Accrued Clinical Trials Current Clinical trial costs Represents the carrying value as of the balance sheet date of obligations incurred through that date and payable for clinical trials. It is used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, if longer). Accrued Service Provider Obligations Current Service provider obligations Represents the carrying value as of the balance sheet date of liabilities incurred through that date and payable for service provider obligations. It is used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, if longer). Represents the carrying value as of the balance sheet date of obligations incurred through that date and payable for sponsored research agreements. It is used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, if longer). Accrued Sponsored Research Agreements Current Costs for sponsored research and license agreements Amortization Related to Share Based Matching Contributions The amount of noncash employee related expense charged against earnings during the reporting period for the vested portion of employer matching contributions in common stock under a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Amortization related to 401(k) contributions Angiochem Inc [Member] Angiochem Represents information pertaining to the Angiochem, Inc. April 2013 Restructuring Plan [Member] April 2013 Restructuring Represents information pertaining to the April 2013 restructuring plan. Noncash or Part Noncash Agreement to Divest of Human Embryonic Stem Cell Assets and Autologous Cellular Immunotherapy Program [Member] Represents the asset contribution agreement among Entity, BioTime and Asterias in which the Entity would divest interest in human embryonic stem cell assets and autologous cellular immunotherapy program in exchange for stock and royalties. Contribution Agreement Asterias [Member] Represents Asterias Biotherapeutics, Inc., majority owned by BioTime following the completion of the Asset Contribution Agreement. Asterias Asterias contributions Available For Sale Securities Continuous Unrealized Loss Position Aggregate Loss Total - Gross Unrealized Losses Amount of gross unrealized loss on securities classified as available-for-sale securities that have been in a loss position as of the reporting date. Less Than 12 Months - Gross Unrealized Losses Amount of gross unrealized loss on securities classified as available-for-sale securities that have been in a loss position for less than twelve months as of the reporting date. Available For Sale Securities Continuous Unrealized Loss Position Less than Twelve Months Aggregate Losses Amendment Description Represents the original maturity period of securities, which are categorized neither as held-to-maturity nor trading. Available For Sale Securities, Original Maturity Period Original maturity period of marketable securities Amendment Flag Bio Time Contribution of Equity and Other Consideration to Asterias in Exchange for Shares and Warrants [Member] BioTime contribution of common stock, warrants, minority stakes in two subsidiaries, and rights to human embryonic stem cell lines to Asterias in exchange for common stock and warrants issued by Asterias. Also included is BioTime forgiveness of a previous loan to Asterias. Asset contribution agreement BioTime Contributions BioTime [Member] BioTime Represents BioTime, Inc., the parent company of Asterias following the completion of the Asset Contribution Agreement. Represents information pertaining to the California Institute for Regenerative Medicine. California Institute for Regenerative Medicine [Member] CIRM Cash and Cash Equivalents Unrealized Losses Gross Unrealized Losses Represents the gross unrealized losses for cash and cash equivalents. Certificates of Deposit for Credit Card Purchases [Member] Certificate of deposit for credit card purchases Represents the details pertaining to certificate of deposit for credit card purchases. Certificate of deposit for unused equipment line of credit Represents the details pertaining to certificate of deposit for unused equipment line of credit. Certificates of Deposit for Unused Equipment Line of Credit [Member] LICENSE AGREEMENTS Represents the number of days used to calculate the volume weighted average closing price of common stock immediately preceding the issuance date used to determine number of shares to be issued under collaborative arrangement. Collaborative Arrangements Days used to Calculate Weighted Average Closing Price Prior to Issuance Date used to Determine Number of Shares to be Issued Number of days to be considered for closing price of common stock Common Stock Aggregate Offering Price Aggregate offering price of common stock Represents the aggregate offering price for which the entity may elect to issue and sell shares of its common stock under the sales agreement. Concentration Risk Customer Material [Policy Text Block] Concentrations of Customers and Suppliers Description of risks that arise due to the volume of business transacted with particular customers and the entity's reliance on a particular material used in its operations and the availability of that material. The description would generally be expected to be adequate to inform financial statement users as to the general nature of the risk. Represents the number of BioTime subsidiaries in which minority stakes were included as part of the consideration given by BioTime for the acquisition. Consideration Given Number of Subsidiaries Minority Stakes Number of subsidiaries for which minority interests were contributed Consultants and Vendors Represents information pertaining to consultants and vendors. Consultants and Vendors [Member] Consultants Represents information pertaining to consultants. Consultants [Member] Debt Instrument Payment Interest Repayment towards accrued interest Represents the portion of the full loan repayment applied to accrued interest. December 2012 Restructuring Plan [Member] December 2012 Restructuring Represents information pertaining to the December 2012 restructuring plan. Deferred Tax Assets Capitalized License Fees License fees Amount before allocation of valuation allowances of deferred tax asset attributable to the treatment of license fee payments in connection with in-licensed technology. Current Fiscal Year End Date Award Type [Axis] Deferred Tax Assets Capitalized Research and Development Capitalized research and development Amount before allocation of valuation allowances of deferred tax asset attributable to the treatment of research and development costs. Deferred Taxes Valuation Allowance Stock Option Deduction The amount of the valuation allowance recorded for the tax benefit that will be credited to shareholders' equity if the tax benefit subsequently becomes realizable. Examples include 1) adjustments of the opening balance of retained earnings for certain changes in accounting principle or a correction of an error; 2) gains and losses included in comprehensive income but excluded from net income; 3) expenditures that are deductible for income tax purposes that are reported as a reduction of shareholders' equity; 4) expenses for employee stock options recognized differently for financial reporting purposes and income tax purposes; 5) dividends paid on unallocated shares held by an ESOP that are charged to retained earnings and 6) deductible temporary differences that existed at the date of a quasi reorganization. Valuation allowance for deferred tax assets related to benefits of stock option deductions Defined Contribution Plan Accelerated Vesting Amount in Unvested Prior Employer Matches for Employees Affected by Restructuring Operating expenses as a result of accelerated vesting of unvested prior employer matches for employees affected by recent restructurings Represents the accelerated vesting amount in unvested prior employer matches for employees affected by restructuring under the defined contribution plan. Represents the period of service of an employee must complete to be fully vested in an employer matching contribution. Defined Contribution Plan Service Period of Employees to be Fully Vested in Employer Matching Contribution Service period of employees Unvested amount under the defined-contribution savings plan to be amortized Represents the unvested amount of employer matching contributions to be amortized under the defined-contribution savings plan as the corresponding years of service are completed by the employees. Defined Contribution Plan Unvested Employer Matching Contributions Amount to be Amortized Period of vesting of