New at the Market Issuance Sales Agreement [Member] New At-The-Market Issuance Sales Agreement Represents information pertaining to new at-the-market issuance sales agreement for the sale of the entity's common shares. License Arrangement [Member] License Arrangement Represents information pertaining to license arrangement. Number of Lead Candidates Number of lead candidates Represents the number of lead candidates. Number of Lead Candidates To Be Developed Number of lead candidates to be developed Represents the number of lead candidates to be developed. Directors and their affiliates, including its largest stockholder Largest Shareholder Members Of Board Of Directors And Entities Affiliated With Directors [Member] Represents the information pertaining to directors and entities affiliated with the directors including the largest shareholder of the entity. Reserves for Uncertain Tax Positions Reserves for uncertain tax positions Represents the amount pertaining to reserves for uncertain tax positions. Patents [Policy Text Block] Patents Disclosure of accounting policy for patents. Patents [Abstract] Patents Patent Expenses Patent expenses Represents the expenses incurred to secure and defend patents during the period. Income Tax Reconciliation State and Local Operating Loss Expiration Amount State net operating loss expiration The portion of the difference, between total income tax expense or benefit as reported in the income statement for the year/accounting period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations that is attributable to state and local net operating loss expiration. Amendment Description Operating Loss Carryforwards Expiration Amount Net operating loss carryforwards expired Represents the amount of the operating loss carryforwards, before tax effects, that expired during the period. Amendment Flag M L V and Co LLC [Member] MLV & Co. LLC Represents details pertaining to MLV and Co. LLC, with whom the entity entered into an at-the-market sales agreement. Computers and Software [Member] Computers and software Long-lived, depreciable assets that are used in the creation, maintenance and utilization of information systems and purchased software applications. Debt securities due within three months of date of purchase issued by domestic or foreign corporate business, banks and other entities with a promise of repayment. Corporate Debt Securities Due within Three Months [Member] Corporate debt securities due within 3 months of date of purchase Represents the 2006 Stock Plan of the entity. Stock Plan 2006 [Member] 2006 Stock Plan Hoffman La Roche [Member] Roche Represents information pertaining to Hoffman-La Roche. Represents the General Electric Capital Corporation Term Loan in which General Electric Capital Corporation is the lender of the debt. General Electric Capital Corporation Term Loan [Member] GECC Term Loan Oxford Finance Corporation Term Loan [Member] Oxford Term Loan Represents the Oxford Finance Corporation Term Loan in which Oxford Finance Corporation is the lender of the debt. Cash and Money Market Funds [Member] Cash and money market funds Currency on hand as well as demand deposits with banks or financial institutions. It includes other kinds of accounts that have the general characteristics of demand deposits and a fund that invests in short-term money-market instruments, for example, but not limited to, commercial paper, bankers acceptances, repurchase agreements, government securities, certificates of deposit and other highly liquid securities. Document and Entity Information The carrying value as of the balance sheet date of obligations incurred and payable relating to service fees paid to contract manufacturers in connection with the production of clinical drug supplies and to contract research organizations in connection with preclinical studies and clinical trials. Used to reflect the current portion of liabilities (due within one year or within the normal operating cycle if longer). Accrued Contract Research Costs Accrued contract research costs Other accrued liabilities Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Excludes accrued contract research costs. (Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Other accrued liabilities Accrued Liabilities Current Excluding Accrued Contract Research Costs Collaboration Revenues [Abstract] Collaboration revenues: Revenues: License and Milestone Revenues License and milestone revenue Revenues earned by the entity under collaborative research and development agreements for nonrefundable, up-front license fees and milestone payments, excluding cost sharing reimbursements of research and development costs. License and milestone revenue recognized Collaborative Revenues The aggregate revenue earned under collaborative research and development agreements. Total collaboration revenues Collaboration revenues Cost Sharing Reimbursements Cost sharing reimbursements, net Cost sharing revenue, consisting of reimbursements earned by the entity for costs incurred under collaborative research and development agreements, net of any reimbursements by the entity for agreed-upon costs incurred by partners. Cost sharing revenue recognized Total revenues Total Revenues Total aggregate revenue earned under collaborative research and development agreements and grants. Current Fiscal Year End Date Award Type [Axis] Increase (Decrease) Accrued Contract and Research Costs Accrued contract research costs The increase (decrease) during the reporting period in accrued contract research costs. Proceeds from the sale of common stock to related parties Proceeds from Issuance of Common Stock to Related Parties Represents the proceeds from the issuance of common stock to related parties. The disclosure for accrued