Geron (GERN) 10-Q 5 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 31, 2014
Document and Entity Information	'	'
Entity Registrant Name	'GERON CORP	'
Entity Central Index Key	'0000886744	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-14	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	157,211,487
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'

CONDENSED_BALANCE_SHEETS

CONDENSED BALANCE SHEETS (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$7,600	$12,990
Restricted cash	265	795
Current portion of marketable securities	118,801	52,234
Interest and other receivables	787	564
Prepaid assets	739	474
Total current assets	128,192	67,057
Noncurrent portion of marketable securities	15,801	'
Property and equipment, net	63	92
Deposits and other assets	191	195
Total assets	144,247	67,344
Current liabilities:	'	'
Accounts payable	2,365	1,397
Accrued compensation and benefits	2,685	3,946
Accrued restructuring charges	'	94
Accrued liabilities	2,018	1,783
Fair value of derivatives	1	367
Total current liabilities	7,069	7,587
Commitments and contingencies	'	'
Stockholders' equity:	'	'
Common stock	157	131
Additional paid-in capital	1,056,543	952,403
Accumulated deficit	-919,486	-892,763
Accumulated other comprehensive loss	-36	-14
Total stockholders' equity	137,178	59,757
Total liabilities and stockholders' equity	$144,247	$67,344

CONDENSED_STATEMENTS_OF_OPERAT

CONDENSED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:	'	'	'	'
License fees and royalties	$160	$181	$975	$1,058
Operating expenses:	'	'	'	'
Research and development	5,994	5,338	16,356	18,066
Restructuring charges	'	116	'	1,032
General and administrative	4,073	3,460	11,920	11,643
Total operating expenses	10,067	8,914	28,276	30,741
Loss from operations	-9,907	-8,733	-27,301	-29,683
Unrealized gain (loss) on derivatives	289	-208	366	-207
Interest and other income	91	699	273	836
Interest and other expense	-22	-12	-61	-44
Net loss	($9,549)	($8,254)	($26,723)	($29,098)
Basic and diluted net loss per share (in dollars per share)	($0.06)	($0.06)	($0.18)	($0.23)
Shares used in computing basic and diluted net loss per share (in shares)	156,843,989	128,293,074	152,338,668	128,146,333

CONDENSED_STATEMENTS_OF_COMPRE

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
CONDENSED STATEMENTS OF COMPREHENSIVE LOSS	'	'	'	'
Net loss	($9,549)	($8,254)	($26,723)	($29,098)
Net unrealized (loss) gain on marketable securities	-16	1	-22	-52
Comprehensive loss	($9,565)	($8,253)	($26,745)	($29,150)

CONDENSED_STATEMENTS_OF_CASH_F

CONDENSED STATEMENTS OF CASH FLOWS CHANGE IN CASH AND CASH EQUIVALENTS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:	'	'
Net loss	($26,723)	($29,098)
Adjustments to reconcile net loss to net cash used in operating activities:	'	'
Depreciation and amortization	38	357
Accretion and amortization on investments, net	2,221	948
Loss (gain) on retirement/sales of property and equipment, net	3	-759
Loss on write-downs of property and equipment	'	200
Stock-based compensation for services by non-employees	172	136
Stock-based compensation for employees and directors	5,752	3,456
Amortization related to 401(k) contributions	99	449
Unrealized (gain) loss on derivatives	-366	207
Changes in assets and liabilities:	'	'
Other current and noncurrent assets	-484	904
Other current liabilities	161	-6,679
Net cash used in operating activities	-19,127	-29,879
Cash flows from investing activities:	'	'
Restricted cash transfer	530	-1
Purchases of property and equipment	-12	-56
Proceeds from sales of property and equipment	'	1,116
Purchases of marketable securities	-159,172	-57,446
Proceeds from sales of marketable securities	4,513	'
Proceeds from maturities of marketable securities	70,048	73,301
Net cash (used in) provided by investing activities	-84,093	16,914
Cash flows from financing activities:	'	'
Proceeds from issuance of common stock, net of issuance costs	97,830	493
Net cash provided by financing activities	97,830	493
Net decrease in cash and cash equivalents	-5,390	-12,472
Cash and cash equivalents at the beginning of period	12,990	22,063
Cash and cash equivalents at the end of the period	$7,600	$9,591