matching contributions Represents the period over which matching contributions invested in common stock will vest ratably for each year of service completed by the employee. Defined Contribution Plan Vesting Period of Matching Contributions Represents information pertaining to the 2006 Directors Plan. Directors Plan 2006 [Member] 2006 Directors Plan Directors Stock Option Plan 1996 [Member] 1996 Directors Plan Represents information pertaining to the 1996 Directors' Stock Option Plan. Document and Entity Information Represents the details pertaining to termination of employees and other benefits associated with exit from or disposal of business activities or restructurings pursuant to a plan. Employee Severance and Other Benefits [Member] Employee Severance And Other Benefits 2002 Plan Represents information pertaining to the 2002 Equity Incentive Plan. Equity Incentive Plan 2002 [Member] Document Period End Date Maximum proportionate share of contingent commercial milestone payments Represents the maximum proportionate share of contingent commercial milestone payments exchanged against sale or disposal of equity investment. Equity Method Investment Maximum Proportionate Share of Contingent Commercial Milestone Payments Equity Method Investment Percentage Sale Proceeds Receivable Percentage of potential proceeds receivable Represents the percentage of potential proceeds receivable by the entity upon the sale of a non-marketable equity investment. First Director Option [Member] First Director Option Represents information pertaining to the stock options to be granted by the entity to a person who first becomes a non-employee director. G E Healthcare U K Limited [Member] GE Healthcare UK Limited Represents information pertaining to the GE Healthcare UK Limited. Geron 401K Plan [Member] Geron 401K Plan Represents information pertaining to the Geron 401K Plan. Gross Unrealized Gains Available For Sale Securities Gross Unrealized Gains Amount of gross unrealized gains from available-for-sale securities as of the reporting date. Gross Unrealized Losses Available For Sale Securities Gross Unrealized Losses Amount of gross unrealized losses from available-for-sale securities as of the reporting date. Represents the charge against earnings resulting from the write-down of assets. Impairment of Assets [Member] Asset Write Downs Incentive Award Plan 2011 [Member] 2011 Plan Represents information pertaining to the 2011 Incentive Award Plan. Entity [Domain] Interest and other receivables The increase (decrease) during the reporting period in the amount due from borrowers for interest payments and in other amounts due to the reporting entity, which are not otherwise defined in the taxonomy. Increase (Decrease) in Accrued Interest Receivable Net and Other Receivables Incremental Acquired in Process Research and Development Expense Acquired in-process research and development expense Represents incremental amount of acquired in-process research and development expense recognized for the excess of the fair market value of common stock issued resulting from the difference between the five-day volume weighted average closing price and the closing price on the date of issuance. Share Based Compensation Arrangement by Share Based Payment Award Options Outstanding, Number Subject to Repurchase Number of shares outstanding subject to repurchase The number of shares outstanding that were subject to repurchase. Arrangements and Non-arrangement Transactions [Domain] Licenses and Royalty Revenue Revenue earned during the period relating to consideration received from another party for the right to use, but not own, certain of the entity's intangible assets. Licensing arrangements include, but are not limited to, rights to use a patent, copyright, technology, manufacturing process, software or trademark. Licensing fees are generally, but not always, fixed as to amount and not dependent upon the revenue generated by the licensing party. An entity may receive licensing fees for licenses that also generate royalty payments to the entity. Royalty revenue is derived from a percentage or stated amount of sales proceeds or revenue generated by the third party using the entity's property. Examples of property from which royalties may be derived include patents and oil and mineral rights. License fees and royalties Line of Credit Facility Description [Text Block] EQUIPMENT LINE The entire disclosure for line of credit facility. Loans Receivable Debt Forgiveness Amount of debt forgiven Represents the principal amount of debt forgiven by BioTime for Asterias. Loss Contingency Maximum Number of Months of Current Base Salary to be Paid under Severance Plan Maximum number of months of an employee's then current base salary to be paid as severance under severance plan. Period of base salary to be considered for severance payments Minimum number of months of an employee's then current base salary to be paid as severance under severance plan. Loss Contingency Minimum Number of Months of Current Base Salary to be Paid under Severance Plan Period of base salary to be considered for severance payments Loss Contingency Triggering Event Employee Termination without Cause Following Change of Control Period Period within which employee is terminated by entity without cause following a change of control Represents the number of months following a change in control when an employee is terminated without cause to be classified as a triggering event for severance payments. Loss Contingency Triggering Event Period Following Change of Control During which No Comparable Employment is Offered by Entity Represents the period following change of control within which an employee is not offered comparable employment (new or continuing) by the entity or its successor or acquired and to be considered as triggering event for severance payments. Period within which no comparable employment is offered by the entity following a change of control Loss Contingency Triggering Event Period Following Change of Control within which Employee Resigns Due to Material Change in Terms of Employment Period within which employee resigns following a change of control due to material change in terms of employment Represents the period within which employee resigns following a change of control due to material change in terms of employment and to be considered as triggering event for severance payments. Market-based restricted stock awards Represents the details pertaining to market-based restricted stock awards. Market Based Restricted Stock [Member] Maximum Commission Rate Represents the percentage of maximum commission rate, based on gross proceeds of sale price per share of common stock sold through MLV & Co. under the sales agreement. Maximum commission rate (as a percent) Non Employee Options [Member] Non-employee options Represents the stock options issued to non-employee. November 2011 Restructuring Plan [Member] November 2011 Restructuring Represents information pertaining to the November 2011 restructuring plan. Number of Customers Number of customers Represents the number of customers that accounted for the majority of the entity's revenues during the period. Represents the number of financial institutions with which cash, restricted cash, cash equivalents and marketable securities placed. Number of Financial Institutions with which Cash, Cash Equivalents and Marketable Securities are Placed Number of financial institutions with which cash, restricted cash, cash equivalents and marketable securities are placed Number of Rulings for which Entity Substituted as Party in Appeal Number of rulings in favor of ViaCyte, Inc. for which the entity was substituted as a party in an appeal Represents the number of rulings in favor of ViaCyte, Inc. for which Asterias was substituted for Geron as a party in an appeal. PSAs Represents the performance-based restricted stock awards, which are awarded by the entity to its employees as a form of incentive compensation. Performance Based Restricted Stock Awards [Member] Performance Based Restricted Stock [Member] Performance-based restricted stock awards Represents the details pertaining to performance-based restricted stock awards. Reclassification of deposits to other current assets Represents the amount of deposits that are expected to be returned within one year and are therefore reclassified to other current assets. Reclassification of Deposits to Other Current Assets Research and Development Asset Acquired Other than Through Business Combination Written Off Non Cash The noncash