liabilities at the end of the reporting period, excluding accrued contract research costs. Other Accrued Liabilities Disclosure [Text Block] Other Accrued Liabilities License and Development Agreements Schedule of Share Based Compensation Expense Allocation of Compensation Costs and Recognized Period Costs [Table Text Block] Schedule of stock-based compensation expense Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the income statement for the period. This may include the amount of total share-based compensation cost, including the amounts attributable to each share-based compensation plan and any related tax benefits. It includes the reporting line for the costs expensed. Schedule of Other Accrued Liabilities [Table Text Block] Schedule of other accrued liabilities Tabular disclosure of the components of other accrued liabilities which excludes accrued contract research costs. Grant Revenue [Abstract] Grant Revenue Amount of Grant Awarded Amount of grant awarded The amount of grants awarded from a governmental agency. Represents the maturity period from date of purchase to classify an investment as cash and cash equivalents. Maturity period from date of purchase to classify an investment as cash and cash equivalents Maturity Period from Date of Purchase to Classify Investment as Cash and Cash Equivalents Maturity Period from Date of Purchase to Classify Investment as Marketable Securities Represents the maturity period from date of purchase to classify an investment as marketable securities. Maturity period from date of purchase to classify an investment as marketable securities Cash and Cash Equivalents and Available for Sale Securities, Gross Unrealized Gains Cash, cash equivalents and marketable securities, unrealized gains This item represents the gross unrealized gains for cash and cash equivalents securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities. Document Period End Date Cash and Cash Equivalents and Available for Sale Securities, Gross Unrealized Losses Cash, cash equivalents and marketable securities, unrealized losses This item represents the gross unrealized losses for cash and cash equivalents securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities. Proceeds from Issuance or Sale of Equity, Gross Gross proceeds from the sale of common stock Represents the cash inflow from the sale of common stock before deducting underwriters' discounts, fees and commissions, and other offering expenses. Common Stock Aggregate Offering Price Maximum aggregate offering price Represents the maximum aggregate offering price the entity may issue and sell shares of its common stock from time to time, at the entity's option, according to at-the-market issuance sales agreement with third party. Percentage of gross proceeds payable as commission Represents the percentage of gross proceeds payable as commission during the period. Percentage of Gross Proceeds Payable as Commission Increase in number of shares reserved for issuance Represents the increase in the maximum number of shares (or other type of equity) that was initially approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. Share Based Compensation Arrangement by Share Based Payment Award, Increase in Number of Shares Reserved for Issuance Share Based Compensation Arrangement by Share Based Payment Award, Percentage on Outstanding Common Stock for Computation of Annual Increase in Number of Shares Reserved for Issuance Percentage of outstanding shares of common stock used to compute annual increase in number of shares reserved for issuance Represents the percentage of outstanding shares of common stock used to compute the annual increase in the number of shares reserved for issuance. Share Based Compensation Arrangement by Share Based Payment Award, Options Outstanding Weighted Average Exercise Price [Abstract] Weighted average exercise price Share Based Compensation Arrangement by Share Based Payment Award, Options Outstanding Weighted Average Remaining Contractual Life [Abstract] Weighted average remaining contractual life Share Based Compensation Arrangement by Share Based Payment Award, Options Outstanding Aggregate Intrinsic Value [Abstract] Aggregate intrinsic value Represents the non-refundable upfront license payment received. Collaborative Arrangement, Upfront License Fee Received Non-refundable upfront license payment received Represents the initial term for research under collaborative arrangements. Collaborative Arrangement, Initial Term for Research Initial term for research Amount received related to research and development support Represents the amount received in research and development support. Collaborative Arrangement, Research and Development Support Received Arrangements and Non-arrangement Transactions [Domain] Collaborative Arrangement, Non Refundable Upfront License Fee Accelerated Recognition Accelerated recognition of remaining deferred revenue from upfront payment Represents the accelerated recognition of remaining deferred revenue from upfront payment during the period under the collaborative agreement. Collaborative Arrangement, License Revenue Recognized License revenue recognized Represents the license revenue recognized during the period under the collaborative agreement. Number of equal monthly payments of principal plus accrued interest Represents the number of equal monthly payments of principal plus accrued interest made by the entity. Debt Instrument, Number of Equal Monthly Payments of Principal Plus Accrued Interest Represents the number of equal monthly payments of principal plus accrued interest for additional borrowings that the entity may draw down in equipment financing under the loan modification agreement. Debt Instrument, Number of Equal Monthly Payments