Geron (GERN) 10-Q 7 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document and Entity Information
Entity Registrant Name	GERON CORP
Entity Central Index Key	886744
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		158,087,513
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1

CONDENSED_BALANCE_SHEETS

CONDENSED BALANCE SHEETS (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$10,182	$42,796
Restricted cash	266	266
Marketable securities	135,655	108,645
Interest and other receivables	1,190	963
Prepaid assets	604	736
Total current assets	147,897	153,406
Noncurrent marketable securities	17,739	18,932
Property and equipment, net	171	173
Total assets	165,807	172,511
Current liabilities:
Accounts payable	1,180	1,033
Accrued compensation and benefits	2,135	4,213
Accrued collaboration charges	626
Accrued restructuring charges	316
Accrued liabilities	1,375	1,537
Deferred revenue	35,000	35,000
Fair value of derivatives		16
Total current liabilities	40,632	41,799
Commitments and contingencies
Stockholders' equity:
Common stock	158	157
Additional paid-in capital	1,062,782	1,059,072
Accumulated deficit	-937,748	-928,433
Accumulated other comprehensive loss	-17	-84
Total stockholders' equity	125,175	130,712
Total liabilities and stockholders' equity	$165,807	$172,511

CONDENSED_STATEMENTS_OF_OPERAT

CONDENSED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues:
License fees and royalties	$537	$474
Operating expenses:
Research and development	4,987	5,211
Restructuring charges	406
General and administrative	4,600	3,994
Total operating expenses	9,993	9,205
Loss from operations	-9,456	-8,731
Unrealized gain on derivatives	16	224
Interest and other income	149	83
Interest and other expense	-24	-16
Net loss	($9,315)	($8,440)
Basic and diluted net loss per share (in dollars per share)	($0.06)	($0.06)
Shares used in computing basic and diluted net loss per share (in shares)	157,547,568	143,465,818

CONDENSED_STATEMENTS_OF_COMPRE

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CONDENSED STATEMENTS OF COMPREHENSIVE LOSS
Net loss	($9,315)	($8,440)
Net unrealized gain (loss) on marketable securities	67	-76
Comprehensive loss	($9,248)	($8,516)

CONDENSED_STATEMENTS_OF_CASH_F

CONDENSED STATEMENTS OF CASH FLOWS CHANGE IN CASH AND CASH EQUIVALENTS (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net loss	($9,315)	($8,440)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	9	15
Accretion and amortization on investments, net	629	606
Stock-based compensation for services by non-employees	67	65
Stock-based compensation for employees and directors	2,013	1,641
Amortization related to 401(k) contributions	154	12
Unrealized gain on derivatives	-16	-224
Changes in assets and liabilities:
Other current and noncurrent assets	-95	-646
Other current liabilities	-1,151	-2,534
Net cash used in operating activities	-7,705	-9,505
Cash flows from investing activities:
Purchases of property and equipment	-7
Purchases of marketable securities	-78,869	-107,144
Proceeds from maturities of marketable securities	52,490	17,363
Net cash used in investing activities	-26,386	-89,781
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	1,477	97,620
Net cash provided by financing activities	1,477	97,620
Net decrease in cash and cash equivalents	-32,614	-1,666
Cash and cash equivalents at the beginning of the period	42,796	12,990
Cash and cash equivalents at the end of the period	$10,182	$11,324