amount of the write-off for research and development assets that were acquired in a transaction other than a business combination. Issuance of common stock in connection with acquired in-process research technology The amount of upfront payments for research and development assets that were acquired in a transaction other than a business combination. Research and Development Asset Acquired Other than through Business Combination Written Off Upfront Payment Paid upfront payment in cash Represents the number of eliminated positions that are continuing to provide services through various dates in the specified period. Restructuring and Related Cost Number of Eliminated Positions Continuing to Provide Services Through Various Dates in Specified Period Number of employees who continued to provide services Represents the amount of cash expected to be paid in a future period to settle projected restructuring charges to be incurred pursuant to a duly authorized plan. Expected cash payments Restructuring Charges Expected to be Settled with Cash Schedule of Common Stock Reserved for Future Issuance [Table Text Block] Schedule of common stock reserved for future issuance Tabular disclosure of common stock reserved for future issuance, which may include but is not limited to outstanding options and outstanding warrants. Schedule of Derivatives Valuation Assumptions [Table Text Block] Schedule of assumptions used to estimate the fair value of derivatives Tabular disclosure of the assumptions used in the fair value measurement of derivative instruments. Service Based Restricted Stock [Member] Service-based restricted stock awards Represents the details pertaining to service-based restricted stock awards. Share Based Compensation Arrangement by Share Based Payment Award Cliff Period for Vesting of Specific Portion of Options Vesting period for specific portion of options Represents the cliff period that must elapse before vesting of any options. Share Based Compensation Arrangement by Share Based Payment Award Duration of New Offering Period Duration of the new offering period Represents the duration of new offering period in a case where the fair market value of common stock on the purchase date is less than the fair market value at the beginning of the offering period. Duration of the purchase period Represents the duration of the purchase period under the employee stock purchase plan. Share Based Compensation Arrangement by Share Based Payment Award Duration of Purchase Period Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Weighted Average Grant Date Fair Value [Abstract] Weighted Average Grant Date Fair Value Per Share Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Other Disclosures [Abstract] Other disclosures Share Based Compensation Arrangement by Share Based Payment Award Maximum Duration of Offering Period Maximum duration of offering period Represents the maximum duration of the offering period under the employee stock purchase plan. Represents the number of offering periods in which an employee can participate at a time in the purchase plan. Share Based Compensation Arrangement by Share Based Payment Award Maximum Number of Offering Periods in which Employee may Participate at One Time Number of offering periods in which an employee can participate at a time Represents the maximum percentage of annual salary that an employee can choose to have withheld to purchase common stock under the purchase plan. Share Based Compensation Arrangement by Share Based Payment Award Maximum Percentage of Annual Salary that Can be Withheld Maximum percentage of annual salary that can be withheld Minimum exercise price as a percentage of fair market value for employees having more than 10 % outstanding common stock Represents the minimum exercise price as a percentage of fair market value for employees having more than 10 % outstanding common stock. Share Based Compensation Arrangement by Share Based Payment Award Minimum Exercise Price of Options Granted to Employees with Ownership of More than 10 Percentage of Common Stock Represents the minimum percentage of ownership required for granting of options at a price not less than 110 percent of the fair market value of common stock. Share Based Compensation Arrangement by Share Based Payment Award Minimum Percentage of Ownership Required for Granting Options at Minimum 110 Percent of Fair Market Value Minimum percentage of ownership required for granting options at least 110% of fair market value of common stock Represents the number of consecutive purchase periods in an offering period in the purchase plan. Share Based Compensation Arrangement by Share Based Payment Award Number of Consecutive Purchase Periods in each Offering Period Number of consecutive purchase periods in an offering period Share Based Compensation Arrangement by Share Based Payment Award Options Intrinsic Value [Abstract] Aggregate Intrinsic Value Loss on sale of marketable securities Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Options to be granted to purchase shares (in shares) Represents the number of options to be granted to purchase shares in each year during the optionee's service on the Board of Directors. Share Based Compensation Arrangement by Share Based Payment Award Options to be Granted to Purchase Shares Share Based Compensation Arrangement by Share Based Payment Award Options to be Granted to Purchase Shares upon Appointment Options to be granted to purchase shares upon appointment (in shares) Represents the number of options to be granted to purchase shares upon appointment to Board of Directors. Weighted Average Remaining Contractual Life (In years) Share Based Compensation Arrangement by Share Based Payment Award Options Weighted Average Remaining Contractual Life [Abstract] Share Based Compensation Arrangement by Share Based Payment Award Other than Options Weighted Average Remaining Contractual Term [Abstract] Weighted Average Remaining Contractual Term (In years) Entity Well-known Seasoned Issuer Share Based Compensation Arrangement by Share Based Payment Award Period for which Shares must be Held after Purchase before Shares may be Traded Period for which shares must be held after purchase under the Purchase Plan before being eligible to be traded Represents the holding period from the date of purchase under the Purchase Plan before shares may be traded. Entity Voluntary Filers Share Based Compensation Arrangement by Share Based Payment Award Shares Available for Grant [Roll Forward] Shares Available For Grant Entity Current Reporting Status Types of vesting schedules (in count) Represents the types of vesting schedules. Share Based Compensation Arrangement by Share Based Payment Award Types of Vesting Schedules Entity Filer Category Share Based Compensation by Share Based Payment Award Options Maximum Expiration Term for Options Granted to Optionees with Ownership of More than 10 Percentage of Common Stock Maximum expiration term of options granted to employees having more than 10 % outstanding common stock Represents the maximum expiration term of options granted to employees having more than 10 % outstanding common stock. Entity Public Float Share Based Goods and Nonemployee Services Capitalized Cost The total remaining amount of capitalized costs resulting from the transaction in which equity securities were issued to pay for goods or nonemployee services. Prepaid asset relating to operating expense Entity Registrant Name Represents the amount of reclassifications from liabilities to stockholders' equity on exercise of equity based awards issued to pay for goods or nonemployee services. Share Based Goods and Nonemployee Services Transaction Reclassifications from Liabilities to Stockholders Equity Amount of reclassifications from current liabilities to stockholders' equity Entity Central Index Key Stock Issued During Period Value Purchase of Research and Development Assets Value of shares of stock issued during the period as part of a transaction to acquire research and development assets that do not qualify as a business combination. Issuance of common stock for acquired in-process research and development Issuance of common stock for acquired in-process research technology Stock Options Granted upon First Appointment to Board of Directors [Member] First Option Represents information pertaining to the stock options granted upon first appointment to the Board of Directors. Subsequent Director Option [Member] Subsequent Director Option Represents information pertaining to the stock options to be granted