of Principal Plus Accrued Interest for Additional Borrowings Available Number of equal monthly payments of principal plus accrued interest Exit fee to be paid Represents the obligation to pay exit fee at the time of final payment of the outstanding principal balance. Debt Instrument, Exit Fee Payable at End of Term Debt Instrument, Covenant Equipment Financing Allowed without any Restriction Amount of equipment financing allowed under covenants without any restriction Represents the amount of equipment financing allowed without any restrictive covenants. Debt Instrument, Covenant Debt Assumption from Acquisitions Requiring Prior Written Consent Amount of debt assumption from acquisitions requiring prior written consent under covenants Represents the amount of debt assumption from acquisitions requiring prior written consent. Stock Issued During Period, Value, Related Party Issuance of common shares to related parties Equity impact of the value of stock issued during the period to related party by the reporting entity. Proceeds from the sale of common stock to related parties Number of shares issued to related party during the reporting period. Shares sold to related party Stock Issued During Period, Shares, Related Party Issuance of common shares to related parties (in shares) Interest Expense Recognized for Debt Financing Costs Transaction and exit fees and expenses recognized in interest expense Amount of expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Defined Contribution Plan Employers Matching Contribution Vesting Period Vesting schedule of employer's matching contribution Represents the vesting period of employer's matching contribution under the 401 (k) plan. Common Stock Voting Rights Number Number of votes per share that common stockholders are entitled to receive Represents the number of votes per share that common stockholders are entitled to receive. Issuer-Directed Registered Direct Offering Represents information pertaining to the issuer-directed registered direct offering of the common shares of the entity. Issuer Directed Registered Direct Offering [Member] Issuer-Directed Registered Direct Offering Registered Direct Offering [Member] Registered Direct Offering Represents information pertaining to the registered direct offering of the common shares of the entity. At the Market Issuance Sales Agreement [Member] Represents information pertaining to at-the-market issuance sales agreement for the sale of the entity's common shares. At-The-Market Issuance Sales Agreement Directors Including Largest Shareholder [Member] Directors, including the largest stockholder Represents information pertaining to directors including the largest shareholder of the entity. Public Offering [Member] Public Offering Represents a public offering of the entity's common shares. Public Offering Initial Closing [Member] Represents the initial closing of a public offering of the entity's common shares. Public offering, initial closing Public Offering Second Closing [Member] Represents the second closing, underwriters' option to purchase additional shares, of a public offering of the entity's common shares. Public offering, second closing, underwriters' option to purchase additional shares Directors and Entities Affiliated with Directors [Member] Directors and entities affiliated with the directors Represents information pertaining to directors and entities affiliated with the directors of the entity. Founder and Member of Board of Directors [Member] Founder and a member of the board of directors Represents information pertaining to its founder and a member of the board of directors of the entity. Stock Issued During Period Value New Issues Excluding Sales to Related Parties Issuance of common shares in equity offering, excluding to related parties, net Equity impact of the value of new stock issued during the period, excluding stock issued to related parties. Stock Issued During Period Shares New Issues Excluding Sales to Related Parties Number of new shares issued during the period, excluding sales to related parties. Issuance of common shares in equity offering, net (in shares) Offerings of Entity Stock [Table] Summarization of information disclosed concerning offerings of the entity's shares. Largest Shareholder and Member of Board of Directors [Member] Person serving on the board of directors who is the largest shareholder in the entity. Director who is largest shareholder Debt Instrument, Additional Borrowings Available Additional amount that the Company may fully utilized in equipment financing Represents the additional amount of borrowings that the entity may draw down in equipment financing under the loan modification agreement. Represents the deductions related to the exercise of common stock options included in net operating loss carryforwards. Deductions Related to Exercise of Common Stock Options Included in Net Operating Loss Carryforwards Deductions related to the exercise of common stock options included in net operating loss carryforwards Number of Non Cancelable and Renewable Operating Leases Represents the number of non-cancelable and renewable operating leases. Number of non-cancelable and renewable operating leases Stock Issued During Period Warrants Issues Warrants issued (in shares) Number of warrants issued during the period. Marketable securities, Unrealized gains Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. Available for Sale Securities Accumulated Gross Unrealized Gain Before Tax Available for Sale Securities Accumulated Gross Unrealized Gain Before Tax Marketable securities, Unrealized losses Available for Sale Securities Accumulated Gross Unrealized Loss Before Tax Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. Available for Sale Securities