued Marketing Costs, Current Total Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Shares outstanding, Beginning Balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Shares granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Shares exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Shares canceled or forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Shares outstanding, Ending Balance Shares exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Shares vested or expected to vest 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] Shares outstanding, weighted-average exercise price, Beginning Balance (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Shares granted, weighted-average exercise price (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Shares exercised, weighted-average exercise price (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Shares canceled or forfeited, weighted-average exercise price (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Shares outstanding, weighted-average exercise price, Ending Balance (in usd per share) Shares exercisable, weighted-average exercise price (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Shares vested or expected to vest, weighted-average exercise price (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Outstanding, weighted-average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Exercisable, weighted-average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Vested or expected to vest, weighted-average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Outstanding, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Exercisable, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Vested or expected to vest, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Stock-based compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Statement of Comprehensive Income [Abstract] Other comprehensive gain (loss): Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized gain (loss) on available-for-sale securities Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent 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 Expense [Member] Selling, general and administrative General and Administrative Expense [Member] Employee Service Share-Based Compensation Allocation of Recognized Period Costs [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Stock-based compensation expense Allocated Share-based Compensation Expense Income tax provision (benefit) Income Tax Expense (Benefit) Segment Information Segment Reporting Disclosure [Text Block] Income Statement [Abstract] Net product revenue Sales Revenue, Goods, Net Other revenue Other Revenue, Net Total revenue Costs and expenses: Operating Expenses [Abstract] Cost of product revenue Cost of Goods Sold Research and development Research and Development Expense Selling, general and administrative General and Administrative Expense Total costs and expenses Operating Expenses Loss from operations Net loss Net loss attributable to common stockholders Net Income (Loss) Available to Common Stockholders, Basic Net loss per share attributable to common stockholders - basic and diluted (in usd per share) Earnings Per Share, Basic and Diluted Weighted-average number of common shares outstanding — basic and diluted (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted Summary of significant accounting policies and recent accounting pronouncements Significant Accounting Policies [Text Block]