SUMMARY_OF_SIGNIFICANT_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2014
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Basis of Presentation
	The terms “Geron”, the “Company”, “we” and “us” as used in this report refer to Geron Corporation. The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management of Geron, all adjustments (consisting only of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three and nine month periods ending September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014 or any other period. These financial statements and notes should be read in conjunction with the financial statements for each of the three years ended December 31, 2013, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2013 has been derived from audited financial statements at that date.
	Net Loss Per Share
	Basic earnings (loss) per share is calculated based on the weighted average number of shares of common stock outstanding during the period. Diluted earnings (loss) per share is calculated based on the weighted average number of shares of common stock and potential dilutive securities outstanding during the period. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase common stock and are determined using the treasury stock method at an average market price during the period.
	Because we are in a net loss position, diluted loss per share excludes the effects of potential dilutive securities. Had we been in a net income position, diluted earnings per share would have included the shares used in the computation of basic net loss per share as well as an additional 1,926,886 and 138,344 shares for the three months ended September 30, 2014 and 2013, respectively, and 3,205,962 and 7,183 shares for the nine months ended September 30, 2014 and 2013, respectively, related to outstanding stock options, restricted stock awards and warrants (as determined using the treasury stock method at the estimated average market value).
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On a regular basis, management evaluates these estimates and assumptions. Actual results could differ from those estimates.
	Fair Value of Financial Instruments
	Cash Equivalents and Marketable Securities
	We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. We are subject to credit risk related to our cash equivalents and marketable securities. We place our cash and cash equivalents in money market funds and cash operating accounts. Our marketable securities include U.S. government-sponsored enterprise securities, commercial paper and corporate notes with original maturities ranging from five to 19 months.
	We classify our marketable securities as available-for-sale. We record available-for-sale securities at fair value with unrealized gains and losses reported in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included in interest and other income and are derived using the specific identification method for determining the cost of securities sold and have been insignificant to date. Dividend and interest income are recognized when earned and included in interest and other income in our condensed statements of operations. We recognize a charge when the declines in the fair values below the amortized cost basis of our available-for-sale securities are judged to be other-than-temporary. We consider various factors in determining whether to recognize an other-than-temporary charge, including whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. Declines in market value associated with credit losses judged as other-than-temporary result in a charge to interest and other income. Other-than-temporary charges not related to credit losses are included in accumulated other comprehensive income (loss) in stockholders’ equity. We have not recorded any other-than-temporary impairment charges on our available-for-sale securities for the three and nine months ended September 30, 2014 and 2013. See Note 2 on Fair Value Measurements.
	Non-Marketable Equity Investments
	Non-marketable equity investments in companies in which we own less than 20% of the outstanding voting stock and do not otherwise have the ability to exert significant influence over the investees are carried at cost, as adjusted for other-than-temporary impairments. We apply the equity method of accounting for non-marketable equity investments in companies in which we own more than 20% of the outstanding voting stock or otherwise have the ability to exert significant influence over the investees. Under this method, we increase (decrease) the carrying value of our investment by our proportionate share of the investee’s earnings (losses). If losses exceed the carrying value of the investment, losses are then applied against any advances to the investee, including any commitment to provide financial support, until those amounts are reduced to zero. Commitments to provide financial support include formal guarantees, implicit arrangements, reputational expectations, intercompany relationships or a consistent past history of providing financial support. The equity method is then suspended until the investee has earnings. Any proportionate share of investee earnings is first applied to the share of accumulated losses not recognized during the period the equity method was suspended. We recognize previously suspended losses to the extent additional investment is determined to represent the funding of prior losses. See Note 3 on Divestiture of Stem Cell Assets.
	Fair Value of Derivatives
	For non-employee options classified as assets or liabilities, the fair value of these instruments is recorded on the condensed balance sheet at inception and adjusted to fair value at each financial reporting date. The change in fair value of the non-employee options is recorded in the condensed statements of operations as unrealized gain (loss) on derivatives. Fair value of non-employee options is estimated using the Black Scholes option-pricing model. The non-employee options continue to be reported as an asset or liability until such time as the instruments are exercised or expire or are otherwise modified to remove the provisions which require this treatment, at which time these instruments are marked to fair value and reclassified from assets or liabilities to stockholders’ equity. For non-employee options classified as permanent equity, the fair value of the non-employee options is recorded in stockholders’ equity as of their respective vesting dates and no further adjustments are made. See Note 2 on Fair Value Measurements.
	Nonmonetary Transactions
	We account for nonmonetary transactions based on the fair values of the assets (or services) involved. The cost of a nonmonetary asset acquired in exchange for another nonmonetary asset is the fair value of the asset surrendered to obtain it with a gain or loss recognized on the exchange. We use the fair value of the asset received to measure the cost if it is more clearly evident than the fair value of the asset surrendered. If the fair value of neither the assets received nor the assets relinquished is determinable within reasonable limits, we use the recorded amount (or carrying value) of the nonmonetary assets relinquished to account for the exchange. Similarly, we use carrying value for an exchange of controlled assets that do not meet the definition of a business for a non-controlling non-marketable equity interest in a company with no gain or loss recognized on the exchange. See Note 3 on Divestiture of Stem Cell Assets.
	Revenue Recognition
	We have entered into several license agreements with various oncology, diagnostics, research tools and biologics production companies. With certain of these agreements, we receive non-refundable license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, milestone payments, royalties on future sales of products, or any combination of these items. Upfront non-refundable signing, license or non-exclusive option fees are recognized as revenue when rights to use the intellectual property related to the license have been delivered and over the term of the agreement if we have continuing performance obligations. We recognize revenue under collaborative agreements as the related research and development costs for services are rendered. Milestone payments, which are subject to substantive contingencies, are recognized as revenue upon completion of specified milestones, representing the culmination of the earnings process, according to contract terms. Royalties are generally recognized upon receipt of the related royalty payment. Deferred revenue represents the unearned portion of research and license payments received. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash.
	Restricted Cash
	Restricted cash consists of funds maintained in separate certificate of deposit accounts for specified purposes. The components of restricted cash were as follows:
		September 30,			December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases	265			265
		$	265		$	795
	In the third quarter of 2014, we closed the certificate of deposit for our unused equipment line of credit upon maturity and transferred the cash proceeds to our cash operating accounts. This action also canceled the availability of the equipment line of credit.
	Research and Development Expenses
	Research and development expenses consist of expenses incurred in identifying, developing and testing product candidates resulting from our independent efforts as well as efforts associated with collaborations. These expenses include, but are not limited to, acquired in-process research and development deemed to have no alternative future use, payroll and personnel expense, lab supplies, preclinical studies, clinical trials, including support for investigator-sponsored clinical trials, raw materials to manufacture clinical trial drugs, manufacturing costs for research and clinical trial materials, sponsored research at other labs, consulting, costs to maintain technology licenses and research-related overhead. Research and development costs are expensed as incurred, including payments made under our license agreements.