Accumulated Gross Unrealized Loss Before Tax Employee stock options An arrangement whereby an employee or member of the Board of Directors 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. Employee and Directors Stock Options [Member] Common stock options Stock option Co-Development Agreement Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Filer Category Entity Public Float Entity Registrant Name Entity Central Index Key Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Period Focus Document Type Summary of Significant Accounting Policies Accounts payable Accounts Payable, Current Professional fees Accrued Professional Fees, Current Less accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss) [Member] Additional paid-in-capital Additional Paid in Capital, Common Stock Additional paid-in Capital Additional Paid-in Capital [Member] Compensation expense related to stock options for services Adjustments to Additional Paid in Capital, Share-based Compensation, Stock Options, Requisite Service Period Recognition 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] Stock-based compensation expense Allocated Share-based Compensation Expense Antidilutive Securities [Axis] Anti-dilutive securities Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities, Name [Domain] Outstanding securities not included in the computation of diluted net income (loss) per common share as their inclusion would be anti-dilutive (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Impairment of Long-Lived Assets Asset Impairment Charges [Abstract] Total assets Assets Current assets: Assets, Current [Abstract] Assets Assets [Abstract] Total current assets Assets, Current Equipment under capital lease Assets Held under Capital Leases [Member] Marketable securities Available-for-sale Securities Marketable securities Available-for-sale Securities, Current Counterparty Name [Axis] 2015 Capital Leases, Future Minimum Payments Due in Two Years Total minimum payments Capital Leases, Future Minimum Payments Due Less: amount representing interest Capital Leases, Future Minimum Payments, Interest Included in Payments Current portion of capital lease obligations Less current portions of obligations Capital Lease Obligations, Current Present value of minimum payments Capital Lease Obligations Capital lease obligations, net of current portion Long term obligation Capital Lease Obligations, Noncurrent 2016 Capital Leases, Future Minimum Payments Due in Three Years Capital leases Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract] Assets acquired under capital lease Capital Lease Obligations Incurred 2014 Capital Leases, Future Minimum Payments Due, Next Twelve Months Cost Reported Value Measurement [Member] Cash and Cash Equivalents [Axis] Cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash and Cash Equivalents, at Carrying Value Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Cash, Cash Equivalents and Marketable Securities Cash, Cash Equivalents, and Marketable Securities [Text Block] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Cash, Cash Equivalents and Marketable Securities Total cash, cash equivalents and marketable securities Cash, cash equivalents and marketable securities Cash, Cash Equivalents, and Short-term Investments At-The-Market Issuance Sales Agreement License and Development Agreements Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative agreement Collaborative Arrangement [Member] Co-Development Agreement Collaborative Arrangement Disclosure [Text Block] Commitments and Contingencies. Commitments and contingencies (Note 11) Commitments and Contingencies Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock Common Stock [Member] Common stock, par value $0.0001 per share Authorized: 200,000,000 shares at March 31, 2014 and December 31, 2013; 87,593,991 and 85,232,506 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively Common Stock, Value, Issued Common stock, shares issued Balance (in shares) Balance (in shares) Common Stock, Shares, Issued Common stock, Authorized shares Common Stock, Shares Authorized Common stock, shares outstanding Common Stock, Shares, Outstanding Common Stock Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract] Retirement Plan Significant portions of deferred tax assets and deferred tax liabilities Components of Deferred Tax Assets and Liabilities [Abstract] Comprehensive Loss Comprehensive Income, Policy [Policy Text Block] Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Principles of Consolidation Consolidation, Policy [Policy Text Block] Schedule of future minimum payments, excluding operating costs and taxes, under the Company's capital and non-cancellable operating leases Contractual Obligation, Fiscal Year Maturity Schedule [Table Text Block] Corporate debt securities due within 1 year of date of purchase Corporate Debt Securities [Member] Operating expenses: Costs and Expenses [Abstract] Term Loans Commitments and Contingencies Debt Instrument [Line Items] Schedule of Long-term Debt Instruments [Table] Term Loans Term Loans Debt Disclosure [Text Block] Legal fees and expenses paid Debt Issuance Cost Annual interest rate on term loan (as a percent) Debt Instrument, Interest Rate, Stated Percentage Depreciation and amortization Deferred Tax Assets, Property, Plant and Equipment Deferred tax assets: Deferred Tax Assets, Net of Valuation Allowance [Abstract] Deferred tax assets Deferred Tax Assets, Gross Other Deferred Tax Assets, Other Federal and state research and development credits Deferred Tax Assets, Tax Credit Carryforwards, Research Deferred compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Federal and state net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Less valuation allowance Deferred Tax