by the entity subsequent to the grant upon first appointment to the Board of Directors. TA Sciences Represents information pertaining to Telomerase Activation Sciences, Inc. Telomerase Activation Sciences Inc [Member] Entity Common Stock, Shares Outstanding Term of Warrants Issued by Legal Entity Represents the term of the warrants issued by the legal entity. Term of warrants issued Trans Ova Represents the percentage of potential proceeds receivable by the entity upon the sale of a non-marketable equity investment. Trans Ova Genetics L C [Member] Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, shown as a percentage. Vesting Rights Percentage Percentage of option vesting Represents the details pertaining to ViaGen, Inc., an equity method investee of the entity. Via Gen Inc [Member] ViaGen Represents information pertaining to the warrants issued in April 2005. Warrants Issued in April 2005 [Member] Warrants issued in April 2005 Represents information pertaining to the warrants issued in August 2011. Warrants Issued in August 2011 [Member] Warrants issued in August 2011 Warrants issued in November 2011 Represents information pertaining to the warrants issued in November 2011. Warrants Issued in November 2011 [Member] Warrants Issued in September 2009 [Member] Warrants issued in September 2009 Represents information pertaining to the warrants issued in September 2009. Percentage of investee's stock owned immediately after all stock transactions. Percentage ownership in Asterias Investee Cumulative Percentage Ownership after All Transactions Number of Products Available for Sale Number of therapeutic products available for sale Represents the number of therapeutic products available for commercial sale by the company. Agreements [Axis] Information by type of agreements. Agreements [Domain] This element represents the agreement with parties. Represents the market issuance sales agreement with MLV & Co. At The Market Issuance Sales Agreement [Member] Sales Agreement The number of options granted with an exercise price below or greater than fair market value of the company's common stock on the date of grant. Share Based Compensation Arrangement by Share Based Payment Award Number of Options Granted with Exercise Price Below or Greater than Fair Value at Date of Grant Number of options granted with exercise price other than fair market value of Company's common stock Nonmonetary Transactions [Policy Text Block] Nonmonetary Transactions Disclosure of accounting policy for nonmonetary transactions. Represents the amount of carrying value of stem cell assets as of the balance sheet date. Carrying Value of Stem Cell Assets Carrying value of stem cell assets $1.10 - $1.50 Represents the exercise price range from 1.10 dollars to 1.50 dollars per share. Exercise Price Range from Dollars 1.10 to 1.50 [Member] Document Fiscal Year Focus Exercise Price Range from Dollars 1.51 to 1.70 [Member] $1.51 - $1.70 Represents the exercise price range from 1.51 dollars to 1.70 dollars per share. Document Fiscal Period Focus Exercise Price Range from Dollars 1.71 to 6.39 [Member] $1.71 - $6.39 Represents the exercise price range from 1.71 dollars to 6.39 dollars per share. Exercise Price Range from Dollars 6.40 to 9.32 [Member] $6.40 - $9.32 Represents the exercise price range from 6.40 dollars to 9.32 dollars per share. $1.10 - $9.32 Represents the exercise price range from 1.10 dollars to 9.32 dollars per share. Exercise Price Range from Dollars 1.10 to 9.32 [Member] Lock up Period Following Public Offering Lock-up period Represents the duration of the lock-up period following the underwritten public offering. Gain (Loss) on Assets Surrendered Gain or loss recognized on assets surrendered Represents the amount of gain (loss) recognized on assets surrendered. Liability Relating to Contractual Obligation to Distribute Common Stock Liability relating to contractual obligation to distribute common stock Represents the amount of liability related to contractual obligation to distribute Asterias Series A common stock received in stem cell divestiture. Stock-based compensation related to issuance of common stock and options in exchange for services Stock and Options Issued during Period, Value Issued for Services Value of stock and options issued in lieu of cash for services contributed to the entity. Value includes, but is not limited to, services contributed by vendors and founders. Value of stock related to restricted stock awards forfeited during the period, net of issuances of common stock under equity plans. Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock Stock Issued during Period, Value Restricted Stock Award Forfeitures Net of Issuances of Common Stock Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock (in shares) Stock Issued during Period Shares Restricted Stock Award Forfeitures Net of Issuances of Common Stock Number of shares of stock related to restricted stock awards forfeited during the period, net of issuances of common stock under equity plans. One Time Termination Benefits and Facility Related Charges [Member] A lump sum payment to involuntarily terminated employees and for facility-related charges in conjunction with exit or disposal activities. One-time termination benefits and facility-related charges Carrying value of common stock Common Stock Carrying Value Assigned Represents the carrying value assigned to Asterias Series A common stock received in stem cell divestiture. Legal Entity [Axis] Other Commitments Indemnifications Officers and Directors [Member] Represents the indemnification requirements for officers and directors as described in the Company bylaws and indemnification agreements. Indemnifications to Officers and Directors Document Type Indemnification obligations to officers and directors Other Commitment Indemnification Obligations The amount of indemnification obligations to officers and directors as of the balance sheet date. Sales Agreement [Abstract] Sales Agreement Amount per share assigned to the consideration received for shares issued at a public offering. Public offering price (in dollars per share) Equity Issuance Per Share Amount at Public Offering Number of Shares to be Received Number of shares to be received Represents the number of shares to be received. Number of Shares Held Number of shares held Represents the number of shares held. Corporate Note Securities Due in Less than One Year [Member] Corporate notes (due in less than 1 year) This category includes information about short-term debt securities that are issued by either a domestic or foreign corporate business entity with a date certain promise of repayment and a return to the holder for the time value of money (for example, variable or fixed interest), due in less than one year. Corporate Note Securities Due in One to Two Years [Member] Corporate notes (due in 1 to 2 years) This category includes information about short-term debt securities that are issued by either a domestic or foreign corporate business entity with a date certain promise of repayment and a return to the holder for the time value of money (for example, variable or fixed interest), due in one to two years. Common Stock Distribution Ratio Common stock distribution ratio Represents the distribution ratio for the number of shares of Asterias Series A common stock that shareholders will receive for one share of Geron common stock. Commercial Paper Due in Less than One Year [Member] Commercial paper (due in less than 1 year) Represents information pertaining to unsecured promissory note (generally negotiable) that provides institutions with short-term funds ), due in less than one year. Represents information pertaining to debentures, bonds and other debt securities issued by US government sponsored entities (GSEs), for example, but not limited to, Federal Home Loan Mortgage Corporation (FHLMC or Freddie Mac), Federal National Mortgage Association (FNMA or Fannie Mae), and the Federal Home Loan Bank (FHLB). Excludes debt issued by the Government National Mortgage Association (GNMA or Ginnie Mae), due in one to two years. US Government Sponsored Enterprises Debt Securities Due in One to Two Years [Member] Government-sponsored enterprise securities (due in 1 to 2 years) US Government Sponsored Enterprises Debt Securities Due in Less than One Year [Member] Government-sponsored enterprise securities (due in less than 1 year) Represents information pertaining to debentures, bonds and other debt securities issued by US government sponsored entities (GSEs), for example, but not limited