SUMMARY_OF_SIGNIFICANT_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2015
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, or GAAP, 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 month period ending March 31, 2015 are not necessarily indicative of the results that may be expected for the year ending December 31, 2015 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, 2014, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2014 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 4,122,123 and 5,596,655 shares for the three months ended March 31, 2015 and 2014, 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 four to 20 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 months ended March 31, 2015 and 2014. See Note 2 on Fair Value Measurements.
	Fair Value of Derivatives
	For non-employee options classified as 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 a 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 liabilities to stockholders’ equity. As of March 31, 2015, all non-employee options classified as liabilities expired unexercised. 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.
	Revenue Recognition
	In general, we recognize revenue for each unit of accounting when all of the following criteria have been met: (a) persuasive evidence of an arrangement exists, (b) delivery has occurred or services have been rendered, (c) the seller’s price to the buyer is fixed or determinable, and (d) collectability is reasonably assured. Amounts received prior to satisfying these revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as noncurrent deferred revenue.
	License and/or Collaboration Agreements
	In addition to the exclusive collaboration and license agreement, or Collaboration Agreement, that we entered into with Janssen Biotech, Inc., or Janssen, in November 2014 (which is more fully described in Note 3 on Collaboration and License Agreement), we have entered into several license or collaboration agreements with various oncology, diagnostics, research tools and biologics production companies. Economic terms in these agreements may include non-refundable license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, cost-sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. In applying the appropriate revenue recognition guidance related to these agreements, we first assess whether the arrangement contains multiple elements. In this evaluation, we consider: (1) the deliverables included in the arrangement and (2) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires us to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in our control. In assessing whether an item has standalone value, we consider factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s).
	Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. We then apply the applicable revenue recognition criteria noted above to each of the separate units of accounting in determining the appropriate period and pattern of recognition. We determine how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under relevant accounting guidance. The estimated fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor-specific-objective evidence and third-party evidence are not available.
	Upfront non-refundable signing, license or non-exclusive option fees are recognized as revenue: (i) when rights to use the intellectual property, related to a license that has standalone value from the other deliverables to be provided under the agreement, have been delivered or (ii) over the term of the agreement if we have continuing performance obligations as the arrangement would be accounted for as a single unit of accounting. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash.
	At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. We consider various factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestone payments for milestones that are considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestone payments for milestones that are not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met.
	Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured. If royalties cannot be reasonably estimated or collectability of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments is accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.
	Cost-sharing expenses are recorded as earned or owed based on the performance requirements by both parties under the respective contracts. For arrangements in which we and our collaboration partner in the agreement are exposed to significant risks and rewards depending on the commercial success of the activity, we recognize payments between the parties on a net basis and record such amounts as a reduction or addition to research and development expense. For arrangements in which we have agreed to perform certain research and development services for our collaboration partner and are not exposed to significant risks and rewards depending on the commercial success of the activity, we recognize the respective cost reimbursements as revenue under the collaborative agreement as the related research and development services are rendered.
	Restricted Cash
	Restricted cash consists of funds maintained in a separate certificate of deposit account for credit card purchases.
	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, in-process research and development acquired in an asset acquisition and 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, our proportionate share of research and development costs under cost-sharing arrangements with collaborators 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 our clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For our 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 months ended March 31, 2015 and 2014 which was allocated as follows:
		Three Months Ended March 31,
	(In thousands)	2015			2014
	Research and development	$	622		$	589
	Restructuring charges	90			—
	General and administrative	1,301			1,052
	Stock-based compensation expense included in operating expenses	$	2,013		$	1,641
	In connection with a restructuring we announced in March 2015, the post-termination exercise period for certain stock options previously granted to employees affected by the restructuring was extended from 90 days to one year from their respective termination dates, subject to each employee’s continuous service until his/her specified termination date. The incremental value associated with these stock option modifications is being recognized as non-cash stock-based compensation expense over each employee’s remaining service period with the Company and recorded as restructuring charges on our condensed statements of operations as reflected in the table above. See Note 4 on Restructuring for a further discussion of the March 2015 restructuring.
	As stock-based compensation expense recognized in our condensed statements of operations for the three months ended March 31, 2015 and 2014 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 three months ended March 31, 2015 and 2014 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility	0.884		0.922
	Risk-free interest rate range	1.70%		1.64% to 1.92%
	Expected term	5.5 yrs		5.5 yrs
	Employee Stock Purchase Plan
	The fair value of employees’ purchase rights during the three months ended March 31, 2015 and 2014 has been estimated using the Black Scholes option-pricing model with the following assumptions:
		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility range	0.721 to 1.392		0.835 to 1.062
	Risk-free interest rate range	0.11% to 0.25%		0.09% to 0.15%
	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 January 2015, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2015-01, Income Statement - Extraordinary and Unusual Items (Subtopic 225-20): Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items, or ASU 2015-01. ASU 2015-01 eliminates the concept of an extraordinary item from GAAP. As a result, an entity will no longer be required to segregate extraordinary items from the results of ordinary operations to separately present an extraordinary item on its income statement, net of tax, after income from continuing operations or to disclose income taxes and earnings-per-share data applicable to an extraordinary item. However, ASU 2015-01 will still retain the presentation and disclosure guidance for items that are unusual in nature and occur infrequently. ASU 2015-01 becomes effective for annual periods, and interim periods within those annual periods, beginning on or after December 15, 2015. Early adoption is permitted. The adoption of ASU 2015-01 is not expected to have a material impact on our financial statements.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2015
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. government-sponsored enterprise securities, commercial paper and corporate notes 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 March 31, 2015 were as follows:
					Gross			Gross
			Amortized		Unrealized			Unrealized			Estimated
	(In thousands)		Cost		Gains			Losses			Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	7,231	$	—		$	—		$	7,231
	Restricted cash:
	Certificate of deposit		$	266	$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401	$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,806		—			(1		)	5,805
	Commercial paper (due in less than 1 year)		28,963		33			—			28,996
	Corporate notes (due in less than 1 year)		106,305		10			(56		)	106,259
	Corporate notes (due in 1 to 2 years)		11,936		2			(4		)	11,934
			$	153,411	$	45		$	(62	)	$	153,394
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2014 were as follows:
					Gross			Gross
			Amortized		Unrealized			Unrealized			Estimated
	(In thousands)		Cost		Gains			Losses			Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	40,342	$	—		$	—		$	40,342
	Restricted cash:
	Certificate of deposit		$	266	$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401	$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)		6,556		—			(7		)	6,549
	Commercial paper (due in less than 1 year)		10,985		14			—			10,999
	Corporate notes (due in less than 1 year)		97,307		2			(63		)	97,246
	Corporate notes (due in l to 2 years)		12,412		—			(29		)	12,383
			$	127,661	$	16		$	(100	)	$	127,577
	Marketable securities with unrealized losses at March 31, 2015 and December 31, 2014 were as follows:
			Less Than 12 Months					12 Months or Greater					Total
					Gross						Gross				Gross
			Estimated		Unrealized			Estimated			Unrealized		Estimated		Unrealized
	(In thousands)		Fair Value		Losses			Fair Value			Losses		Fair Value		Losses
	As of March 31, 2015:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400	$	(1	)	$	—		$	—	$	400	$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,805		(1		)	—			—		5,805		(1		)
	Corporate notes (due in less than 1 year)		80,083		(56		)	—			—		80,083		(56		)
	Corporate notes (due in 1 to 2 years)		6,012		(4		)	—			—		6,012		(4		)
			$	92,300	$	(62	)	$	—		$	—	$	92,300	$	(62	)
	As of December 31, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400	$	(1	)	$	—		$	—	$	400	$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,549		(7		)	—			—		5,549		(7		)
	Corporate notes (due in less than 1 year)		92,989		(63		)	—			—		92,989		(63		)
	Corporate notes (due in 1 to 2 years)		12,383		(29		)	—			—		12,383		(29		)
			$	111,321	$	(100	)	$	—		$	—	$	111,321	$	(100	)
	The gross unrealized losses related to government-sponsored enterprise securities and corporate notes as of March 31, 2015 and December 31, 2014 were due to changes in interest rates. We determined that the gross unrealized losses on our marketable securities as of March 31, 2015 and December 31, 2014 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. These options are marked to fair value at each reporting period, and upon the exercise of these options, the instruments are marked to fair value and reclassified from derivative liabilities to stockholders’ equity. As of December 31, 2014, non-employee options to purchase 284,600 shares of our common stock at an exercise price of $6.39 per share with a fair value of $16,000 were outstanding and classified as derivative liabilities. On March 31, 2015, these non-employee options expired unexercised. Accordingly, we have not reclassified any derivative liabilities to stockholders’ equity for any non-employee option exercises during the three months ended March 31, 2015.
	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 March 31, 2015 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		Inputs			Inputs
(In thousands)		Level 1		Level 2			Level 3			Total
Assets:
Money market funds(1)		$	7,231	$	—		$	—		$	7,231
Government-sponsored enterprise securities(2)(3)		—		6,205			—			6,205
Commercial paper(2)		—		28,996			—			28,996
Corporate notes(2)(3)		—		118,193			—			118,193
Total		$	7,231	$	153,394		$	—		$	160,625
The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 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)		$	40,342	$	—		$	—		$	40,342
Government-sponsored enterprise securities(2)(3)		—		6,949			—			6,949
Commercial paper(2)		—		10,999			—			10,999
Corporate notes(2)(3)		—		109,629			—			109,629
Total		$	40,342	$	127,577		$	—		$	167,919
Liabilities:
Derivatives(4)		$	—	$	—		$	16		$	16
	-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 months ended March 31, 2015, 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 gain in the table below includes changes in fair value due in part to observable factors that are part of the methodology. As of March 31, 2015, all non-employee options classified as derivative liabilities within the Level 3 fair value category expired unexercised.
				Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
				Three Months Ended March 31, 2015
																	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		March 31,			Held at
(In thousands)		2014		Earnings(1)			Issuances			Settlements		Level 3		2015			March 31, 2015
Derivative liabilities		$	16	$	(16	)	$	—		$	—	$	—	$	—		$	—
	-1		Reported as unrealized gain on derivatives in our condensed statements of operations.

COLLABORATION_AND_LICENSE_AGRE

COLLABORATION AND LICENSE AGREEMENT	3 Months Ended
	Mar. 31, 2015
COLLABORATION AND LICENSE AGREEMENT
COLLABORATION AND LICENSE AGREEMENT
	3. COLLABORATION AND LICENSE AGREEMENT
	In November 2014, we and Janssen entered into the Collaboration Agreement to develop and commercialize imetelstat worldwide for oncology, including hematologic myeloid malignancies, and all other human therapeutic uses. Under the Collaboration Agreement, we granted to Janssen exclusive worldwide rights to develop and commercialize imetelstat for all indications, and Janssen is responsible for the development, manufacturing and commercialization of, and seeking regulatory approval for, imetelstat worldwide. Upon the early termination of the waiting periods under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, the Collaboration Agreement became effective on December 15, 2014. Upon the effectiveness of the Collaboration Agreement, we received $35,000,000 from Janssen as an upfront payment, which has been classified as deferred revenue on our condensed balance sheets as of March 31, 2015 and December 31, 2014.
	Under the Collaboration Agreement, development of imetelstat will initially proceed under a mutually agreed joint clinical development plan, or CDP, which includes two agreed upon Phase 2 studies to be pursued initially and conducted by Janssen, one in myelofibrosis, or the Initial Phase 2 MF Study, and one in myelodysplastic syndrome, or the Initial Phase 2 MDS Study. Development costs for the Initial Phase 2 MF Study and the Initial Phase 2 MDS Study will be shared between us and Janssen on a 50/50 basis. Additionally, under the terms of the Collaboration Agreement, we remain responsible for prosecuting, at Janssen’s direction, the patents licensed to Janssen at the time we entered into the Collaboration Agreement, with costs shared between us and Janssen on a 50/50 basis. The cost sharing arrangement with Janssen began in 2015. As of March 31, 2015, accrued collaboration charges of $626,000 on our condensed balance sheet represent the net amount owed to Janssen for our proportionate share of research and development costs incurred under the imetelstat collaboration during the three months ended March 31, 2015.
	Following the protocol-specified primary analysis of the Initial Phase 2 MF Study or after a certain time period after the initiation of the first Phase 3 MF study, Janssen must notify us whether it elects to maintain its license rights and continue to advance the development of imetelstat in any indication. In the event that the Initial Phase 2 MF Study has been terminated early or suspended, Janssen must instead notify us of its election by the date that is the later of 24 months from the initiation of the planned Initial Phase 2 MDS Study or 24 months from the termination of the planned Initial Phase 2 MF Study or commencement of the suspension period, as applicable.
	In the event that Janssen elects to continue to maintain its license rights and advance the development of imetelstat in any indication within the applicable timeframe set forth in the Collaboration Agreement (such election, the Continuation Election), we then would have an option, or the U.S. Opt-In Rights, to share further U.S. development and promotion costs in exchange for higher tiered royalty rates and higher future development and regulatory milestone payments if imetelstat is successfully developed and approved. If we exercise the U.S. Opt-In Rights, then we and Janssen would share U.S. development and promotion costs on a 20/80 basis (Geron 20%, Janssen 80%), we would receive a $65,000,000 milestone payment, or the Continuation Fee, at the time of the Continuation Election, and would be eligible to receive additional potential payments of up to $470,000,000 in development and regulatory milestones, up to $350,000,000 in sales milestones, and tiered royalties ranging from a mid-teens up to low twenties percentage rate on worldwide net sales of imetelstat in any countries where regulatory exclusivity exists or there are valid claims under the patent rights exclusively licensed to Janssen. In addition, if we exercise the U.S. Opt-In Rights, we then would also have a separate option, or the Co-Promotion Option, to provide 20% of the U.S. selling effort with sales force personnel, in lieu of funding 20% of U.S. promotion costs, upon regulatory approval and commercial launch of imetelstat in the United States. Such co-promotion would be conducted under a Janssen prepared promotion plan, and in accordance with a co-promotion agreement to be agreed by the parties at the time of our exercise of the Co-Promotion Option. We would be responsible for all costs associated with establishing and maintaining a sales force in any conduct of such co-promotion. All product sales would be booked by Janssen. If we do not exercise the U.S. Opt-In Rights, then all further development and promotion costs beyond the Initial Phase 2 MF Study or Initial Phase 2 MDS Study would be borne by Janssen, we would receive the $65,000,000 Continuation Fee at the time of the Continuation Election plus a $70,000,000 payment, or the Full U.S. Rights Fee, for Janssen’s retention of full U.S. rights to imetelstat, and would be eligible to receive additional potential payments of up to $415,000,000 in development and regulatory milestones, up to $350,000,000 in sales milestones, and tiered royalties ranging from a double-digit up to mid-teens percentage rate on worldwide net sales of imetelstat in any countries where regulatory exclusivity exists or there are valid claims under the patent rights exclusively licensed to Janssen.
	Under the terms of the Collaboration Agreement, we and Janssen created a joint governance structure, including joint development and steering committees and working groups, to oversee and manage worldwide regulatory, development and manufacturing work under the joint CDP and promotional activities (assuming we exercises the U.S. Opt-In Rights) for imetelstat, with Janssen responsible for the operational implementation of those activities. In addition, either of the parties may propose to the joint development committee imetelstat development for any new indications not then provided for in the joint CDP and if the parties agree such development should be conducted outside of the joint CDP, each of Geron and Janssen would be entitled to independently undertake such development at its own cost, subject to the other party’s obligation to provide reimbursement for its specified portion of the costs plus a premium for such independent development following marketing approval of imetelstat in such newly proposed indication as a result of such independent development. In the event that we do not exercise the U.S. Opt-In Rights following Janssen’s Continuation Election, the joint governance structure under the Collaboration Agreement would be dissolved, a joint oversight committee would monitor the progress of the collaboration, and we would have no further rights to conduct any independent imetelstat development.
	After a Continuation Election by Janssen, the Collaboration Agreement would remain in effect until the expiration of the last-to-expire patent or the royalty obligations on sales of imetelstat cease, unless terminated earlier. If Janssen does not effect a Continuation Election, then the Collaboration Agreement would terminate and all rights to the imetelstat program would revert to us. Janssen may terminate the Collaboration Agreement at any time for convenience and due to a safety-related concern. If a notice of termination from Janssen occurs, we would be entitled to certain continued operational support and cost-sharing under various circumstances and all rights to the imetelstat program would revert to us.
	The terms of the Collaboration Agreement contain multiple deliverables, which include at inception: (i) exclusive worldwide rights to develop and commercialize imetelstat for all indications, (ii) transfer of know-how and intellectual property, including our obligation to procure supply for manufacturing imetelstat for up to nine months after the effective date of the Collaboration Agreement, (iii) participation on the joint steering committees and working groups and (iv) potential participation in selling imetelstat in the United States, if approved for commercial sale. We concluded the license for exclusive worldwide rights to develop and commercialize imetelstat has standalone value to Janssen based on the technical and financial resources of Janssen, including Janssen’s drug development experience, sizeable employee base with specific experience in hematologic malignancies, and sufficient capital to independently develop imetelstat on a global basis. Since Janssen has final decision-making authority in the event a unanimous decision cannot be reached by the joint steering committees, we determined our participation on the joint steering committees does not represent a non-contingent deliverable under the Collaboration Agreement. In addition, we determined our potential participation in selling imetelstat in the United States does not represent a non-contingent deliverable because such participation is uncertain and dependent on the drug being approved for commercial sale, which is not within our control. Accordingly, we have determined delivery of the license rights granted by us to Janssen, together with our performance of the technology transfer-related activities, represents the sole non-contingent deliverable under the Collaboration Agreement. Therefore, we have accounted for our delivery of the license rights and our performance of the technology transfer-related activities as a single unit of accounting. We currently expect completion of the technology transfer-related activities to occur by September 30, 2015 at which point we expect to fully recognize the $35,000,000 upfront payment from Janssen as license fee revenue on our condensed statement of operations. As a result, we have not recognized any revenue related to the Collaboration Agreement for the three months ended March 31, 2015.
	We have determined that each of the additional potential milestone payments to us under the Collaboration Agreement, including: (i) the Continuation Fee at the time of the Continuation Election, (ii) the Full U.S. Rights Fee if we do not exercise the U.S. Opt-In Rights and (iii) payments based on the achievement of certain development, regulatory or commercial milestones, represent substantive milestones. Consequently, we will recognize revenue for these payments in their entirety upon successful accomplishment of the respective milestone. Royalties on future product sales of imetelstat, if successfully commercialized under the Collaboration Agreement, will be recognized as revenue when earned.

RESTRUCTURING

RESTRUCTURING	3 Months Ended
	Mar. 31, 2015
RESTRUCTURING
RESTRUCTURING
	4. RESTRUCTURING
	In light of projected reduced operational demands as a result of the Collaboration Agreement with Janssen, on March 3, 2015, we announced an organizational resizing to reduce our workforce from 39 to 21 positions. We expect the majority of the reduction in our workforce to be completed by the end of the second quarter of 2015. In connection with this restructuring, we expect to record aggregate restructuring charges of approximately $1,748,000 related to one-time termination benefits which will be recognized on a pro-rata basis commencing from the date of announcement over the specified remaining service periods for the employees affected by the restructuring. For the three months ended March 31, 2015, we recognized $406,000 in restructuring charges for the pro-rata portion of the one-time termination benefits, which included $90,000 of non-cash stock-based compensation expense relating to the extension of the post-termination exercise period for certain stock options previously granted to employees affected by the restructuring from 90 days to one year from their respective termination dates. The majority of the remaining projected restructuring charges is expected to be recorded during the second quarter of 2015. We may incur other charges associated with this restructuring. Such charges, if any, will be recorded as they are determined. We expect this restructuring to be completed in 2015 and result in aggregate cash expenditures of approximately $1,377,000, the majority of which is expected to be paid in 2015. As of March 31, 2015, we have not made any payments in connection with this restructuring.
	The components relating to the restructuring, including the outstanding restructuring liability which is included in accrued restructuring charges on our condensed balance sheet as of March 31, 2015, are summarized in the following table:
	(In thousands)	Employee Severance
		and Other Benefits
	Beginning accrual balance as of December 31, 2014	$	—
	Restructuring charges	406
	Adjustments or non-cash credits, including non-cash stock-based compensation expense	(90		)
	Ending accrual balance as of March 31, 2015	$	316

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2015
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. 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. On November 4, 2014, the Mississippi District Court granted our motion and transferred the case to the California District Court, which was thereafter consolidated with the class actions. On November 18, 2014, we filed a motion with the California District Court to dismiss the consolidated amended complaint. The plaintiff’s opposition to our motion to dismiss was filed on January 20, 2015, and we filed our reply in support of our motion to dismiss on February 25, 2015. A hearing on the motion to dismiss the consolidated amended complaint occurred on April 10, 2015. At the hearing, the California District Court granted our motion to dismiss with respect to some of the allegedly false and misleading statements made by us and denied our motion to dismiss with respect to other allegedly false and misleading statements made by us.
	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. It is possible that additional derivative lawsuits will be filed with respect to these same or other matters and also naming our officers and directors as defendants. Proceedings in the derivative lawsuit are pending further developments in the purported securities class action lawsuit. We intend to vigorously defend against the claims alleged and to seek dismissal of the lawsuit.
	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	3 Months Ended
	Mar. 31, 2015
STOCKHOLDERS' EQUITY
STOCKHOLDERS' EQUITY
	6. STOCKHOLDERS’ EQUITY
	On March 31, 2015, warrants to purchase 235,000 shares of our common stock were exercised at an exercise price of $3.75 per share. We received cash proceeds of approximately $881,000 from the exercise of these warrants.

SEGMENT_INFORMATION

SEGMENT INFORMATION	3 Months Ended
	Mar. 31, 2015
SEGMENT INFORMATION
SEGMENT INFORMATION
	7. SEGMENT INFORMATION
	Our executive management team represents our chief decision maker. We view our operations as one segment, the 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	3 Months Ended
	Mar. 31, 2015
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:
		Three Months Ended March 31,
	(In thousands)	2015		2014
	Supplemental Operating Activities:
	Issuance of common stock for 401(k) matching contributions	$	—	$	313
	Reclassification of deposits to other current assets	—		4
	Supplemental Investing Activities:
	Net unrealized gain (loss) on marketable securities	67		(76		)

SUMMARY_OF_SIGNIFICANT_ACCOUNT1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2015
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, or GAAP, 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 month period ending March 31, 2015 are not necessarily indicative of the results that may be expected for the year ending December 31, 2015 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, 2014, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2014 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 4,122,123 and 5,596,655 shares for the three months ended March 31, 2015 and 2014, 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 four to 20 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 months ended March 31, 2015 and 2014. See Note 2 on Fair Value Measurements.
	Fair Value of Derivatives
	For non-employee options classified as 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 a 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 liabilities to stockholders’ equity. As of March 31, 2015, all non-employee options classified as liabilities expired unexercised. 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.
Revenue Recognition
	Revenue Recognition
	In general, we recognize revenue for each unit of accounting when all of the following criteria have been met: (a) persuasive evidence of an arrangement exists, (b) delivery has occurred or services have been rendered, (c) the seller’s price to the buyer is fixed or determinable, and (d) collectability is reasonably assured. Amounts received prior to satisfying these revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as noncurrent deferred revenue.
	License and/or Collaboration Agreements
	In addition to the exclusive collaboration and license agreement, or Collaboration Agreement, that we entered into with Janssen Biotech, Inc., or Janssen, in November 2014 (which is more fully described in Note 3 on Collaboration and License Agreement), we have entered into several license or collaboration agreements with various oncology, diagnostics, research tools and biologics production companies. Economic terms in these agreements may include non-refundable license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, cost-sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. In applying the appropriate revenue recognition guidance related to these agreements, we first assess whether the arrangement contains multiple elements. In this evaluation, we consider: (1) the deliverables included in the arrangement and (2) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires us to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in our control. In assessing whether an item has standalone value, we consider factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s).
	Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. We then apply the applicable revenue recognition criteria noted above to each of the separate units of accounting in determining the appropriate period and pattern of recognition. We determine how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under relevant accounting guidance. The estimated fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor-specific-objective evidence and third-party evidence are not available.
	Upfront non-refundable signing, license or non-exclusive option fees are recognized as revenue: (i) when rights to use the intellectual property, related to a license that has standalone value from the other deliverables to be provided under the agreement, have been delivered or (ii) over the term of the agreement if we have continuing performance obligations as the arrangement would be accounted for as a single unit of accounting. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash.
	At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. We consider various factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestone payments for milestones that are considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestone payments for milestones that are not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met.
	Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured. If royalties cannot be reasonably estimated or collectability of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments is accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.
	Cost-sharing expenses are recorded as earned or owed based on the performance requirements by both parties under the respective contracts. For arrangements in which we and our collaboration partner in the agreement are exposed to significant risks and rewards depending on the commercial success of the activity, we recognize payments between the parties on a net basis and record such amounts as a reduction or addition to research and development expense. For arrangements in which we have agreed to perform certain research and development services for our collaboration partner and are not exposed to significant risks and rewards depending on the commercial success of the activity, we recognize the respective cost reimbursements as revenue under the collaborative agreement as the related research and development services are rendered.
Restricted Cash
	Restricted Cash
	Restricted cash consists of funds maintained in a separate certificate of deposit account for credit card purchases.
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, in-process research and development acquired in an asset acquisition and 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, our proportionate share of research and development costs under cost-sharing arrangements with collaborators 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 our clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For our 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 months ended March 31, 2015 and 2014 which was allocated as follows:
		Three Months Ended March 31,
	(In thousands)	2015			2014
	Research and development	$	622		$	589
	Restructuring charges	90			—
	General and administrative	1,301			1,052
	Stock-based compensation expense included in operating expenses	$	2,013		$	1,641
	In connection with a restructuring we announced in March 2015, the post-termination exercise period for certain stock options previously granted to employees affected by the restructuring was extended from 90 days to one year from their respective termination dates, subject to each employee’s continuous service until his/her specified termination date. The incremental value associated with these stock option modifications is being recognized as non-cash stock-based compensation expense over each employee’s remaining service period with the Company and recorded as restructuring charges on our condensed statements of operations as reflected in the table above. See Note 4 on Restructuring for a further discussion of the March 2015 restructuring.
	As stock-based compensation expense recognized in our condensed statements of operations for the three months ended March 31, 2015 and 2014 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 three months ended March 31, 2015 and 2014 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility	0.884		0.922
	Risk-free interest rate range	1.70%		1.64% to 1.92%
	Expected term	5.5 yrs		5.5 yrs
	Employee Stock Purchase Plan
	The fair value of employees’ purchase rights during the three months ended March 31, 2015 and 2014 has been estimated using the Black Scholes option-pricing model with the following assumptions:
		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility range	0.721 to 1.392		0.835 to 1.062
	Risk-free interest rate range	0.11% to 0.25%		0.09% to 0.15%
	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 January 2015, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2015-01, Income Statement - Extraordinary and Unusual Items (Subtopic 225-20): Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items, or ASU 2015-01. ASU 2015-01 eliminates the concept of an extraordinary item from GAAP. As a result, an entity will no longer be required to segregate extraordinary items from the results of ordinary operations to separately present an extraordinary item on its income statement, net of tax, after income from continuing operations or to disclose income taxes and earnings-per-share data applicable to an extraordinary item. However, ASU 2015-01 will still retain the presentation and disclosure guidance for items that are unusual in nature and occur infrequently. ASU 2015-01 becomes effective for annual periods, and interim periods within those annual periods, beginning on or after December 15, 2015. Early adoption is permitted. The adoption of ASU 2015-01 is not expected to have a material impact on our financial statements.

SUMMARY_OF_SIGNIFICANT_ACCOUNT2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2015
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
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 March 31,
	(In thousands)	2015			2014
	Research and development	$	622		$	589
	Restructuring charges	90			—
	General and administrative	1,301			1,052
	Stock-based compensation expense included in operating expenses	$	2,013		$	1,641
Schedule of assumptions used to estimate the fair value of stock options granted		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility	0.884		0.922
	Risk-free interest rate range	1.70%		1.64% to 1.92%
	Expected term	5.5 yrs		5.5 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the Purchase Plans		Three Months Ended March 31,
		2015		2014
	Dividend yield	0%		0%
	Expected volatility range	0.721 to 1.392		0.835 to 1.062
	Risk-free interest rate range	0.11% to 0.25%		0.09% to 0.15%
	Expected term range	6 – 12 mos		6 – 12 mos

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015 were as follows:
					Gross			Gross
			Amortized		Unrealized			Unrealized			Estimated
	(In thousands)		Cost		Gains			Losses			Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	7,231	$	—		$	—		$	7,231
	Restricted cash:
	Certificate of deposit		$	266	$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401	$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,806		—			(1		)	5,805
	Commercial paper (due in less than 1 year)		28,963		33			—			28,996
	Corporate notes (due in less than 1 year)		106,305		10			(56		)	106,259
	Corporate notes (due in 1 to 2 years)		11,936		2			(4		)	11,934
			$	153,411	$	45		$	(62	)	$	153,394
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2014 were as follows:
					Gross			Gross
			Amortized		Unrealized			Unrealized			Estimated
	(In thousands)		Cost		Gains			Losses			Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	40,342	$	—		$	—		$	40,342
	Restricted cash:
	Certificate of deposit		$	266	$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401	$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)		6,556		—			(7		)	6,549
	Commercial paper (due in less than 1 year)		10,985		14			—			10,999
	Corporate notes (due in less than 1 year)		97,307		2			(63		)	97,246
	Corporate notes (due in l to 2 years)		12,412		—			(29		)	12,383
			$	127,661	$	16		$	(100	)	$	127,577
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
	(In thousands)		Fair Value		Losses			Fair Value			Losses		Fair Value		Losses
	As of March 31, 2015:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400	$	(1	)	$	—		$	—	$	400	$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,805		(1		)	—			—		5,805		(1		)
	Corporate notes (due in less than 1 year)		80,083		(56		)	—			—		80,083		(56		)
	Corporate notes (due in 1 to 2 years)		6,012		(4		)	—			—		6,012		(4		)
			$	92,300	$	(62	)	$	—		$	—	$	92,300	$	(62	)
	As of December 31, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400	$	(1	)	$	—		$	—	$	400	$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)		5,549		(7		)	—			—		5,549		(7		)
	Corporate notes (due in less than 1 year)		92,989		(63		)	—			—		92,989		(63		)
	Corporate notes (due in 1 to 2 years)		12,383		(29		)	—			—		12,383		(29		)
			$	111,321	$	(100	)	$	—		$	—	$	111,321	$	(100	)
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 March 31, 2015 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		Inputs			Inputs
	(In thousands)		Level 1		Level 2			Level 3			Total
	Assets:
	Money market funds(1)		$	7,231	$	—		$	—		$	7,231
	Government-sponsored enterprise securities(2)(3)		—		6,205			—			6,205
	Commercial paper(2)		—		28,996			—			28,996
	Corporate notes(2)(3)		—		118,193			—			118,193
	Total		$	7,231	$	153,394		$	—		$	160,625
	The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 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)		$	40,342	$	—		$	—		$	40,342
	Government-sponsored enterprise securities(2)(3)		—		6,949			—			6,949
	Commercial paper(2)		—		10,999			—			10,999
	Corporate notes(2)(3)		—		109,629			—			109,629
	Total		$	40,342	$	127,577		$	—		$	167,919
	Liabilities:
	Derivatives(4)		$	—	$	—		$	16		$	16
		-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 March 31, 2015
																		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		March 31,			Held at
	(In thousands)		2014		Earnings(1)			Issuances			Settlements		Level 3		2015			March 31, 2015
	Derivative liabilities		$	16	$	(16	)	$	—		$	—	$	—	$	—		$	—
		-1		Reported as unrealized gain on derivatives in our condensed statements of operations.

RESTRUCTURING_Tables

RESTRUCTURING (Tables)	3 Months Ended
	Mar. 31, 2015
RESTRUCTURING
Summary of components of restructuring liability	(In thousands)	Employee Severance
		and Other Benefits
	Beginning accrual balance as of December 31, 2014	$	—
	Restructuring charges	406
	Adjustments or non-cash credits, including non-cash stock-based compensation expense	(90		)
	Ending accrual balance as of March 31, 2015	$	316

CONDENSED_STATEMENTS_OF_CASH_F2

CONDENSED STATEMENTS OF CASH FLOWS DATA (Tables)	3 Months Ended
	Mar. 31, 2015
CONDENSED STATEMENTS OF CASH FLOWS DATA
Supplemental schedule of non-cash operating and investing activities		Three Months Ended March 31,
	(In thousands)	2015		2014
	Supplemental Operating Activities:
	Issuance of common stock for 401(k) matching contributions	$	—	$	313
	Reclassification of deposits to other current assets	—		4
	Supplemental Investing Activities:
	Net unrealized gain (loss) on marketable securities	67		(76		)

SUMMARY_OF_SIGNIFICANT_ACCOUNT3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Net Loss Per Share
Potential dilutive securities excluded from diluted earnings (loss) per share calculation (in shares)	4,122,123	5,596,655
Depreciation and Amortization
Estimated useful lives of assets	4 years
Minimum
Marketable securities
Original maturity period of marketable securities	4 months
Maximum
Marketable securities
Original maturity period of marketable securities	20 months

SUMMARY_OF_SIGNIFICANT_ACCOUNT4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$2,013	$1,641
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	622	589
Restructuring charges
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	90
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$1,301	$1,052

SUMMARY_OF_SIGNIFICANT_ACCOUNT5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4)	0 Months Ended	3 Months Ended
	Mar. 03, 2015	Mar. 31, 2015	Mar. 31, 2014
March 2015 Restructuring
Stock-Based Compensation
Original exercise period for vested outstanding awards after termination	90 days
Modified exercise period for vested outstanding awards after termination	1 year
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)		72.10%	83.50%
Expected volatility range, maximum (as a percent)		139.20%	106.20%
Risk-free interest rate range, minimum (as a percent)		0.11%	0.09%
Risk-free interest rate range, maximum (as a percent)		0.25%	0.15%
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 (as a percent)		88.40%	92.20%
Risk-free interest rate (as a percent)		1.70%
Risk-free interest rate range, minimum (as a percent)			1.64%
Risk-free interest rate range, maximum (as a percent)			1.92%
Expected term		5 years 6 months	5 years 6 months

FAIR_VALUE_MEASUREMENTS_Detail

FAIR VALUE MEASUREMENTS (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Included in cash and cash equivalents
Amortized Cost	$7,231	$40,342
Estimated Fair Value	7,231	40,342
Restricted cash
Amortized Cost	266	266
Estimated Fair Value	266	266
Marketable securities
Amortized Cost	153,411	127,661
Gross Unrealized Gains	45	16
Gross Unrealized Losses	-62	-100
Estimated Fair Value	153,394	127,577
Money market funds
Included in cash and cash equivalents
Amortized Cost	7,231	40,342
Estimated Fair Value	7,231	40,342
Certificates of deposit
Restricted cash
Amortized Cost	266	266
Estimated Fair Value	266	266
Government-sponsored enterprise securities (due in less than 1 year)
Marketable securities
Amortized Cost	401	401
Gross Unrealized Losses	-1	-1
Estimated Fair Value	400	400
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities
Amortized Cost	5,806	6,556
Gross Unrealized Losses	-1	-7
Estimated Fair Value	5,805	6,549
Commercial paper (due in less than 1 year)
Marketable securities
Amortized Cost	28,963	10,985
Gross Unrealized Gains	33	14
Estimated Fair Value	28,996	10,999
Corporate notes (due in less than 1 year)
Marketable securities
Amortized Cost	106,305	97,307
Gross Unrealized Gains	10	2
Gross Unrealized Losses	-56	-63
Estimated Fair Value	106,259	97,246
Corporate notes (due in 1 to 2 years)
Marketable securities
Amortized Cost	11,936	12,412
Gross Unrealized Gains	2
Gross Unrealized Losses	-4	-29
Estimated Fair Value	$11,934	$12,383

FAIR_VALUE_MEASUREMENTS_Detail1

FAIR VALUE MEASUREMENTS (Details 2) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$92,300	$111,321
Less Than 12 Months - Gross Unrealized Losses	-62	-100
Total - Estimated Fair Value	92,300	111,321
Total - Gross Unrealized Losses	-62	-100
Government-sponsored enterprise securities (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	400	400
Less Than 12 Months - Gross Unrealized Losses	-1	-1
Total - Estimated Fair Value	400	400
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	5,805	5,549
Less Than 12 Months - Gross Unrealized Losses	-1	-7
Total - Estimated Fair Value	5,805	5,549
Total - Gross Unrealized Losses	-1	-7
Corporate notes (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	80,083	92,989
Less Than 12 Months - Gross Unrealized Losses	-56	-63
Total - Estimated Fair Value	80,083	92,989
Total - Gross Unrealized Losses	-56	-63
Corporate notes (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	6,012	12,383
Less Than 12 Months - Gross Unrealized Losses	-4	-29
Total - Estimated Fair Value	6,012	12,383
Total - Gross Unrealized Losses	($4)	($29)

FAIR_VALUE_MEASUREMENTS_Detail2

FAIR VALUE MEASUREMENTS (Details 3) (USD $)	Dec. 31, 2014
Derivatives
Fair Value	$16,000
Non-employee options
Derivatives
Number of Shares	284,600
Exercise Price (in dollars per share)	$6.39
Fair Value	$16,000

FAIR_VALUE_MEASUREMENTS_Detail3

FAIR VALUE MEASUREMENTS (Details 4) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Liabilities
Derivatives		$16,000
Recurring basis | Level 1
Assets
Total	7,231,000	40,342,000
Recurring basis | Level 1 | Money market funds
Assets
Total	7,231,000	40,342,000
Recurring basis | Level 2
Assets
Total	153,394,000	127,577,000
Recurring basis | Level 2 | Government-sponsored enterprise securities
Assets
Total	6,205,000	6,949,000
Recurring basis | Level 2 | Commercial paper
Assets
Total	28,996,000	10,999,000
Recurring basis | Level 2 | Corporate notes
Assets
Total	118,193,000	109,629,000
Recurring basis | Level 3
Liabilities
Derivatives		16,000
Recurring basis | Total
Assets
Total	160,625,000	167,919,000
Liabilities
Derivatives		16,000
Recurring basis | Total | Money market funds
Assets
Total	7,231,000	40,342,000
Recurring basis | Total | Government-sponsored enterprise securities
Assets
Total	6,205,000	6,949,000
Recurring basis | Total | Commercial paper
Assets
Total	28,996,000	10,999,000
Recurring basis | Total | Corporate notes
Assets
Total	$118,193,000	$109,629,000

FAIR_VALUE_MEASUREMENTS_Detail4

FAIR VALUE MEASUREMENTS (Details 5) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Changes in Level 3 Recurring Fair Value Measurements
Fair value of derivative liabilities at the beginning of the period		$16,000
Fair value of derivative liabilities at the end of the period		16,000
Derivative liabilities
Changes in Level 3 Recurring Fair Value Measurements
Fair value of derivative liabilities at the beginning of the period	16,000
Total Unrealized Gain Included in Earnings	($16,000)

COLLABORATION_AND_LICENSE_AGRE1

COLLABORATION AND LICENSE AGREEMENT (Details) (USD $)	0 Months Ended
	Dec. 15, 2014	Mar. 31, 2015	Dec. 31, 2014
	item
LICENSE AGREEMENTS
Amount expected to be recognized as revenue		$35,000,000	$35,000,000
Accrued collaboration charges		626,000
Expected Revenue
LICENSE AGREEMENTS
Amount expected to be recognized as revenue		35,000,000
License agreements | Janssen Biotech | Initial Period
LICENSE AGREEMENTS
Upfront payment received	35,000,000
Number of agreed upon studies	2
Percentage of costs to be paid by Geron	50.00%
Percentage of costs to be paid by Janssen	50.00%
Notification period	24 months
Maximum period Geron is obligated to procure supply for manufacturing imetelstat under collaboration agreement	9 months
License agreements | Janssen Biotech | U.S. Opt-In Rights exercised
LICENSE AGREEMENTS
Percentage of costs to be paid by Geron	20.00%
Percentage of costs to be paid by Janssen	80.00%
Continuation Election milestone payment	65,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement	470,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement	350,000,000
Tiered royalties percentage, low end of the range	mid-teens
Tiered royalties percentage, high end of the range	low twenties
U.S. selling effort percentage	20.00%
License agreements | Janssen Biotech | U.S. Opt-In Rights not exercised
LICENSE AGREEMENTS
Continuation Election milestone payment	65,000,000
Full U.S. Rights fee	70,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement	415,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement	$350,000,000
Tiered royalties percentage, low end of the range	double-digit
Tiered royalties percentage, high end of the range	mid-teens
License agreements | Janssen Biotech | Collaborative Arrangement IP Exclusively Licensed
LICENSE AGREEMENTS
Percentage of costs to be paid by Geron	50.00%
Percentage of costs to be paid by Janssen	50.00%

RESTRUCTURING_Details

RESTRUCTURING (Details) (USD $)	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 03, 2015
RESTRUCTURING
Restructuring charges	$406,000
Outstanding restructuring liability
Restructuring Charges.	406,000
Accrual balance at the end of the period	316,000
Employee Severance And Other Benefits
RESTRUCTURING
Restructuring charges	406,000
Stock-based compensation expense related to extension of the post-termination exercise period	-90,000
Outstanding restructuring liability
Restructuring Charges.	406,000
Stock-based compensation expense related to extension of the post-termination exercise period	-90,000
Accrual balance at the end of the period	316,000
March 2015 Restructuring
RESTRUCTURING
Number of positions before restructuring		39
Number of positions after restructuring		21
Original exercise period for vested outstanding awards after termination		90 days
Modified exercise period for vested outstanding awards after termination		1 year
Aggregate estimated restructuring charges		1,748,000
Expected cash payments		1,377,000
March 2015 Restructuring | One-time termination benefits
RESTRUCTURING
Restructuring charges	406,000
Stock-based compensation expense related to extension of the post-termination exercise period	90,000
Outstanding restructuring liability
Restructuring Charges.	406,000
Stock-based compensation expense related to extension of the post-termination exercise period	$90,000

STOCKHOLDERS_EQUITY_Details

STOCKHOLDERS' EQUITY (Details) (USD $)	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2015
STOCKHOLDERS' EQUITY
Number of warrants exercised	235,000
Exercise price of warrants issued (in dollars per share)		$3.75
Proceeds from exercise of warrants	$881,000

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details)	3 Months Ended
	Mar. 31, 2015
	item
SEGMENT INFORMATION
Number of operating segments	1

CONDENSED_STATEMENTS_OF_CASH_F3

CONDENSED STATEMENTS OF CASH FLOWS DATA (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Supplemental Operating Activities:
Issuance of common stock for 401(k) matching contributions		$313
Reclassification of deposits to other current assets		4
Supplemental Investing Activities:
Net unrealized gain (loss) on marketable securities	$67	($76)