	Clinical Trial Costs
	A significant component of our research and development expenses has historically been clinical trial costs. Substantial portions of our preclinical studies and all of our clinical trials have been performed by third-party contract research organizations, or CROs, and other vendors. We accrue expenses for preclinical studies performed by our vendors based on certain estimates over the term of the service period and adjust our estimates as required. We accrue expenses for clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, the number of active clinical sites and the duration for which the patients have been enrolled in the study. Pass through costs from CROs include, but are not limited to, regulatory expenses, investigator fees, lab fees, travel costs and other miscellaneous costs, including shipping and printing fees. We accrue pass through costs based on estimates of the amount of work completed for the clinical trial. We monitor patient enrollment levels and related activities to the extent possible through internal reviews, review of contractual terms and correspondence with CROs. We base our estimates on the best information available at the time. However, additional information may become available to us which would allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain.
	Depreciation and Amortization
	We record property and equipment at cost and calculate depreciation using the straight-line method over the estimated useful lives of the assets, generally four years. Leasehold improvements are amortized over the shorter of the estimated useful life or remaining term of the lease.
	Stock-Based Compensation
	We recognize stock-based compensation expense on a straight-line basis over the requisite service period, which is generally the vesting period. The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options, restricted stock awards and employee stock purchases for the three and nine months ended September 30, 2014 and 2013 which was allocated as follows:
		Three Months Ended September 30,					Nine Months Ended September 30,
	(In thousands)	2014			2013		2014		2013
	Research and development	$	653		$	483	$	1,932	$	1,394
	Restructuring charges	—			—		—		28
	General and administrative	1,356			739		3,820		2,034
	Stock-based compensation expense included in operating expenses	$	2,009		$	1,222	$	5,752	$	3,456
	Modifications to the post-termination exercise period of outstanding options held by certain members of our executive management team resulted in additional stock-based compensation expense of $205,000 for the three and nine months ended September 30, 2013. In addition, in connection with the April 2013 restructuring, the post-termination exercise period for certain stock options previously granted to terminated employees was extended through the end of December 2013 resulting in the recognition of $28,000 of non-cash stock-based compensation expense for the nine months ended September 30, 2013. Stock-based compensation expense resulting from these modifications has been reflected in the table above. See Note 4 on Restructuring for a further discussion of the April 2013 restructuring.
	As stock-based compensation expense recognized in our condensed statements of operations for the three and nine months ended September 30, 2014 and 2013 is based on awards ultimately expected to vest, it has been reduced for estimated forfeitures, but at a minimum, reflects the grant-date fair value of those awards that actually vested in the period. Forfeitures have been estimated at the time of grant based on historical data and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	Stock Options
	We grant options with service-based vesting under our equity plans to employees, non-employee directors and consultants. The vesting period for employee options is generally four years. The fair value of options granted during the nine months ended September 30, 2014 and 2013 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.898 to 0.922		0.742 to 0.759
	Risk-free interest rate range	1.64% to 1.92%		0.80% to 1.81%
	Expected term	5.5 yrs		6 yrs
	Employee Stock Purchase Plan
	The fair value of employees’ purchase rights during the nine months ended September 30, 2014 and 2013 has been estimated using the Black Scholes option-pricing model with the following assumptions:
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.835 to 1.666		0.506 to 1.391
	Risk-free interest rate range	0.06% to 0.15%		0.09% to 0.21%
	Expected term range	6 – 12 mos		6 – 12 mos
	Dividend yield is based on historical cash dividend payments. The expected volatility is based on historical volatilities of our stock since traded options on Geron stock do not correspond to option terms and the trading volume of options is limited. The risk-free interest rate is based on the U.S. Zero Coupon Treasury Strip Yields for the expected term in effect on the date of grant for an award. The expected term of options is derived from actual historical exercise and post-vesting cancellation data and represents the period of time that options granted are expected to be outstanding. The expected term of employees’ purchase rights is equal to the purchase period.
	Restricted Stock Awards
	We have granted restricted stock awards to employees and non-employee directors with service-based vesting schedules that generally vest annually over four years. The fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. The fair value is amortized as stock-based compensation expense over the requisite service period of the award, which is generally the vesting period, on a straight-line basis and is reduced for estimated forfeitures, as applicable.
Non-Employee Stock-Based Awards
For our non-employee stock-based awards, the measurement date on which the fair value of the stock-based award is calculated is equal to the earlier of (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. We recognize stock-based compensation expense for the fair value of the vested portion of non-employee awards in our condensed statements of operations.
Recent Accounting Pronouncements
In April 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2014-08, Presentation of Financial Statements and Property, Plant, and Equipment: Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 raised the threshold for a disposal of assets to qualify as a discontinued operation and requires new disclosures for both discontinued operations and disposals of individually significant components of a business that do not qualify as discontinued operations. Under the new guidance, only disposals of assets representing a strategic shift in operations that has a major effect on the entity’s operations and financial results should be presented as discontinued operations. If the disposal does qualify as a discontinued operation, the entity will be required to provide expanded disclosures, as well as disclosure of the pretax income attributable to the disposal of a significant part of an entity that does not qualify as a discontinued operation. ASU 2014-08 will be effective for us beginning January 1, 2015 and subsequent interim periods. We do not expect the adoption of ASU 2014-08 to have a material effect on our financial statements.
In May 2014, the FASB issued Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers, or ASU 2014-09. ASU 2014-09 provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 will require an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This update creates a five-step model that requires entities to exercise judgment when considering the terms of the contract(s). The five-step model includes (i) identifying the contract(s) with the customer, (ii) identifying the separate performance obligations in the contract, (iii) determining the transaction price, (iv) allocating the transaction price to the separate performance obligations, and (v) recognizing revenue when each performance obligation is satisfied. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 will be effective for us beginning January 1, 2017 and subsequent interim periods. We have the option to apply the provisions of ASU 2014-09 either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of applying this accounting standard recognized at the date of initial application. Early adoption is not permitted. We are currently evaluating the transition method and the impact that the adoption of ASU 2014-09 will have on our financial statements.
In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, or ASU 2014-15. ASU 2014-15 is intended to define management’s responsibility to evaluate whether there is substantial doubt about an organization’s ability to continue as a going concern and to provide related footnote disclosures. Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 provides guidance to an organization’s management, with principles and definitions that are intended to reduce diversity in the timing and content of disclosures that are commonly provided by organizations in financial statement footnotes. ASU 2014-15 is effective for us beginning December 31, 2016 and subsequent interim periods. Early adoption is permitted. We are currently in the process of evaluating the impact of adoption of ASU 2014-15 on our financial statements and related disclosures.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2014
FAIR VALUE MEASUREMENTS	'
FAIR VALUE MEASUREMENTS	'
	2. FAIR VALUE MEASUREMENTS
	We categorize financial instruments recorded at fair value on our condensed balance sheets based upon the level of judgment associated with inputs used to measure their fair value. The categories are as follows:
	Level 1	—	Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis.
	Level 2	—	Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life.
	Level 3	—	Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.
	A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Below is a description of the valuation methodologies used for financial instruments measured at fair value on our condensed balance sheets, including the category for such financial instruments.
	Cash Equivalents and Marketable Securities
	Certificates of deposit and money market funds are categorized as Level 1 within the fair value hierarchy as their fair values are based on quoted prices available in active markets. U.S. Treasury securities, U.S. government-sponsored enterprise securities, municipal securities, corporate notes and commercial paper are categorized as Level 2 within the fair value hierarchy as their fair values are estimated by using pricing models, quoted prices of securities with similar characteristics or discounted cash flows.
	Cash equivalents, restricted cash and marketable securities by security type at September 30, 2014 were as follows:
						Gross			Gross
			Amortized			Unrealized			Unrealized			Estimated
			Cost			Gains			Losses			Fair Value
			(In thousands)
	Included in cash and cash equivalents:
	Money market funds		$	5,445		$	—		$	—		$	5,445
	Restricted cash:
	Certificate of deposit		$	265		$	—		$	—		$	265
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	1,909		$	1		$	(1	)	$	1,909
	Government-sponsored enterprise securities (due in 1 to 2 years)		3,751			—			(3		)	3,748
	Commercial paper (due in less than 1 year)		12,981			18			—			12,999
	Corporate notes (due in less than 1 year)		103,927			4			(38		)	103,893
	Corporate notes (due in 1 to 2 years)		12,070			1			(18		)	12,053
			$	134,638		$	24		$	(60	)	$	134,602
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2013 were as follows:
						Gross			Gross
			Amortized			Unrealized			Unrealized			Estimated
			Cost			Gains			Losses			Fair Value
			(In thousands)
	Included in cash and cash equivalents:
	Money market funds		$	8,079		$	—		$	—		$	8,079
	Corporate notes		2,206			—			—			2,206
			$	10,285		$	—		$	—		$	10,285
	Restricted cash:
	Certificates of deposit		$	795		$	—		$	—		$	795
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	7,369		$	1		$	(1	)	$	7,369
	Commercial paper (due in less than 1 year)		5,496			3			—			5,499
	Corporate notes (due in less than 1 year)		39,383			1			(18		)	39,366
			$	52,248		$	5		$	(19	)	$	52,234
	Marketable securities with unrealized losses at September 30, 2014 and December 31, 2013 were as follows:
			Less Than 12 Months						12 Months or Greater					Total
						Gross						Gross					Gross
			Estimated			Unrealized			Estimated			Unrealized		Estimated			Unrealized
			Fair Value			Losses			Fair Value			Losses		Fair Value			Losses
			(In thousands)
	As of September 30, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401		$	(1	)	$	—		$	—	$	401		$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		3,748			(3		)	—			—		3,748			(3		)
	Corporate notes (due in less than 1 year)		77,087			(38		)	—			—		77,087			(38		)
	Corporate notes (due in 1 to 2 years)		11,222			(18		)	—			—		11,222			(18		)
			$	92,458		$	(60	)	$	—		$	—	$	92,458		$	(60	)
			Less Than 12 Months						12 Months or Greater					Total
						Gross						Gross					Gross
			Estimated			Unrealized			Estimated			Unrealized		Estimated			Unrealized
			Fair Value			Losses			Fair Value			Losses		Fair Value			Losses
	As of December 31, 2013:
	Government-sponsored enterprise securities (due in less than 1 year)		$	3,947		$	(1	)	$	—		$	—	$	3,947		$	(1	)
	Corporate notes (due in less than 1 year)		37,060			(18		)	—			—		37,060			(18		)
			$	41,007		$	(19	)	$	—		$	—	$	41,007		$	(19	)
	The gross unrealized losses related to government-sponsored enterprise securities and corporate notes as of September 30, 2014 and December 31, 2013 were due to changes in interest rates. We determined that the gross unrealized losses on our marketable securities as of September 30, 2014 and December 31, 2013 were temporary in nature. We review our investments quarterly to identify and evaluate whether any investments have indications of possible impairment. Factors considered in determining whether a loss is temporary include the length of time and extent to which the fair value has been less than the amortized cost basis and whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. We currently do not intend to sell these securities before recovery of their amortized cost basis.
	Derivatives
	Non-employee options are normally traded less actively, have trade activity that is one way, and/or are traded in less-developed markets and are therefore valued based upon models with significant unobservable market parameters, resulting in Level 3 categorization.
Options held by non-employees whose performance obligations are complete are classified as derivative liabilities on our condensed balance sheets. Upon the exercise of these options, the instruments are marked to fair value and reclassified from derivative liabilities to stockholders’ equity. We have not reclassified any derivative liabilities to stockholders’ equity for any non-employee option exercises during the nine months ended September 30, 2014.
As of September 30, 2014 and December 31, 2013, the following non-employee options to purchase common stock were considered derivatives and classified as current liabilities:
									September 30, 2014				December 31, 2013
Issuance		Exercise			Exercisable		Expiration		Number		Fair Value		Number		Fair Value
Date		Price			Date		Date		of Shares		(In thousands)		of Shares		(In thousands)
March 2005		$	6.39		January 2007		March 2015		284,600		$	1	284,600		$	367
The fair value of derivatives has been calculated at each reporting date using the Black Scholes option-pricing model with the following assumptions:
		September 30, 2014		December 31, 2013
Dividend yield		0%		0%
Expected volatility		0.635		0.844
Risk-free interest rate		0.03%		0.13%
Expected term		0.5 yr		1 yr
Dividend yield is based on historical cash dividend payments. The expected volatility is based on historical volatilities of our stock since trading volume of Geron options is limited. The risk-free interest rate is based on the U.S. Zero Coupon Treasury Strip Yields for the expected term of the derivatives in effect on the reporting date. The expected term of derivatives is equal to the remaining contractual term of the instruments.
Fair Value on a Recurring Basis
The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of September 30, 2014 and indicates the fair value category assigned.
		Fair Value Measurements at Reporting Date Using
		Quoted Prices in			Significant
		Active Markets			Other			Significant
		for Identical			Observable			Unobservable
		Assets / Liabilities			Inputs			Inputs
(In thousands)		Level 1			Level 2			Level 3			Total
Assets
Money market funds (1)		$	5,445		$	—		$	—		$	5,445
Government-sponsored enterprise securities (2)(3)		—			5,657			—			5,657
Commercial paper (2)		—			12,999			—			12,999
Corporate notes (2)(3)		—			115,946			—			115,946
Total		$	5,445		$	134,602		$	—		$	140,047
Liabilities
Derivatives (4)		$	—		$	—		$	1		$	1
The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2013 and indicates the fair value category assigned.
		Fair Value Measurements at Reporting Date Using
		Quoted Prices in			Significant
		Active Markets			Other			Significant
		for Identical			Observable			Unobservable
		Assets / Liabilities			Inputs			Inputs
(In thousands)		Level 1			Level 2			Level 3			Total
Assets
Money market funds (1)		$	8,079		$	—		$	—		$	8,079
Government-sponsored enterprise securities (2)		—			7,369			—			7,369
Commercial paper (2)		—			5,499			—			5,499
Corporate notes (1)(2)		—			41,572			—			41,572
Total		$	8,079		$	54,440		$	—		$	62,519
Liabilities
Derivatives (4)		$	—		$	—		$	367		$	367
	-1		Included in cash and cash equivalents on our condensed balance sheets.
	-2		Included in current portion of marketable securities on our condensed balance sheets.
	-3		Included in noncurrent portion of marketable securities on our condensed balance sheets.
	-4		Included in fair value of derivatives on our condensed balance sheets.
Changes in Level 3 Recurring Fair Value Measurements
The table below includes a rollforward of the balance sheet amounts for the three and nine months ended September 30, 2014, including the change in fair value, for financial instruments in the Level 3 category. When a determination is made to classify a financial instrument within Level 3, the determination is based upon the significance of the unobservable parameters to the overall fair value measurement. However, Level 3 financial instruments typically include, in addition to the unobservable components, observable components (that is, components that are actively quoted and can be validated to external sources). Accordingly, the gains and losses in the table below include changes in fair value due in part to observable factors that are part of the methodology.
					Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
					Three Months Ended September 30, 2014
																			Change in
																			Unrealized Gain
					Total														Related to
					Unrealized								Transfers						Financial
		Fair Value at			Gain			Purchases					In and/or			Fair Value at			Instruments
		June 30,			Included in			and			Sales and		Out of			September 30,			Held at
(In thousands)		2014			Earnings (1)			Issuances			Settlements		Level 3			2014			September 30, 2014 (1)
Derivative liabilities		$	290		$	(289	)	$	—		$	—	$	—		$	1		$	(289	)
					Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
					Nine Months Ended September 30, 2014
																			Change in
																			Unrealized Gain
					Total														Related to
					Unrealized								Transfers						Financial
		Fair Value at			Gain			Purchases					In and/or			Fair Value at			Instruments
		December 31,			Included in			and			Sales and		Out of			September 30,			Held at
(In thousands)		2013			Earnings (1)			Issuances			Settlements		Level 3			2014			September 30, 2014 (1)
Derivative liabilities		$	367		$	(366	)	$	—		$	—	$	—		$	1		$	(366	)
	-1		Reported as unrealized gain on derivatives on our condensed statements of operations.