to, Federal Home Loan Mortgage Corporation (FHLMC or Freddie Mac), Federal National Mortgage Association (FNMA or Fannie Mae), and the Federal Home Loan Bank (FHLB). Excludes debt issued by the Government National Mortgage Association (GNMA or Ginnie Mae, due in less than one year. ACCRUED LIABILITIES Accounts Payable and Accrued Liabilities Disclosure [Text Block] Accounts Payable, Current Accounts payable Accounts Receivable [Member] Accounts receivable Accretion (Amortization) of Discounts and Premiums, Investments Accretion and amortization on investments, net Accrued liabilities Accrued Liabilities, Current Accrued liabilities Less accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Unrealized (loss) gain on available-for-sale securities Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Additional Paid in Capital, Common Stock Additional paid-in capital Additional Paid-in Capital [Member] Additional Paid-In Capital Supplemental Investing Activities: Additional Cash Flow Elements, Investing Activities [Abstract] Supplemental Operating Activities: Additional Cash Flow Elements, Operating Activities [Abstract] Debt discount in connection with warrant issuances Adjustments to Additional Paid in Capital, Warrant Issued Stock-based compensation for equity-based awards to employees and directors Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Adjustments to reconcile net loss to net cash used in operating activities: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Stock-based compensation expense included in operating expenses Allocated Share-based Compensation Expense Accretion of discount on long-term debt Amortized debt discount Amortization of Debt Discount (Premium) Potential dilutive securities excluded from diluted loss per share calculation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Assets Assets, Fair Value Disclosure [Abstract] Total assets Assets Current assets: Assets, Current [Abstract] ASSETS Assets [Abstract] Total current assets Assets, Current Total Assets, Fair Value Disclosure Less Than 12 Months - Estimated Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 12 Months or Greater - Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss Net unrealized loss on marketable securities Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes 12 Months or Greater - Estimated Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Estimated Fair Value Available-for-sale Securities Total - Estimated Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Current portion of marketable securities Available-for-sale Securities, Current Amortized Cost Available-for-sale Securities, Amortized Cost Basis Schedule of marketable securities with unrealized losses Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block] Marketable securities with unrealized losses Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] Marketable securities Available-for-sale Securities [Abstract] Noncurrent portion of marketable securities Available-for-sale Securities, Noncurrent Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Counterparty Name [Axis] Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Cash and cash equivalents Cash and cash equivalents at the beginning of the period Cash and cash equivalents at the end of the period Cash and Cash Equivalents, at Carrying Value Estimated Fair Value Cash and Cash Equivalents, Fair Value Disclosure Amortized Cost Cash Equivalents, at Carrying Value Included in cash and cash equivalents Cash and Cash Equivalents [Abstract] CONDENSED STATEMENTS OF CASH FLOWS DATA Cash Flow, Supplemental Disclosures [Text Block] Certificates of deposit Certificates of Deposit [Member] Warrants outstanding (in shares) Number of Shares Class of Warrant or Right, Outstanding Common Stock Class of Stock [Line Items] Class of Warrant or Right [Axis] Class of Warrant or Right [Domain] Exercise price of warrants issued (in dollars per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Exercise Price (in dollars per share) Warrants Class of Warrant or Right [Line Items] Class of Stock [Domain] Class of Warrant or Right [Table] LICENSE AGREEMENTS Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] License agreements Collaborative Arrangement [Member] LICENSE AGREEMENTS Collaborative Arrangement Disclosure [Text Block] Commercial paper (due in less than 1 year) Commercial Paper [Member] Commercial paper COMMITMENTS AND CONTINGENCIES Commitments and contingencies 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 Class A [Member] Series A common stock Common Stock Common stock Common Stock [Member] Common stock Common Stock, Value, Issued Common stock, shares issued Common Stock, Shares, Issued Common stock, shares authorized Common Stock, Shares Authorized Total (in shares) Common Stock, Capital Shares Reserved for Future Issuance Common stock, shares outstanding Balances (in shares) Balances (in shares) Common Stock, Shares, Outstanding Number of shares of entity's common stock outstanding Significant components of deferred tax assets Components of Deferred Tax Assets [Abstract] Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Concentration Risk Type [Domain] Concentration risk Concentration Risk [Line Items] Concentration Risk Benchmark [Domain] Concentration Risk Type [Axis] Concentration Risk [Table] Credit Risk Concentration Risks, Types, No Concentration Percentage [Abstract] Concentration Risk Benchmark [Axis] Concentration risk percentage Concentration Risk, Percentage Principles of Consolidation Consolidation, Policy [Policy Text Block] Revenues from collaborative agreements Contracts Revenue Corporate notes Corporate Note Securities [Member] Corporate notes (due in less than one year) Credit Facility [Axis] Credit Facility [Domain] Translation adjustment Cumulative Translation Adjustment, Net of Tax, Period Increase (Decrease) Customer concentration risk Customer Concentration Risk [Member] Basis of interest rate Debt Instrument, Description of Variable Rate Basis LONG-TERM DEBT Debt Instrument [Line Items] Schedule of Long-term Debt Instruments [Table] Loan disbursed Debt Instrument, Face Amount Fixed interest rate (as a percent) Debt Instrument, Basis Spread on Variable Rate LONG-TERM DEBT Purchased technology Deferred Tax Assets, Goodwill and Intangible Assets Total deferred tax assets Deferred Tax Assets, Gross Other - net Deferred Tax Assets, Other Net deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Research credits Deferred Tax Assets, Tax Credit Carryforwards, Research Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Valuation allowance for deferred tax assets Deferred Tax Assets, Valuation Allowance Matching contribution by employer (as a percent) Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Operating expense recorded for vested portion of employer matching contribution Defined Contribution Plan, Cost Recognized 401(k) Plan Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract] Deposits and other assets Deposits Assets, Noncurrent Depreciation and amortization Depreciation, Nonproduction Depreciation and Amortization Depreciation, Depletion and Amortization [Abstract] Depreciation and Amortization Depreciation, Depletion, and Amortization [Policy Text Block] Derivative liabilities Derivative Financial Instruments, Liabilities [Member] Basic and diluted net loss per share (in dollars per share) Earnings Per Share, Basic and Diluted Net Loss Per Share Earnings Per Share, Policy [Policy Text Block] Net Loss Per Share Earnings Per Share [Abstract] Accrued compensation and benefits Employee-related Liabilities, Current Stock-Based Compensation Stock-Based Compensation Expense Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Stock Options Employee Stock Option [Member] Employee Stock Purchase Plan Purchase Plan Employee Stock [Member] Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options Income tax benefit realized from stock options exercised Compensation cost related to unvested stock awards not yet recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Abstract] Compensation cost not yet recognized, net of estimated forfeitures (in dollars) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Period for recognition of compensation cost on weighted average basis Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Severance Plan Employee Severance [Member] Lab equipment Equipment [Member] EQUITY METHOD INVESTMENT Equity Method Investments and Joint Ventures Disclosure [Text Block] Ownership interest (as a percent) Equity Method Investment, Ownership Percentage Investment, Name [Domain] Equity Component [Domain] EQUITY METHOD INVESTMENT Carrying value of investment in ViaGen at the time of sale to TransOva Equity Method Investment, Amount Sold Total Estimate of Fair Value Measurement [Member] Discontinuation of discovery research and companion diagnostics programs and closure of research laboratory facility Facility Closing [Member] Facility Related Charges Measurement Frequency [Axis] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Hierarchy [Axis] Liability Class [Axis] Recurring basis Fair Value, Measurements, Recurring [Member] Fair Value, Measurement Frequency [Domain] Fair Value by Liability Class [Domain] Fair Value on a Recurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value of derivative liabilities at the beginning of the period Fair value of derivative liabilities at the end of the period Fair value of derivatives Derivatives Fair Value Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value FAIR VALUE MEASUREMENTS Fair Value Hierarchy [Domain] Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Schedule of cash equivalents, restricted cash and marketable securities by security type Fair Value, by Balance Sheet Grouping [Table Text Block] Schedule of rollforward of the balance sheet amounts for financial instruments in Level 3 category Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] Changes in Level 3 Recurring Fair Value Measurements Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Total Unrealized Loss (Gain) Included in Earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Change in Unrealized Loss (Gain) Related to Financial Instruments Held at the end of the period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease) Furniture and computer equipment Furniture and Fixtures [Member] Loss (gain) on retirement/sales of property and equipment, net Gain (Loss) on Disposition of Property Plant Equipment Loss on debt extinguishment Gains (Losses) on Extinguishment of Debt Losses recognized from debt extinguishment General and administrative General and Administrative Expense General and administrative General and Administrative Expense [Member] Loss on write-downs of property and equipment Impairment of Long-Lived Assets Held-for-use Losses recognized under equity method investment Loss on equity method investment Proportionate share of ViaGen operating losses Income (Loss) from Equity Method Investments CONDENSED 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] Cash payments for taxes Income Taxes Paid Income Taxes Income Tax, Policy [Policy Text Block] Deposits and other assets Increase (Decrease) in Deposits Outstanding Accounts payable Increase (Decrease) in Accounts Payable Other current liabilities Increase (Decrease) in Other Current Liabilities Accrued restructuring charges Increase (Decrease) in Restructuring Reserve Deferred revenue Increase (Decrease) in Deferred Revenue Accrued liabilities Increase (Decrease) in Other Accrued Liabilities Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accrued compensation and benefits Increase (Decrease) in Employee Related Liabilities Other current and noncurrent assets Increase (Decrease) in Other Operating Assets Prepaid assets Increase (Decrease) in Prepaid Expense Restricted cash transfer Increase (Decrease) in Restricted Cash Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Accrued interest Interest Payable Interest and other income Interest and Other Income Interest expense Interest Expense, Borrowings Cash paid for interest Interest Paid Domestic federal Federal Internal Revenue Service (IRS) [Member] Investments [Domain] Cash Equivalents and Marketable Securities Investment Holdings [Line Items] Investment Type [Axis] Investment Holdings [Table] Stock-based compensation for services by non-employees Issuance of Stock and Warrants for Services or Claims Leasehold improvements Leasehold Improvements [Member] Total current liabilities Liabilities, Current Total liabilities and stockholders' equity Liabilities and Equity Current liabilities: Liabilities, Current [Abstract] LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Liabilities Liabilities, Fair Value Disclosure [Abstract] License fee revenue Licenses Revenue EQUIPMENT LINE Amounts due for payment under the facility Line of Credit Facility, Amount Outstanding Equipment financing facility Line of Credit [Member] EQUIPMENT LINE Line of Credit Facility [Line Items] Line of Credit Facility [Table] Amount available for borrowing Line of Credit Facility, Remaining Borrowing Capacity LONG-TERM DEBT Long-term Debt [Text Block] Loss Contingency, Nature [Domain] Loss Contingencies [Table] COMMITMENTS AND CONTINGENCIES. Loss Contingencies [Line Items] Loss Contingency Nature [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Maximum Maximum [Member] Minimum Minimum [Member] Money market funds Money Market Funds [Member] 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 decrease in cash and cash equivalents Net Cash Provided by (Used in) Continuing Operations 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 (used in) provided by 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] Net loss Net loss Net Income (Loss) Attributable to Parent Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Noncash or Part Noncash Divestiture, Name [Domain] Unique Name [Axis] Shares issued Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Shares Issued Number of warrants issued Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Warrants Issued DIVESTITURE OF STEM CELL ASSETS Noncash or Part Noncash Divestitures [Line Items] Noncash or Part Noncash Divestitures [Table] DIVESTITURE OF STEM CELL ASSETS DIVESTITURE OF STEM CELL ASSETS Nonmonetary Transactions Disclosure [Text Block] Interest and other receivables Nontrade Receivables, Current Number of operating segments Number of Operating Segments One-time termination benefits One-time Termination Benefits [Member] Operating expenses: Operating Expenses [Abstract] Total operating expenses Operating Expenses Operating expenses Rent expense under operating leases Operating Leases, Rent Expense, Net Loss from operations Operating Income (Loss) Operating Loss Carryforwards [Table] Operating loss carryforwards Operating Loss Carryforwards [Line Items] Future minimum payments under operating lease Aggregate future minimum payments for operating lease obligations under amended agreement Operating Leases, Future Minimum Payments Due Net operating loss carryforwards Operating Loss Carryforwards SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Other Commitments [Axis] Other Commitments [Domain] Other-than-temporary impairment charges recorded for available-for-sale securities Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Reclassification of accumulated foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax Expense for accumulated foreign currency translation adjustments recognized in connection with dissolution of subsidiary Net unrealized gain (loss) on marketable securities Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax Foreign currency translation adjustments Non-refundable upfront payment recognized in other income Other Income Interest and other expense Other Nonoperating Expense Other Significant Noncash Transaction, Name [Domain] Other Other Accrued Liabilities, Current Other Significant Noncash Transaction [Axis] Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Other comprehensive loss Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Other comprehensive income (loss) ACCRUED LIABILITIES Purchases of marketable securities Payments to Acquire Available-for-sale Securities Cash payments Payments for Restructuring Dividends paid to date Payments of Ordinary Dividends, Common Stock Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Plan Name [Domain] Plan Name [Axis] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, $0.001 par value; 3,000,000 shares authorized; no shares issued and outstanding at December 31, 2013 and 2012 Preferred Stock, Value, Issued Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Prepaid assets Prepaid Expense, Current Proceeds from Issuance of Unsecured Debt Proceeds from issuance of long-term debt Proceeds from maturities of marketable securities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from issuance of common stock, net of issuance costs Proceeds from Issuance of Common Stock Cash received from exercise of options (in dollars) Proceeds from Stock Options Exercised Proceeds from sale of investment in licensees Proceeds from Sale of Available-for-sale