Assets, Valuation Allowance Matching contribution percentage Defined Benefit Plan Disclosure [Line Items] Percentage of employee's salary that is subject to Company matching Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Company contributions Defined Contribution Plan, Cost Recognized Depreciation and amortization Depreciation, Depletion and Amortization Director Director [Member] Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Stock-Based Compensation Basic and diluted net loss per common share (in dollars per share) Net loss per common share-basic and diluted (in dollars per share) Earnings Per Share, Basic and Diluted Basic and Diluted Loss Per Common Share Earnings Per Share, Policy [Policy Text Block] Net loss per common share: Basic and Diluted Earnings (Loss) Per Common Share Earnings Per Share [Abstract] Compensation and benefits Employee-related Liabilities, Current Unrecognized stock compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average remaining period Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Total cash received from stock option exercises Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options Laboratory equipment Equipment [Member] Equity Component [Domain] Fair value Estimate of Fair Value Measurement [Member] Fair Value, Hierarchy [Axis] Measurement Basis [Axis] Fair Value Hierarchy [Domain] Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Fair Value Measurement [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Furniture and fixtures Furniture and Fixtures [Member] General and administrative General and Administrative Expense General and administrative General and Administrative Expense [Member] Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Impairment of assets Impairment of Long-Lived Assets Held-for-use Condensed Consolidated Statements of Operations Income Statement Location [Axis] Income Taxes Income Tax Authority [Domain] Income Tax Authority [Axis] Income Taxes Income Tax Disclosure [Text Block] Income Statement Location [Domain] Increase in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount State tax rate change Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate Effective Income Tax Rate Reconciliation, Amount [Abstract] Stock-based compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount Tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Amount Income Taxes Income Tax Uncertainties [Abstract] Benefit at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Income Taxes Income Tax, Policy [Policy Text Block] State taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Foreign rate differential Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount Accounts payable Increase (Decrease) in Accounts Payable, Trade Other assets Increase (Decrease) in Other Noncurrent Assets Deferred collaboration revenue Increase (Decrease) in Deferred Revenue Other accrued liabilities Increase (Decrease) in Other Accrued Liabilities Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Collaboration receivable Increase (Decrease) in Receivables Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Interest expense, net Interest Income (Expense), Nonoperating, Net Interest expense recognized Interest Expense, Debt Cash paid for interest Interest Paid Federal Internal Revenue Service (IRS) [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Leasehold improvements Leasehold Improvements [Member] Total current liabilities Liabilities, Current Total liabilities and stockholders' equity Liabilities and Equity Total long-term liabilities Liabilities, Noncurrent Current liabilities: Liabilities, Current [Abstract] Total liabilities Liabilities Long-term liabilities: Liabilities, Noncurrent [Abstract] Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] 2015 Long-term Debt, Maturities, Repayments of Principal in Year Two 2016 Long-term Debt, Maturities, Repayments of Principal in Year Three 2014 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Marketable Securities Marketable Securities, Policy [Policy Text Block] Future principal payments under the GECC and Oxford Term Loans Maturities of Long-term Debt [Abstract] Maximum Maximum [Member] Minimum Minimum [Member] Nature of Business Nature of Operations [Text Block] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net increase (decrease) in cash and cash equivalents Net Cash Provided by (Used in) Continuing Operations Net loss Net income (loss) for basic and diluted calculations Net loss Net loss Net Income (Loss) Available to Common Stockholders, Basic Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Officer Officer [Member] Operating leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2017 Operating Leases, Future Minimum Payments, Due in Four Years Total operating expenses Operating Expenses 2016 Operating Leases, Future Minimum Payments, Due in Three Years Rent expense under operating leases Operating Leases, Rent Expense, Net 2014 Operating Leases, Future Minimum Payments Due, Next Twelve Months Loss from operations Loss from operations Operating Income (Loss) Operating Loss Carryforwards [Table] Income Taxes Operating Loss Carryforwards [Line Items] 2015 Operating Leases, Future Minimum Payments, Due in Two Years Total minimum payments Operating Leases, Future Minimum Payments Due Net operating loss carryforwards Operating Loss Carryforwards Nature of Business Summary of Significant Accounting Policies Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Other assets Other Assets, Noncurrent Other (expense) income: Other Other Accrued Liabilities, Current Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized (loss) gain on available-for-sale securities Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Other Accrued Liabilities Purchase and retirement of common stock from an officer Payments for Repurchase of Common Stock Purchases of marketable securities Payments to Acquire Available-for-sale Securities Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Retirement Plan Pension and Other Postretirement Benefits Disclosure [Text Block] Plan Name [Domain] Plan Name [Axis] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, par value $0.0001 per share Authorized: 5,000,000 shares at March 31, 2014 and December 31, 2013; no shares issued and outstanding at March 31, 2014 and December 31, 2013 Preferred Stock, Value, Issued Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, Authorized shares Preferred Stock, Shares Authorized Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Principal amount of debt issued Proceeds from Issuance of Debt Proceeds from Issuance or Sale of Equity Net proceeds after deducting commissions and other transactions costs Net proceeds after deducting offering expenses payable Proceeds from term loans Proceeds from Issuance of Secured Debt Maturities of marketable securities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from issuance of common stock, net of transaction costs, and exercise of common stock options Proceeds from Issuance of Common Stock Proceeds resulting from exercise of stock options Proceeds from Stock Options Exercised Estimated useful lives Property, Plant and Equipment, Useful Life Property and equipment, gross Property, Plant and Equipment, Gross Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Property, Plant and Equipment, Net Property and equipment, net Property and equipment, net Property and Equipment Schedule of property and equipment Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Axis] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] Property and Equipment Property, Plant and Equipment [Line Items] Quarterly Financial Data (unaudited) Quarterly Financial Information [Text Block] Quarterly Financial Data (unaudited) Range [Axis] Range [Domain] Related Party Transactions Related Party Transactions Disclosure [Text Block] Related Party Transactions Related Party Transaction [Line Items] Related Party [Axis] Consulting fees paid Related Party Transaction, Expenses from Transactions with Related Party Related Party [Domain] Related Party Transactions Payment of term loans Repayments of Secured Debt Payment of capital lease obligations Repayment of remaining principal outstanding under existing equipment leases Repayments of Long-term Capital Lease Obligations Counterparty Name [Domain] Research and development Research and Development Expense [Member] Research and Development Costs Research and Development Expense, Policy [Policy Text Block] Research and development credits Research Tax Credit Carryforward [Member] Research and development Research and Development Expense (Excluding Acquired in Process Cost) Unvested restricted common stock Restricted stock awards Restricted stock Restricted Stock [Member] Cash and Cash Equivalents [Domain] Accumulated deficit Retained Earnings [Member] Accumulated deficit Accumulated deficit Retained Earnings (Accumulated Deficit) Grant revenue Revenue from Grants Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Collaboration Revenue Revenues [Abstract] Exercisable at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Expected life in years Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Expiration period Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Exercisable at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Outstanding at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Revenues: Revenue, Net [Abstract] Schedule of unrecognized stock-based compensation expense Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block] Summary of the outstanding securities not included in the computation of diluted net loss per common share as their inclusion would be anti-dilutive Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Investments [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Summary of stock option activity Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of weighted average assumptions used to estimate fair value of each employee stock option award Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of future principal payments under the GECC and Oxford Term Loans Schedule of Maturities of Long-term Debt [Table Text Block] Schedule of differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Summary of unvested restricted share activity Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Schedule of quarterly results of operations Schedule of Quarterly Financial Information [Table Text Block] Cash, Cash Equivalents and Marketable Securities Schedule of Investments [Line Items] Summary of cash, cash equivalents and available-for-sale marketable securities Cash, Cash Equivalents and Investments [Table Text Block] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Related Party Transactions, by Related Party [Table] Property, Plant and Equipment [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Term loans, net of current portion Long term obligation Secured Long-term Debt, Noncurrent Current portion of term loans Less current portion Secured Debt, Current Total principal payments Present value of minimum payments Principal balance Secured Debt Segment Reporting Segment Reporting, Policy [Policy Text Block] Weighted average grant date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted 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Number of Shares Outstanding, Basic and Diluted Weighted average selling price (in dollars per share) Weighted Average Selling Price Per Share Represents the weighted average selling price of a single share of a number of saleable stocks of a company.