DIVESTITURE_OF_STEM_CELL_ASSET

DIVESTITURE OF STEM CELL ASSETS	9 Months Ended
	Sep. 30, 2014
DIVESTITURE OF STEM CELL ASSETS	'
DIVESTITURE OF STEM CELL ASSETS	'
	3. DIVESTITURE OF STEM CELL ASSETS
	On October 1, 2013, we closed the transaction to divest our human embryonic stem cell assets and our autologous cellular immunotherapy program pursuant to the terms of the previously disclosed asset contribution agreement, or the Contribution Agreement, that we entered into in January 2013 with BioTime, Inc., or BioTime, and BioTime’s subsidiary, Asterias Biotherapeutics, Inc., or Asterias (formerly known as BioTime Acquisition Corporation).
	In accordance with the terms of the Contribution Agreement, on October 1, 2013 we received 6,537,779 shares of Asterias Series A common stock representing 21.4% of Asterias’ outstanding common stock as a class as of that date. In accordance with our contractual obligations under the Contribution Agreement, we distributed all of the shares of Asterias Series A common stock to our stockholders on a pro rata basis, other than with respect to fractional shares and shares that would otherwise have been distributed to Geron stockholders residing in certain excluded jurisdictions, which shares, as required by the Contribution Agreement, were sold with the net cash proceeds therefrom distributed ratably to the stockholders who would otherwise have been entitled to receive such shares. We refer to the distribution by us of the Asterias Series A common stock, or cash in lieu thereof, as the Series A Distribution. We completed the Series A Distribution to eligible stockholders on August 15, 2014. As of September 30, 2014, we have no remaining obligations for the Series A Distribution.
	We applied the equity method of accounting to our investment in Asterias Series A common stock. Asterias incurred net losses from October 1, 2013 through August 15, 2014. Since our investment in Asterias had an initial carrying amount of zero upon the closing of the transactions contemplated by the Contribution Agreement on October 1, 2013 and we had no commitments to provide financial support or obligations to perform services or other activities for Asterias, we suspended the equity method of accounting on October 1, 2013. Accordingly, the completion of the Series A Distribution had no impact on our condensed financial statements.

RESTRUCTURING

RESTRUCTURING	9 Months Ended
	Sep. 30, 2014
RESTRUCTURING	'
RESTRUCTURING	'
	4. RESTRUCTURING
	On April 25, 2013, we announced the decision to discontinue our discovery research programs and companion diagnostics program based on telomere length and close our research laboratory facility located at 200 Constitution Drive, Menlo Park, California. With this decision, a total of 20 positions were eliminated. In connection with this restructuring, we incurred aggregate restructuring charges of $1,370,000 for the year ended December 31, 2013, of which $940,000 was recorded during the nine months ended September 30, 2013. As of September 30, 2013, the restructuring charges recognized under the April 2013 restructuring included $624,000 related to one-time termination benefits, including $28,000 of non-cash stock-based compensation expense relating to the extension of the post-termination exercise period through the end of December 2013 for certain stock options previously granted to terminated employees, $200,000 related to non-cash charges for write-downs of excess equipment and leasehold improvements and $116,000 related to costs associated with the closure of our research laboratory facility. The remaining restructuring charges related to costs associated with the closure of our research laboratory facility and were recorded in the fourth quarter of 2013. All actions associated with this restructuring were completed in 2013, and we do not anticipate incurring any further charges in connection with this restructuring.
	The components of the accrued restructuring charges relating to the April 2013 restructuring are summarized in the following table. As of September 30, 2014, we have no remaining obligations under the April 2013 restructuring.
	(In thousands)	Employee			Facility Related			Total
		Severance and			Charges
		Other Benefits
	Beginning accrual balance as of December 31, 2013	$	21		$	73		$	94
	Cash payments	(19		)	(73		)	(92		)
	Adjustments or non-cash credits	(2		)	—			(2		)
	Ending accrual balance as of September 30, 2014	$	—		$	—		$	—

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2014
COMMITMENTS AND CONTINGENCIES.	'
COMMITMENTS AND CONTINGENCIES	'
	5. COMMITMENTS AND CONTINGENCIES
	Purported Securities and Derivative Lawsuits
	On March 14, 2014, a purported securities class action lawsuit was commenced in the United States District Court for the Northern District of California, or the California District Court, naming as defendants us and certain of our officers. The lawsuit alleges violations of the Securities Exchange Act of 1934 in connection with allegedly false and misleading statements made by us related to our Phase 2 trial of imetelstat in patients with essential thrombocythemia, or ET, or polycythemia vera, or PV. The plaintiff alleges, among other things, that we failed to disclose facts related to the occurrence of persistent low-grade liver function test, or LFT, abnormalities observed in our Phase 2 trial of imetelstat in ET or PV patients and the potential risk of chronic liver injury following long-term exposure to imetelstat. The plaintiff seeks damages and an award of reasonable costs and expenses, including attorneys’ fees. On March 28, 2014, a second purported securities class action lawsuit was commenced in the California District Court, and on June 6, 2014, a third purported securities lawsuit, not styled as a class action, was commenced in the United States District Court for the Southern District of Mississippi, or the Mississippi District Court, naming as defendants us and certain of our officers. These lawsuits, which are based on the same factual background as the purported securities class action lawsuit that commenced on March 14, 2014, also allege violations of the Securities Exchange Act of 1934 and seek damages and an award of reasonable costs and expenses, including attorneys’ fees. On June 30, 2014, the California District Court consolidated both of the purported class actions filed in the California District Court and appointed a lead plaintiff and lead counsel to represent the purported class. On July 21, 2014, the California District Court ordered the lead plaintiff to file its consolidated amended complaint, which was filed on September 19, 2014. Our response to the consolidated amended complaint is due by November 18, 2014. On August 11, 2014, we filed a motion to transfer the purported securities lawsuit filed in the Mississippi District Court to the California District Court so it can be consolidated with the purported class action lawsuits. On November 4, 2014, the Mississippi District Court granted our motion and transferred the case to the California District Court, and we intend to seek to consolidate the transferred case with the purported class action lawsuits filed in the California District Court.
	On April 21, 2014, a stockholder purporting to act on our behalf filed a derivative lawsuit in the Superior Court of California for the County of San Mateo against certain of our officers and directors. The lawsuit alleges breaches of fiduciary duties by the defendants and other violations of law. In general, the lawsuit alleges that the defendants caused or allowed the dissemination of allegedly false and misleading statements related to our Phase 2 trial of imetelstat in patients with ET or PV. The plaintiff is seeking unspecified monetary damages and other relief, including reforms and improvements to our corporate governance and internal procedures.
	For a further discussion of these ongoing lawsuits, refer to the section entitled “Legal Proceedings” in Part II, Item 1 of this Form 10-Q. These lawsuits and any other related lawsuits are subject to inherent uncertainties, and the actual defense and disposition costs will depend upon many unknown factors. The outcome of these lawsuits is necessarily uncertain. We could be forced to expend significant resources in the defense against these and any other related lawsuits and we may not prevail. We currently are not able to estimate the possible cost to us from these lawsuits, as they are currently at an early stage, and we cannot be certain how long it may take to resolve these lawsuits or the possible amount of any damages that we may be required to pay. Such amounts could be material to our financial statements even if we prevail in the defense against these lawsuits. We have not established any reserves for any potential liability relating to these lawsuits. It is possible that we could, in the future, incur judgments or enter into settlements of claims for monetary damages.

STOCKHOLDERS_EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended
	Sep. 30, 2014
STOCKHOLDERS' EQUITY	'
STOCKHOLDERS' EQUITY	'
	6. STOCKHOLDERS’ EQUITY
	On February 4, 2014, we completed an underwritten public offering of 25,875,000 shares of our common stock at a public offering price of $4.00 per share, resulting in net cash proceeds of approximately $96,805,000 after deducting the underwriting discount and offering expenses payable by us.

SEGMENT_INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2014
SEGMENT INFORMATION	'
SEGMENT INFORMATION	'
	7. SEGMENT INFORMATION
	Our executive management team represents our chief decision maker. We view our operations as one segment, the discovery and development of therapeutic products for oncology. As a result, the financial information disclosed herein materially represents all of the financial information related to our principal operating segment.

CONDENSED_STATEMENTS_OF_CASH_F1

CONDENSED STATEMENTS OF CASH FLOWS DATA	9 Months Ended
	Sep. 30, 2014
CONDENSED STATEMENTS OF CASH FLOWS DATA	'
CONDENSED STATEMENTS OF CASH FLOWS DATA	'
	8. CONDENSED STATEMENTS OF CASH FLOWS DATA
	Supplemental schedule of non-cash operating and investing activities:
		Nine Months Ended September 30,
	(In thousands)	2014			2013
	Supplemental Operating Activities:
	Issuance of common stock for 401(k) matching contributions	$	313		$	839
	Reclassification of deposits to other current assets, net	—			219
	Supplemental Investing Activities:
	Net unrealized loss on marketable securities	(22		)	(52		)

SUBSEQUENT_EVENT

SUBSEQUENT EVENT	9 Months Ended
	Sep. 30, 2014
SUBSEQUENT EVENT.	'
SUBSEQUENT EVENT	'
	9. SUBSEQUENT EVENT
	Removal of Full Clinical Hold on Imetelstat IND
	Effective October 31, 2014 the U.S. Food and Drug Administration removed the full clinical hold on our investigational new drug application for imetelstat which enables us to resume clinical development, including initiation of new clinical trials.

SUMMARY_OF_SIGNIFICANT_ACCOUNT1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2014
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
Basis of Presentation	'
	Basis of Presentation
	The terms “Geron”, the “Company”, “we” and “us” as used in this report refer to Geron Corporation. The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management of Geron, all adjustments (consisting only of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three and nine month periods ending September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014 or any other period. These financial statements and notes should be read in conjunction with the financial statements for each of the three years ended December 31, 2013, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2013 has been derived from audited financial statements at that date.
Net Loss Per Share	'
	Net Loss Per Share
	Basic earnings (loss) per share is calculated based on the weighted average number of shares of common stock outstanding during the period. Diluted earnings (loss) per share is calculated based on the weighted average number of shares of common stock and potential dilutive securities outstanding during the period. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase common stock and are determined using the treasury stock method at an average market price during the period.
	Because we are in a net loss position, diluted loss per share excludes the effects of potential dilutive securities. Had we been in a net income position, diluted earnings per share would have included the shares used in the computation of basic net loss per share as well as an additional 1,926,886 and 138,344 shares for the three months ended September 30, 2014 and 2013, respectively, and 3,205,962 and 7,183 shares for the nine months ended September 30, 2014 and 2013, respectively, related to outstanding stock options, restricted stock awards and warrants (as determined using the treasury stock method at the estimated average market value).
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On a regular basis, management evaluates these estimates and assumptions. Actual results could differ from those estimates.
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	Cash Equivalents and Marketable Securities
	We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. We are subject to credit risk related to our cash equivalents and marketable securities. We place our cash and cash equivalents in money market funds and cash operating accounts. Our marketable securities include U.S. government-sponsored enterprise securities, commercial paper and corporate notes with original maturities ranging from five to 19 months.
	We classify our marketable securities as available-for-sale. We record available-for-sale securities at fair value with unrealized gains and losses reported in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included in interest and other income and are derived using the specific identification method for determining the cost of securities sold and have been insignificant to date. Dividend and interest income are recognized when earned and included in interest and other income in our condensed statements of operations. We recognize a charge when the declines in the fair values below the amortized cost basis of our available-for-sale securities are judged to be other-than-temporary. We consider various factors in determining whether to recognize an other-than-temporary charge, including whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. Declines in market value associated with credit losses judged as other-than-temporary result in a charge to interest and other income. Other-than-temporary charges not related to credit losses are included in accumulated other comprehensive income (loss) in stockholders’ equity. We have not recorded any other-than-temporary impairment charges on our available-for-sale securities for the three and nine months ended September 30, 2014 and 2013. See Note 2 on Fair Value Measurements.
	Non-Marketable Equity Investments
	Non-marketable equity investments in companies in which we own less than 20% of the outstanding voting stock and do not otherwise have the ability to exert significant influence over the investees are carried at cost, as adjusted for other-than-temporary impairments. We apply the equity method of accounting for non-marketable equity investments in companies in which we own more than 20% of the outstanding voting stock or otherwise have the ability to exert significant influence over the investees. Under this method, we increase (decrease) the carrying value of our investment by our proportionate share of the investee’s earnings (losses). If losses exceed the carrying value of the investment, losses are then applied against any advances to the investee, including any commitment to provide financial support, until those amounts are reduced to zero. Commitments to provide financial support include formal guarantees, implicit arrangements, reputational expectations, intercompany relationships or a consistent past history of providing financial support. The equity method is then suspended until the investee has earnings. Any proportionate share of investee earnings is first applied to the share of accumulated losses not recognized during the period the equity method was suspended. We recognize previously suspended losses to the extent additional investment is determined to represent the funding of prior losses. See Note 3 on Divestiture of Stem Cell Assets.
	Fair Value of Derivatives
	For non-employee options classified as assets or liabilities, the fair value of these instruments is recorded on the condensed balance sheet at inception and adjusted to fair value at each financial reporting date. The change in fair value of the non-employee options is recorded in the condensed statements of operations as unrealized gain (loss) on derivatives. Fair value of non-employee options is estimated using the Black Scholes option-pricing model. The non-employee options continue to be reported as an asset or liability until such time as the instruments are exercised or expire or are otherwise modified to remove the provisions which require this treatment, at which time these instruments are marked to fair value and reclassified from assets or liabilities to stockholders’ equity. For non-employee options classified as permanent equity, the fair value of the non-employee options is recorded in stockholders’ equity as of their respective vesting dates and no further adjustments are made. See Note 2 on Fair Value Measurements.
Nonmonetary Transactions	'
	Nonmonetary Transactions
	We account for nonmonetary transactions based on the fair values of the assets (or services) involved. The cost of a nonmonetary asset acquired in exchange for another nonmonetary asset is the fair value of the asset surrendered to obtain it with a gain or loss recognized on the exchange. We use the fair value of the asset received to measure the cost if it is more clearly evident than the fair value of the asset surrendered. If the fair value of neither the assets received nor the assets relinquished is determinable within reasonable limits, we use the recorded amount (or carrying value) of the nonmonetary assets relinquished to account for the exchange. Similarly, we use carrying value for an exchange of controlled assets that do not meet the definition of a business for a non-controlling non-marketable equity interest in a company with no gain or loss recognized on the exchange. See Note 3 on Divestiture of Stem Cell Assets.
Revenue Recognition	'
	Revenue Recognition
	We have entered into several license agreements with various oncology, diagnostics, research tools and biologics production companies. With certain of these agreements, we receive non-refundable license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, milestone payments, royalties on future sales of products, or any combination of these items. Upfront non-refundable signing, license or non-exclusive option fees are recognized as revenue when rights to use the intellectual property related to the license have been delivered and over the term of the agreement if we have continuing performance obligations. We recognize revenue under collaborative agreements as the related research and development costs for services are rendered. Milestone payments, which are subject to substantive contingencies, are recognized as revenue upon completion of specified milestones, representing the culmination of the earnings process, according to contract terms. Royalties are generally recognized upon receipt of the related royalty payment. Deferred revenue represents the unearned portion of research and license payments received. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash.
Restricted Cash	'
	Restricted Cash
	Restricted cash consists of funds maintained in separate certificate of deposit accounts for specified purposes. The components of restricted cash were as follows:
		September 30,			December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases	265			265
		$	265		$	795
	In the third quarter of 2014, we closed the certificate of deposit for our unused equipment line of credit upon maturity and transferred the cash proceeds to our cash operating accounts. This action also canceled the availability of the equipment line of credit.
Research and Development Expenses	'
	Research and Development Expenses
	Research and development expenses consist of expenses incurred in identifying, developing and testing product candidates resulting from our independent efforts as well as efforts associated with collaborations. These expenses include, but are not limited to, acquired in-process research and development deemed to have no alternative future use, payroll and personnel expense, lab supplies, preclinical studies, clinical trials, including support for investigator-sponsored clinical trials, raw materials to manufacture clinical trial drugs, manufacturing costs for research and clinical trial materials, sponsored research at other labs, consulting, costs to maintain technology licenses and research-related overhead. Research and development costs are expensed as incurred, including payments made under our license agreements.
	Clinical Trial Costs
	A significant component of our research and development expenses has historically been clinical trial costs. Substantial portions of our preclinical studies and all of our clinical trials have been performed by third-party contract research organizations, or CROs, and other vendors. We accrue expenses for preclinical studies performed by our vendors based on certain estimates over the term of the service period and adjust our estimates as required. We accrue expenses for clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, the number of active clinical sites and the duration for which the patients have been enrolled in the study. Pass through costs from CROs include, but are not limited to, regulatory expenses, investigator fees, lab fees, travel costs and other miscellaneous costs, including shipping and printing fees. We accrue pass through costs based on estimates of the amount of work completed for the clinical trial. We monitor patient enrollment levels and related activities to the extent possible through internal reviews, review of contractual terms and correspondence with CROs. We base our estimates on the best information available at the time. However, additional information may become available to us which would allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain.
Depreciation and Amortization	'
	Depreciation and Amortization
	We record property and equipment at cost and calculate depreciation using the straight-line method over the estimated useful lives of the assets, generally four years. Leasehold improvements are amortized over the shorter of the estimated useful life or remaining term of the lease.
Stock-Based Compensation	'
	Stock-Based Compensation
	We recognize stock-based compensation expense on a straight-line basis over the requisite service period, which is generally the vesting period. The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options, restricted stock awards and employee stock purchases for the three and nine months ended September 30, 2014 and 2013 which was allocated as follows:
		Three Months Ended September 30,					Nine Months Ended September 30,
	(In thousands)	2014			2013		2014		2013
	Research and development	$	653		$	483	$	1,932	$	1,394
	Restructuring charges	—			—		—		28
	General and administrative	1,356			739		3,820		2,034
	Stock-based compensation expense included in operating expenses	$	2,009		$	1,222	$	5,752	$	3,456
	Modifications to the post-termination exercise period of outstanding options held by certain members of our executive management team resulted in additional stock-based compensation expense of $205,000 for the three and nine months ended September 30, 2013. In addition, in connection with the April 2013 restructuring, the post-termination exercise period for certain stock options previously granted to terminated employees was extended through the end of December 2013 resulting in the recognition of $28,000 of non-cash stock-based compensation expense for the nine months ended September 30, 2013. Stock-based compensation expense resulting from these modifications has been reflected in the table above. See Note 4 on Restructuring for a further discussion of the April 2013 restructuring.
	As stock-based compensation expense recognized in our condensed statements of operations for the three and nine months ended September 30, 2014 and 2013 is based on awards ultimately expected to vest, it has been reduced for estimated forfeitures, but at a minimum, reflects the grant-date fair value of those awards that actually vested in the period. Forfeitures have been estimated at the time of grant based on historical data and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	Stock Options
	We grant options with service-based vesting under our equity plans to employees, non-employee directors and consultants. The vesting period for employee options is generally four years. The fair value of options granted during the nine months ended September 30, 2014 and 2013 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.898 to 0.922		0.742 to 0.759
	Risk-free interest rate range	1.64% to 1.92%		0.80% to 1.81%
	Expected term	5.5 yrs		6 yrs
	Employee Stock Purchase Plan
	The fair value of employees’ purchase rights during the nine months ended September 30, 2014 and 2013 has been estimated using the Black Scholes option-pricing model with the following assumptions:
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.835 to 1.666		0.506 to 1.391
	Risk-free interest rate range	0.06% to 0.15%		0.09% to 0.21%
	Expected term range	6 – 12 mos		6 – 12 mos
	Dividend yield is based on historical cash dividend payments. The expected volatility is based on historical volatilities of our stock since traded options on Geron stock do not correspond to option terms and the trading volume of options is limited. The risk-free interest rate is based on the U.S. Zero Coupon Treasury Strip Yields for the expected term in effect on the date of grant for an award. The expected term of options is derived from actual historical exercise and post-vesting cancellation data and represents the period of time that options granted are expected to be outstanding. The expected term of employees’ purchase rights is equal to the purchase period.
	Restricted Stock Awards
	We have granted restricted stock awards to employees and non-employee directors with service-based vesting schedules that generally vest annually over four years. The fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. The fair value is amortized as stock-based compensation expense over the requisite service period of the award, which is generally the vesting period, on a straight-line basis and is reduced for estimated forfeitures, as applicable.
	Non-Employee Stock-Based Awards
	For our non-employee stock-based awards, the measurement date on which the fair value of the stock-based award is calculated is equal to the earlier of (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. We recognize stock-based compensation expense for the fair value of the vested portion of non-employee awards in our condensed statements of operations.
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	In April 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2014-08, Presentation of Financial Statements and Property, Plant, and Equipment: Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 raised the threshold for a disposal of assets to qualify as a discontinued operation and requires new disclosures for both discontinued operations and disposals of individually significant components of a business that do not qualify as discontinued operations. Under the new guidance, only disposals of assets representing a strategic shift in operations that has a major effect on the entity’s operations and financial results should be presented as discontinued operations. If the disposal does qualify as a discontinued operation, the entity will be required to provide expanded disclosures, as well as disclosure of the pretax income attributable to the disposal of a significant part of an entity that does not qualify as a discontinued operation. ASU 2014-08 will be effective for us beginning January 1, 2015 and subsequent interim periods. We do not expect the adoption of ASU 2014-08 to have a material effect on our financial statements.
	In May 2014, the FASB issued Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers, or ASU 2014-09. ASU 2014-09 provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 will require an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This update creates a five-step model that requires entities to exercise judgment when considering the terms of the contract(s). The five-step model includes (i) identifying the contract(s) with the customer, (ii) identifying the separate performance obligations in the contract, (iii) determining the transaction price, (iv) allocating the transaction price to the separate performance obligations, and (v) recognizing revenue when each performance obligation is satisfied. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 will be effective for us beginning January 1, 2017 and subsequent interim periods. We have the option to apply the provisions of ASU 2014-09 either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of applying this accounting standard recognized at the date of initial application. Early adoption is not permitted. We are currently evaluating the transition method and the impact that the adoption of ASU 2014-09 will have on our financial statements.
	In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, or ASU 2014-15. ASU 2014-15 is intended to define management’s responsibility to evaluate whether there is substantial doubt about an organization’s ability to continue as a going concern and to provide related footnote disclosures. Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 provides guidance to an organization’s management, with principles and definitions that are intended to reduce diversity in the timing and content of disclosures that are commonly provided by organizations in financial statement footnotes. ASU 2014-15 is effective for us beginning December 31, 2016 and subsequent interim periods. Early adoption is permitted. We are currently in the process of evaluating the impact of adoption of ASU 2014-15 on our financial statements and related disclosures.

SUMMARY_OF_SIGNIFICANT_ACCOUNT2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2014
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
Schedule of components of restricted cash	'
		September 30,			December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases	265			265
		$	265		$	795
Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards	'
		Three Months Ended September 30,					Nine Months Ended September 30,
	(In thousands)	2014			2013		2014		2013
	Research and development	$	653		$	483	$	1,932	$	1,394
	Restructuring charges	—			—		—		28
	General and administrative	1,356			739		3,820		2,034
	Stock-based compensation expense included in operating expenses	$	2,009		$	1,222	$	5,752	$	3,456
Schedule of assumptions used to estimate the fair value of stock options granted	'
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.898 to 0.922		0.742 to 0.759
	Risk-free interest rate range	1.64% to 1.92%		0.80% to 1.81%
	Expected term	5.5 yrs		6 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the Purchase Plan	'
		Nine Months Ended September 30,
		2014		2013
	Dividend yield	0%		0%
	Expected volatility range	0.835 to 1.666		0.506 to 1.391
	Risk-free interest rate range	0.06% to 0.15%		0.09% to 0.21%
	Expected term range	6 – 12 mos		6 – 12 mos

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2014
FAIR VALUE MEASUREMENTS	'
Schedule of cash equivalents, restricted cash and marketable securities by security type	'
	Cash equivalents, restricted cash and marketable securities by security type at September 30, 2014 were as follows:
						Gross			Gross
			Amortized			Unrealized			Unrealized			Estimated
			Cost			Gains			Losses			Fair Value
			(In thousands)
	Included in cash and cash equivalents:
	Money market funds		$	5,445		$	—		$	—		$	5,445
	Restricted cash:
	Certificate of deposit		$	265		$	—		$	—		$	265
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	1,909		$	1		$	(1	)	$	1,909
	Government-sponsored enterprise securities (due in 1 to 2 years)		3,751			—			(3		)	3,748
	Commercial paper (due in less than 1 year)		12,981			18			—			12,999
	Corporate notes (due in less than 1 year)		103,927			4			(38		)	103,893
	Corporate notes (due in 1 to 2 years)		12,070			1			(18		)	12,053
			$	134,638		$	24		$	(60	)	$	134,602
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2013 were as follows:
						Gross			Gross
			Amortized			Unrealized			Unrealized			Estimated
			Cost			Gains			Losses			Fair Value
			(In thousands)
	Included in cash and cash equivalents:
	Money market funds		$	8,079		$	—		$	—		$	8,079
	Corporate notes		2,206			—			—			2,206
			$	10,285		$	—		$	—		$	10,285
	Restricted cash:
	Certificates of deposit		$	795		$	—		$	—		$	795
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	7,369		$	1		$	(1	)	$	7,369
	Commercial paper (due in less than 1 year)		5,496			3			—			5,499
	Corporate notes (due in less than 1 year)		39,383			1			(18		)	39,366
			$	52,248		$	5		$	(19	)	$	52,234
Schedule of marketable securities with unrealized losses	'
			Less Than 12 Months						12 Months or Greater					Total
						Gross						Gross					Gross
			Estimated			Unrealized			Estimated			Unrealized		Estimated			Unrealized
			Fair Value			Losses			Fair Value			Losses		Fair Value			Losses
			(In thousands)
	As of September 30, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401		$	(1	)	$	—		$	—	$	401		$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		3,748			(3		)	—			—		3,748			(3		)
	Corporate notes (due in less than 1 year)		77,087			(38		)	—			—		77,087			(38		)
	Corporate notes (due in 1 to 2 years)		11,222			(18		)	—			—		11,222			(18		)
			$	92,458		$	(60	)	$	—		$	—	$	92,458		$	(60	)
			Less Than 12 Months						12 Months or Greater					Total
						Gross						Gross					Gross
			Estimated			Unrealized			Estimated			Unrealized		Estimated			Unrealized
			Fair Value			Losses			Fair Value			Losses		Fair Value			Losses
	As of December 31, 2013:
	Government-sponsored enterprise securities (due in less than 1 year)		$	3,947		$	(1	)	$	—		$	—	$	3,947		$	(1	)
	Corporate notes (due in less than 1 year)		37,060			(18		)	—			—		37,060			(18		)
			$	41,007		$	(19	)	$	—		$	—	$	41,007		$	(19	)
Schedule of non-employee options to purchase common stock considered as derivatives and classified as current liabilities	'
										September 30, 2014				December 31, 2013
	Issuance		Exercise			Exercisable		Expiration		Number		Fair Value		Number		Fair Value
	Date		Price			Date		Date		of Shares		(In thousands)		of Shares		(In thousands)
	March 2005		$	6.39		January 2007		March 2015		284,600		$	1	284,600		$	367
Schedule of assumptions used to estimate the fair value of derivatives	'
			September 30, 2014		December 31, 2013
	Dividend yield		0%		0%
	Expected volatility		0.635		0.844
	Risk-free interest rate		0.03%		0.13%
	Expected term		0.5 yr		1 yr
Schedule of financial instruments measured at fair value on recurring basis	'
	The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of September 30, 2014 and indicates the fair value category assigned.
			Fair Value Measurements at Reporting Date Using
			Quoted Prices in			Significant
			Active Markets			Other			Significant
			for Identical			Observable			Unobservable
			Assets / Liabilities			Inputs			Inputs
	(In thousands)		Level 1			Level 2			Level 3			Total
	Assets
	Money market funds (1)		$	5,445		$	—		$	—		$	5,445
	Government-sponsored enterprise securities (2)(3)		—			5,657			—			5,657
	Commercial paper (2)		—			12,999			—			12,999
	Corporate notes (2)(3)		—			115,946			—			115,946
	Total		$	5,445		$	134,602		$	—		$	140,047
	Liabilities
	Derivatives (4)		$	—		$	—		$	1		$	1
	The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2013 and indicates the fair value category assigned.
			Fair Value Measurements at Reporting Date Using
			Quoted Prices in			Significant
			Active Markets			Other			Significant
			for Identical			Observable			Unobservable
			Assets / Liabilities			Inputs			Inputs
	(In thousands)		Level 1			Level 2			Level 3			Total
	Assets
	Money market funds (1)		$	8,079		$	—		$	—		$	8,079
	Government-sponsored enterprise securities (2)		—			7,369			—			7,369
	Commercial paper (2)		—			5,499			—			5,499
	Corporate notes (1)(2)		—			41,572			—			41,572
	Total		$	8,079		$	54,440		$	—		$	62,519
	Liabilities
	Derivatives (4)		$	—		$	—		$	367		$	367
		-1		Included in cash and cash equivalents on our condensed balance sheets.
		-2		Included in current portion of marketable securities on our condensed balance sheets.
		-3		Included in noncurrent portion of marketable securities on our condensed balance sheets.
		-4		Included in fair value of derivatives on our condensed balance sheets.
Schedule of rollforward of the balance sheet amounts for financial instruments in Level 3 category	'
						Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
						Three Months Ended September 30, 2014
																				Change in
																				Unrealized Gain
						Total														Related to
						Unrealized								Transfers						Financial
			Fair Value at			Gain			Purchases					In and/or			Fair Value at			Instruments
			June 30,			Included in			and			Sales and		Out of			September 30,			Held at
	(In thousands)		2014			Earnings (1)			Issuances			Settlements		Level 3			2014			September 30, 2014 (1)
	Derivative liabilities		$	290		$	(289	)	$	—		$	—	$	—		$	1		$	(289	)
						Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
						Nine Months Ended September 30, 2014
																				Change in
																				Unrealized Gain
						Total														Related to
						Unrealized								Transfers						Financial
			Fair Value at			Gain			Purchases					In and/or			Fair Value at			Instruments
			December 31,			Included in			and			Sales and		Out of			September 30,			Held at
	(In thousands)		2013			Earnings (1)			Issuances			Settlements		Level 3			2014			September 30, 2014 (1)
	Derivative liabilities		$	367		$	(366	)	$	—		$	—	$	—		$	1		$	(366	)
		-1		Reported as unrealized gain on derivatives on our condensed statements of operations.

RESTRUCTURING_Tables

RESTRUCTURING (Tables)	9 Months Ended
	Sep. 30, 2014
RESTRUCTURING	'
Summary of components of accrued restructuring charges	'
	(In thousands)	Employee			Facility Related			Total
		Severance and			Charges
		Other Benefits
	Beginning accrual balance as of December 31, 2013	$	21		$	73		$	94
	Cash payments	(19		)	(73		)	(92		)
	Adjustments or non-cash credits	(2		)	—			(2		)
	Ending accrual balance as of September 30, 2014	$	—		$	—		$	—

CONDENSED_STATEMENTS_OF_CASH_F2

CONDENSED STATEMENTS OF CASH FLOWS DATA (Tables)	9 Months Ended
	Sep. 30, 2014
CONDENSED STATEMENTS OF CASH FLOWS DATA	'
Supplemental schedule of non-cash operating and investing activities	'
		Nine Months Ended September 30,
	(In thousands)	2014			2013
	Supplemental Operating Activities:
	Issuance of common stock for 401(k) matching contributions	$	313		$	839
	Reclassification of deposits to other current assets, net	—			219
	Supplemental Investing Activities:
	Net unrealized loss on marketable securities	(22		)	(52		)

SUMMARY_OF_SIGNIFICANT_ACCOUNT3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Loss Per Share	'	'	'	'
Potential dilutive securities excluded from diluted loss per share calculation (in shares)	1,926,886	138,344	3,205,962	7,183
Minimum	'	'	'	'
Marketable securities	'	'	'	'
Original maturity period of marketable securities	'	'	'5 months	'
Maximum	'	'	'	'
Marketable securities	'	'	'	'
Original maturity period of marketable securities	'	'	'19 months	'

SUMMARY_OF_SIGNIFICANT_ACCOUNT4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Restricted Cash	'	'
Carrying value of restricted cash	$265	$795
Depreciation and Amortization	'	'
Estimated useful lives of assets	'4 years	'
Certificate of deposit for unused equipment line of credit	'	'
Restricted Cash	'	'
Carrying value of restricted cash	'	530
Certificate of deposit for credit card purchases	'	'
Restricted Cash	'	'
Carrying value of restricted cash	$265	$265

SUMMARY_OF_SIGNIFICANT_ACCOUNT5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock-Based Compensation Expense	'	'	'	'
Stock-based compensation expense included in operating expenses	$2,009,000	$1,222,000	$5,752,000	$3,456,000
Stock-based compensation expense related to extension of the post-termination exercise period	'	205,000	'	205,000
April 2013 Restructuring	'	'	'	'
Stock-Based Compensation Expense	'	'	'	'
Stock-based compensation expense related to extension of the post-termination exercise period	'	'	'	28,000
Research and development	'	'	'	'
Stock-Based Compensation Expense	'	'	'	'
Stock-based compensation expense included in operating expenses	653,000	483,000	1,932,000	1,394,000
Restructuring charges	'	'	'	'
Stock-Based Compensation Expense	'	'	'	'
Stock-based compensation expense included in operating expenses	'	'	'	28,000
General and administrative	'	'	'	'
Stock-Based Compensation Expense	'	'	'	'
Stock-based compensation expense included in operating expenses	$1,356,000	$739,000	$3,820,000	$2,034,000

SUMMARY_OF_SIGNIFICANT_ACCOUNT6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock-Based Compensation	'	'	'	'
Stock-based compensation expense included in operating expenses	$2,009	$1,222	$5,752	$3,456
Employee Stock Purchase Plan	'	'	'	'
Assumptions used to estimate fair value of awards	'	'	'	'
Dividend yield (as a percent)	'	'	0.00%	0.00%
Expected volatility range, minimum (as a percent)	'	'	83.50%	50.60%
Expected volatility range, maximum (as a percent)	'	'	166.60%	139.10%
Risk-free interest rate range, minimum (as a percent)	'	'	0.06%	0.09%
Risk-free interest rate range, maximum (as a percent)	'	'	0.15%	0.21%
Employee Stock Purchase Plan | Minimum	'	'	'	'
Assumptions used to estimate fair value of awards	'	'	'	'
Expected term	'	'	'6 months	'6 months
Employee Stock Purchase Plan | Maximum	'	'	'	'
Assumptions used to estimate fair value of awards	'	'	'	'
Expected term	'	'	'12 months	'12 months
Service-based restricted stock awards	'	'	'	'
Stock-Based Compensation	'	'	'	'
Vesting period of awards	'	'	'4 years	'
Stock options	'	'	'	'
Stock-Based Compensation	'	'	'	'
Vesting period of awards	'	'	'4 years	'
Assumptions used to estimate fair value of awards	'	'	'	'
Dividend yield (as a percent)	'	'	0.00%	0.00%
Expected volatility range, minimum (as a percent)	'	'	89.80%	74.20%
Expected volatility range, maximum (as a percent)	'	'	92.20%	75.90%
Risk-free interest rate range, minimum (as a percent)	'	'	1.64%	0.80%
Risk-free interest rate range, maximum (as a percent)	'	'	1.92%	1.81%
Expected term	'	'	'5 years 6 months	'6 years

FAIR_VALUE_MEASUREMENTS_Detail

FAIR VALUE MEASUREMENTS (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Included in cash and cash equivalents	'	'
Amortized Cost	$5,445	$10,285
Estimated Fair Value	5,445	10,285
Restricted cash	'	'
Amortized Cost	265	795
Estimated Fair Value	265	795
Marketable securities	'	'
Amortized Cost	134,638	52,248
Gross Unrealized Gains	24	5
Gross Unrealized Losses	-60	-19
Estimated Fair Value	134,602	52,234
Money market funds	'	'
Included in cash and cash equivalents	'	'
Amortized Cost	5,445	8,079
Estimated Fair Value	5,445	8,079
Corporate notes	'	'
Included in cash and cash equivalents	'	'
Amortized Cost	'	2,206
Estimated Fair Value	'	2,206
Certificates of deposit	'	'
Restricted cash	'	'
Amortized Cost	265	795
Estimated Fair Value	265	795
Government-sponsored enterprise securities (due in less than 1 year)	'	'
Marketable securities	'	'
Amortized Cost	1,909	7,369
Gross Unrealized Gains	1	1
Gross Unrealized Losses	-1	-1
Estimated Fair Value	1,909	7,369
Government-sponsored enterprise securities (due in 1 to 2 years)	'	'
Marketable securities	'	'
Amortized Cost	3,751	'
Gross Unrealized Losses	-3	'
Estimated Fair Value	3,748	'
Commercial paper (due in less than 1 year)	'	'
Marketable securities	'	'
Amortized Cost	12,981	5,496
Gross Unrealized Gains	18	3
Estimated Fair Value	12,999	5,499
Corporate notes (due in less than 1 year)	'	'
Marketable securities	'	'
Amortized Cost	103,927	39,383
Gross Unrealized Gains	4	1
Gross Unrealized Losses	-38	-18
Estimated Fair Value	103,893	39,366
Corporate notes (due in 1 to 2 years)	'	'
Marketable securities	'	'
Amortized Cost	12,070	'
Gross Unrealized Gains	1	'
Gross Unrealized Losses	-18	'
Estimated Fair Value	$12,053	'

FAIR_VALUE_MEASUREMENTS_Detail1

FAIR VALUE MEASUREMENTS (Details 2) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Marketable securities with unrealized losses	'	'
Less Than 12 Months - Estimated Fair Value	$92,458	$41,007
Less Than 12 Months - Gross Unrealized Losses	-60	-19
Total - Estimated Fair Value	92,458	41,007
Total - Gross Unrealized Losses	-60	-19
Government-sponsored enterprise securities (due in less than 1 year)	'	'
Marketable securities with unrealized losses	'	'
Less Than 12 Months - Estimated Fair Value	401	3,947
Less Than 12 Months - Gross Unrealized Losses	-1	-1
Total - Estimated Fair Value	401	3,947
Total - Gross Unrealized Losses	-1	-1
Government-sponsored enterprise securities (due in 1 to 2 years)	'	'
Marketable securities with unrealized losses	'	'
Less Than 12 Months - Estimated Fair Value	3,748	'
Less Than 12 Months - Gross Unrealized Losses	-3	'
Total - Estimated Fair Value	3,748	'
Total - Gross Unrealized Losses	-3	'
Corporate notes (due in less than 1 year)	'	'
Marketable securities with unrealized losses	'	'
Less Than 12 Months - Estimated Fair Value	77,087	37,060
Less Than 12 Months - Gross Unrealized Losses	-38	-18
Total - Estimated Fair Value	77,087	37,060
Total - Gross Unrealized Losses	-38	-18
Corporate notes (due in 1 to 2 years)	'	'
Marketable securities with unrealized losses	'	'
Less Than 12 Months - Estimated Fair Value	11,222	'
Less Than 12 Months - Gross Unrealized Losses	-18	'
Total - Estimated Fair Value	11,222	'
Total - Gross Unrealized Losses	($18)	'

FAIR_VALUE_MEASUREMENTS_Detail2

FAIR VALUE MEASUREMENTS (Details 3) (USD $)	9 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives	'	'
Fair Value	$1	$367
Dividend yield (as a percent)	0.00%	0.00%
Expected volatility (as a percent)	63.50%	84.40%
Risk-free interest rate (as a percent)	0.03%	0.13%
Expected term	'6 months	'1 year
Non-employee options	'	'
Derivatives	'	'
Exercise Price (in dollars per share)	$6.39	'
Number of Shares	284,600	284,600
Fair Value	$1	$367

FAIR_VALUE_MEASUREMENTS_Detail3

FAIR VALUE MEASUREMENTS (Details 4) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities	'	'
Derivatives	$1	$367
Recurring basis | Level 1	'	'
Assets	'	'
Total	5,445	8,079
Recurring basis | Level 1 | Money market funds	'	'
Assets	'	'
Total	5,445	8,079
Recurring basis | Level 2	'	'
Assets	'	'
Total	134,602	54,440
Recurring basis | Level 2 | Government-sponsored enterprise securities	'	'
Assets	'	'
Total	5,657	7,369
Recurring basis | Level 2 | Commercial paper	'	'
Assets	'	'
Total	12,999	5,499
Recurring basis | Level 2 | Corporate notes	'	'
Assets	'	'
Total	115,946	41,572
Recurring basis | Level 3	'	'
Liabilities	'	'
Derivatives	1	367
Recurring basis | Total	'	'
Assets	'	'
Total	140,047	62,519
Liabilities	'	'
Derivatives	1	367
Recurring basis | Total | Money market funds	'	'
Assets	'	'
Total	5,445	8,079
Recurring basis | Total | Government-sponsored enterprise securities	'	'
Assets	'	'
Total	5,657	7,369
Recurring basis | Total | Commercial paper	'	'
Assets	'	'
Total	12,999	5,499
Recurring basis | Total | Corporate notes	'	'
Assets	'	'
Total	$115,946	$41,572

FAIR_VALUE_MEASUREMENTS_Detail4

FAIR VALUE MEASUREMENTS (Details 5) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2014
In Thousands, unless otherwise specified			Derivative liabilities	Derivative liabilities
Changes in Level 3 Recurring Fair Value Measurements	'	'	'	'
Fair value of derivative liabilities at the beginning of the period	$1	$367	$290	$367
Total Unrealized Gain Included in Earnings	'	'	-289	-366
Fair value of derivative liabilities at the end of the period	1	367	1	1
Change in Unrealized Gain Related to Financial Instruments Held at the end of the period	'	'	($289)	($366)

DIVESTITURE_OF_STEM_CELL_ASSET1

DIVESTITURE OF STEM CELL ASSETS (Details) (USD $)	0 Months Ended
	Oct. 01, 2013
Series A common stock	'
DIVESTITURE OF STEM CELL ASSETS	'
Carrying value of common stock	0
Contribution Agreement | Asterias	'
DIVESTITURE OF STEM CELL ASSETS	'
Shares issued	6,537,779
Percentage ownership in Asterias	21.40%

RESTRUCTURING_Details

RESTRUCTURING (Details) (USD $)	3 Months Ended	9 Months Ended					12 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Apr. 25, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013
				Employee Severance And Other Benefits	Facility Related Charges	April 2013 Restructuring	April 2013 Restructuring	April 2013 Restructuring	April 2013 Restructuring	April 2013 Restructuring	April 2013 Restructuring
								position	Facility Related Charges	One-time termination benefits	Asset Write Downs
RESTRUCTURING	'	'	'	'	'	'	'	'	'	'	'
Number of positions eliminated, inception to date	'	'	'	'	'	'	'	20	'	'	'
Restructuring charges	$116,000	'	$1,032,000	'	'	$940,000	$1,370,000	'	$116,000	$624,000	$200,000
Stock-based compensation expense related to extension of the post-termination exercise period	205,000	'	205,000	'	'	28,000	'	'	'	28,000	'
Outstanding restructuring liability	'	'	'	'	'	'	'	'	'	'	'
Accrual balance at the beginning of the period	'	94,000	'	21,000	73,000	'	'	'	'	'	'
Cash payments	'	-92,000	'	-19,000	-73,000	'	'	'	'	'	'
Adjustments or non-cash credits	'	($2,000)	'	($2,000)	'	'	'	'	'	'	'

STOCKHOLDERS_EQUITY_Details

STOCKHOLDERS' EQUITY (Details) (USD $)	0 Months Ended
	Feb. 04, 2014	Feb. 04, 2014
STOCKHOLDERS' EQUITY	'	'
Underwritten public offering (in shares)	25,875,000	'
Public offering price (in dollars per share)	'	$4
Net cash proceeds from public offering after deducting the underwriting discount and offering expenses	$96,805,000	'

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details)	9 Months Ended
	Sep. 30, 2014
	item
SEGMENT INFORMATION	'
Number of operating segments	1

CONDENSED_STATEMENTS_OF_CASH_F3

CONDENSED STATEMENTS OF CASH FLOWS DATA (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Supplemental Operating Activities:	'	'
Issuance of common stock for 401(k) matching contributions	$313	$839
Reclassification between deposits and other current assets	'	219
Supplemental Investing Activities:	'	'
Net unrealized loss on marketable securities	($22)	($52)