Securities, Equity Proceeds from sales of marketable securities Proceeds from Sale of Available-for-sale Securities, Debt Proceeds from sales of property and equipment Proceeds from Sale of Property, Plant, and Equipment Proceeds from sales of property and equipment Estimated useful lives of assets Property, Plant and Equipment, Useful Life Property and equipment, gross Property, Plant and Equipment, Gross Property and equipment, net Property, Plant and Equipment, Net Property and equipment, net PROPERTY AND EQUIPMENT Schedule of property and equipment, stated at cost 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] SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) Quarterly Financial Information [Text Block] SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) Range [Axis] Range [Domain] Unrecognized tax benefits Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Related party transactions Related Party Transaction [Line Items] Loan repaid Repayments of Debt Repayment of long-term debt Repayments of Unsecured Debt Geron Reporting Entity [Member] Counterparty Name [Domain] Research and development Research and Development Expense [Member] Research and Development Expenses Research and Development Expense, Policy [Policy Text Block] Research and development Research Tax Credit Carryforward [Member] Organization Research and Development [Abstract] Research and development Research and Development Expense (Excluding Acquired in Process Cost) Acquired in-process research and development Total upfront payment relating to acquired in-process research and development expensed Research and Development Asset Acquired Other than Through Business Combination, Written-off Restricted cash Restricted Cash and Investments [Abstract] Restricted Stock Awards Restricted Stock [Member] Restricted cash Carrying value of restricted cash Amortized Cost Restricted Cash and Cash Equivalents, Current Restricted Cash Restricted Cash and Cash Equivalents Items [Line Items] Restricted Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Estimated Fair Value Restricted Investments, at Fair Value Number of positions eliminated, inception to date Restructuring and Related Cost, Number of Positions Eliminated, Inception to Date Number of positions eliminated (as a percent) Restructuring and Related Cost, Number of Positions Eliminated, Period Percent Restructuring charges Restructuring Charges Accrued restructuring charges Accrual balance at the beginning of the period Accrual balance at the end of the period Restructuring Reserve, Current Restructuring Plan [Domain] Adjustments or non-cash credits Restructuring Reserve, Accrual Adjustment Restructuring Type [Axis] RESTRUCTURING Restructuring Plan [Axis] Outstanding restructuring liability Restructuring Reserve [Roll Forward] RESTRUCTURING Restructuring and Related Activities Disclosure [Text Block] RESTRUCTURING Restructuring Cost and Reserve [Line Items] Restructuring charges Restructuring Charges [Member] Accumulated Deficit Retained Earnings [Member] Accumulated deficit Retained Earnings (Accumulated Deficit) Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Total revenues Revenues Revenues Revenues: Revenues [Abstract] STOCKHOLDERS' EQUITY Shareholders' Equity and Share-based Payments [Text Block] Options exercisable at the end of the period (in dollars) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Expected term Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Weighted Average Exercise Price Per Share (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price Percentage applied to common stock market value in calculating purchase price under purchase plan Exercise price of options as a percentage of fair market value Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent Expiration term of options from date of grant Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Options fully vested and expected to vest at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Options exercisable at the end of the period Balance at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted Average Remaining Contractual Life (In years) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term Schedule of Available-for-sale Securities [Table] Schedule of financial instruments measured at fair value on recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of aggregate restricted stock activity Schedule of Nonvested Share Activity [Table Text Block] Supplemental schedule of non-cash operating and investing activities Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of assumptions used to estimate the fair value of stock options granted Schedule of assumptions used to estimate the fair value of employee stock purchases under the Purchase Plan Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Schedule of non-employee options to purchase common stock considered as derivatives and classified as current liabilities Schedule of Derivative Liabilities at Fair Value [Table Text Block] Schedule of significant components of the entity's deferred tax assets Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of reconciliation of the beginning and ending amounts of unrecognized tax benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Schedule of accrued liabilities Schedule of Accrued Liabilities [Table Text Block] Schedule of aggregate option and award activity Schedule of Share-based Compensation, Activity [Table Text Block] Schedule of selected quarterly financial information (unaudited) Schedule of Quarterly Financial Information [Table Text Block] Marketable securities Schedule of Available-for-sale Securities [Line Items] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Schedule of components of accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Investment, Name [Axis] Schedule of Equity Method Investments [Table] EQUITY METHOD INVESTMENT Schedule of Equity Method Investments [Line Items] Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Restructuring and Related Costs [Table] Property, Plant and Equipment [Table] Schedule of components of restricted cash Schedule of Restricted Cash and Cash Equivalents [Table Text Block] Summary of components of accrued restructuring charges Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Restricted Cash and Cash Equivalents [Table] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Schedule of Stock by Class [Table] Schedule of warrants outstanding to purchase common stock and classified as equity Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block] Schedule of information about stock options outstanding by exercise price range Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Schedule of Share-based Goods and Nonemployee Services Transaction [Table] Carrying values of investments in non-marketable nonpublic companies Securities Owned Not Readily Marketable Non-Marketable Investments in Licensees Securities Owned and Other Investments Not Readily Marketable [Abstract] SEGMENT INFORMATION SEGMENT INFORMATION Segment Reporting Disclosure [Text Block] Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Weighted Average Exercise Price Per Share Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Awards granted (in shares) 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) Weighted average estimated fair value of purchase rights (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 Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Options granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Options canceled/forfeited (in dollars per share) Non-vested restricted stock at the beginning of the period (in shares) Non-vested restricted stock at the end of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Non-vested restricted stock at the end of the period (in shares) Expected volatility range, maximum (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum Expected volatility range, minimum (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Stock-based compensation for employees and directors Share-based Compensation Risk-free interest rate range, maximum (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum Vesting period of awards Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Option vesting period Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Options granted (in shares) Options granted (in shares) Stock-Based Compensation STOCKHOLDERS' EQUITY Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Non-vested restricted stock at the beginning of the period (in dollars per share) Non-vested restricted stock at the end of the period (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 Non-vested restricted stock at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms Canceled/forfeited (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 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Canceled/forfeited (in shares) Awards canceled/forfeited (in shares) Closing stock price (in dollars per share) Share Price Public offering price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum Risk-free interest rate range, minimum (as a percent) Options exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Expected term Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Options exercisable at the end of the period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Dividend yield (as a percent) Total fair value of restricted stock that vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Options canceled/forfeited (in shares) Options canceled/forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Options exercisable at the end of the period (in shares) Shares that were available for issuance Options and awards available for grant (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Balance at the beginning of the period (in shares) Balance at the end of the period (in shares) Total pretax intrinsic value of stock options exercised (in dollars) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Expected volatility (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Shares of common stock reserved for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Assumptions used to estimate fair value of awards Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Weighted average estimated fair value of employee stock options granted (in dollars per share) Exercise Price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Balance at the beginning of the period (in dollars per share) Balance at the end of the period (in dollars per share) Stock-Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Stock-based compensation expense related to extension of the post-termination exercise period Stock-based compensation expense related to extension of the post-termination exercise period Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Incremental Compensation Cost Options Outstanding Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, End of Period [Abstract] Number of Shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Balance at the beginning of the period (in shares) Balance at the end of the period (in shares) Outstanding stock options (in shares) Number of shares outstanding Exercise Price Range Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Options fully vested and expected to vest at the end of the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Balance at the end of the period (in dollars) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Exercise Price Range [Axis] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Equity Award [Domain] Exercise price, low end of range (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit Options fully vested and expected to vest at the end of the period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Options fully vested and expected to vest at the end of the period (in dollars) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Stock-based compensation for services by non-employees Share-based Goods and Nonemployee Services Transaction, Expense (Deprecated 2013-01-31) Share-based Goods and Nonemployee Services Transaction, Supplier [Domain] Number of Shares Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options Expected volatility (as a percent) Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Volatility Rate Risk-free interest rate (as a percent) Share-based Goods and Nonemployee Services Transaction, Valuation Method, Risk Free Interest Rate Dividend yield (as a percent) Share-based Goods and Nonemployee Services Transaction, Valuation Method, Expected Dividend Rate Options granted (in shares) Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued Stock-Based Compensation to Service Providers Share-based Goods and Nonemployee Services Transaction [Line Items] Derivatives Exercise price, high end of range (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit Supplier [Axis] Shares issued under plan Shares, Issued State State and Local Jurisdiction [Member] Statement [Table] Statement Statement [Line Items] CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY CONDENSED STATEMENTS OF CASH FLOWS CHANGE IN CASH AND CASH EQUIVALENTS Equity Components [Axis] CONDENSED STATEMENTS OF COMPREHENSIVE LOSS CONDENSED BALANCE SHEETS Class of Stock [Axis] Stock-based compensation related to issuance of common stock and options in exchange for services (in shares) Stock Issued During Period, Shares, Issued for Services 401(k) contribution (in shares) Stock Issued During Period, Shares, Employee Benefit Plan Issuance of common stock for services rendered to date or to be received in future periods Stock Issued During Period, Value, Issued for Services Issuance of common stock for 401(k) matching contributions Stock Issued During Period, Value, Employee Benefit Plan Issuance of common stock under equity plans, net of cancellations of non-vested restricted stock (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Stock Issued During Period, Shares, New Issues Underwritten public offering (in shares) Issuance of common stock in connection with acquired in-process research technology (in shares) Shares of common stock issued against acquired in-process research and development Stock Issued During Period, Shares, Purchase of Assets Issuance of common stock under equity plans, net of cancellations of non-vested restricted stock Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance of common stock for acquired in-process research and development Issuance of common stock in connection with acquired in-process research technology Stock Issued During Period, Value, Purchase of Assets Net cash proceeds from public offering after deducting the underwriting discount and offering expenses Issuance of common stock in connection with public offering, net of issuance costs of $6,300 Stock Issued During Period, Value, New Issues Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Total stockholders' equity Stockholders' Equity Attributable to Parent Balances Balances Accumulated Other Comprehensive Income (Loss) Stockholders' Equity, Policy [Policy Text Block] STOCKHOLDERS' EQUITY SUBSEQUENT EVENTS Subsequent Events [Text Block] SUBSEQUENT EVENTS Subsequent Event [Table] Subsequent event Subsequent Event [Line Items] Subsequent event Subsequent Event [Member] Subsequent events Subsequent Event Type [Domain] Subsequent Event Type [Axis] Percentage ownership in Asterias Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions CONDENSED STATEMENTS OF CASH FLOWS DATA Supplemental disclosure of cash flow information: Supplemental cash flow information Supplemental Cash Flow Information [Abstract] Tax credit carryforwards Tax Credit Carryforward, Amount Tax Credit Carryforward, Name [Domain] Tax credit carryforwards Tax Credit Carryforward [Line Items] Tax Credit Carryforward [Table] Tax Credit Carryforward [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] Type of Restructuring [Domain] Unrealized (loss) gain on derivatives Unrealized gain on derivatives Unrealized Gain (Loss) on Derivatives Interest and penalties charged Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Interest and penalties expense related to unrecognized tax benefits Increase related to current year tax positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Unrecognized Tax Benefits that Would Impact Effective Tax Rate Unrecognized tax benefits, if recognized would impact effective tax rate Balance at the beginning of the period Balance at the end of the period Unrecognized Tax Benefits Increase related to prior year tax positions Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Use of Estimates Use of Estimates, Policy [Policy Text Block] Government-sponsored enterprise securities (due in less than 1 year) US Government-sponsored Enterprises Debt Securities [Member] Government-sponsored enterprise securities Valuation allowance Valuation Allowance [Abstract] Increase (decrease) in valuation allowance Valuation Allowance, Deferred Tax Asset, Change in Amount Outstanding loan Variable Interest Entity, Financial or Other Support, Amount Shares used in computing basic and diluted net loss per share (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted