Organization, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019. The Condensed Consolidated Balance Sheet data at December 31, 2018 was derived from the audited consolidated financial statements included in Sangamo’s Annual Report on Form 10-K for the year ended December 31, 2018 (the “2018 Annual Report”) as filed with the SEC on March 1, 2019. The accompanying Condensed Consolidated Financial Statements and related financial information should be read in conjunction with the audited financial statements and footnotes thereto for the year ended December 31, 2018, included in the 2018 Annual Report.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates including critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities, including from acquisitions, and stock-based compensation. Estimates are based on historical experience and on various other market specific and other relevant assumptions that the Company believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates. In March 2019, the Company recorded an adjustment to revenue related to a change in estimate in connection with the hemophilia A collaboration agreement with Pfizer Inc. (“Pfizer”). This adjustment was a direct result of the increase in project scope during the first quarter of 2019 and the corresponding costs which resulted in a decrease in the measure of proportional performance. This adjustment decreased revenue by $3.0 million, increased net loss by $3.0 million and increased the Company’s basic net loss per share by $0.03 for the nine months ended September 30, 2019.
Foreign Currency Translation	Foreign Currency Translation The functional currency of the Company’s foreign subsidiaries is primarily the Euro. Assets and liabilities denominated in foreign currencies are translated to U.S. dollars using the exchange rates at the balance sheet date. Foreign currency translation adjustments are recorded as a component of Accumulated Other Comprehensive Income (Loss) (“AOCI”) within stockholders’ equity. Revenues and expenses from the Company’s foreign subsidiaries are translated using the monthly average exchange rates in effect during the period in which the transactions occur. Foreign currency transaction gains and losses are recorded in interest and other income, net, on the Company’s Condensed Consolidated Statements of Operations.
Reclassifications	Reclassifications Certain prior period amounts in the accompanying Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation. These reclassifications had no effect on the reported results of operations. The Company reclassified $0.6 million from Intangible assets to Other non-current assets on the Condensed Consolidated Balance Sheet as of December 31, 2018.
Cash and Cash Equivalents	Cash and Cash Equivalents Sangamo considers all highly-liquid investments purchased with original maturities of three months or less at the purchase date to be cash equivalents. Cash and cash equivalents consist of cash, deposits in demand money market accounts and commercial paper.
Marketable Securities	Marketable Securities Sangamo classifies its marketable securities as available-for-sale and records its investments at estimated fair value based on quoted market prices or observable market inputs of almost identical assets, with the unrealized holding gains and losses included in AOCI. The Company’s investments are subject to a periodic impairment review. The Company recognizes an impairment charge, if material; when a decline in the fair value of its investments below the cost basis is judged to be other-than-temporary. The Company considers various factors in determining whether to recognize an impairment charge, including the length of time and extent to which the fair value has been less than the Company’s cost basis, the financial condition and near-term prospects of the investee and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in the market value. Realized gains and losses on available-for-sale securities are included in other income, net, which are determined using the specific identification method.
Concentrations of Risk	Concentrations of Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to a concentration of credit risk to the extent of the fair value recorded in the Condensed Consolidated Balance Sheets. The Company invests cash that is not required for immediate operating needs primarily in highly liquid instruments that bear minimal risk. The Company has established guidelines relating to the quality, diversification, and maturities of securities to enable the Company to manage its credit risk. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents and investments and issuers of investments to the extent recorded on the Condensed Consolidated Balance Sheets. Certain materials and key components that the Company utilizes in its operations are obtained through single suppliers. Since the suppliers of key components and materials must be named in an investigational new drug application filed with the U.S. Food and Drug Administration for a product, significant delays can occur if the qualification of a new supplier is required. If delivery of material from the Company’s suppliers were interrupted for any reason, the Company may be unable to supply any of its product candidates for clinical trials.
Fair Value Measurements	Fair Value Measurements The carrying amounts for financial instruments consisting of cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their short maturities. Marketable securities are stated at their estimated fair values. The free share asset/liability is measured using a binomial-lattice pricing model and is reviewed each reporting period and adjusted, as needed and is expected to approximate fair value.
Leases	Leases The Company determines if an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether it has the right to control the identified asset. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and also include any lease payments made prior to or on lease commencement and exclude lease incentives and initial direct costs incurred, as applicable. As the implicit rate in the Company’s leases is generally unknown, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of remaining lease payments. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease in a similar economic environment. The Company gives consideration to its credit risk, term of the lease, total lease payments and adjusts for the impacts of collateral, as necessary, when calculating its incremental borrowing rates. The lease terms may include options to extend or terminate the lease when it is reasonably certain the Company will exercise any such options. Rent expense for the Company’s operating leases is recognized on a straight-line basis over the lease term. The Company has elected to not separate lease and non-lease components for its real estate and copier leases and, as a result, accounts for any lease and non-lease components as a single lease component. The Company has also elected to not apply the recognition requirement to any leases with a term of 12 months or less and does not include an option to purchase the underlying asset that the Company is reasonably certain to exercise.
Revenue Recognition	Revenue Recognition Effective January 1, 2018, the Company adopted the provisions of Accounting Standards Codification (“ASC”) Topic 606 - Revenue from Contracts with Customers (“ASC Topic 606”) using the modified retrospective method, resulting in a change to its accounting policy for revenue recognition. ASC Topic 606 establishes a unified model to determine how revenue is recognized. The Company’s contract revenues consist of strategic partnering collaboration agreements and research activity grants and licensing. Research and licensing agreements typically include upfront signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments and royalties on future licensee’s product sales. The Company has both fixed and variable consideration. Non-refundable upfront fees and funding of research and development activities are considered fixed, while milestone payments are identified as variable consideration. Sangamo’s research grants are typically multi-year agreements and provide for the reimbursement of qualified expenses for research and development as defined under the terms of the grant agreement. Revenues under research grant agreements are recognized when the related qualified research expenses are incurred. Deferred revenue represents the portion of research or license payments received and incurred but not earned. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account in ASC Topic 606. The Company’s performance obligations include license rights, development services and services associated with regulatory submission and approval processes. Revenues from research services are made under strategic partnering agreements and collaborations are generally recognized as the services are provided while revenues from non-refundable upfront fees are recognized over time either by measuring progress towards satisfaction of the relevant performance obligation, using input method or on a straight-line basis when a performance obligation is assumed to be satisfied evenly over a period of time (or when the entity has a stand-ready obligation). Significant management judgment is required to determine the level of effort required under an arrangement and the period over which the Company expects to complete its performance obligations under the arrangement which may include reimbursement rates for personnel costs, external reimbursable costs, estimated period of performance and estimating the progress towards the satisfaction of performance obligation. If the Company cannot reasonably estimate when its performance obligations either are completed or become inconsequential, then revenue recognition is deferred until the Company can reasonably make such estimates. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. The estimated period of performance and project costs, such as personnel and manufacturing cost, are reviewed quarterly and adjusted, as needed, to reflect the Company’s current assumptions regarding the timing of its deliverables. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the stand-alone selling price of each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. Related costs and expenses under these arrangements have historically approximated the revenues recognized. For the nine months ended September 30, 2019, revenues related to Kite Pharma, Inc. (“Kite”), a wholly-owned subsidiary of Gilead Sciences, Inc., Bioverativ Inc., (now Sanofi Genzyme, a global business unit of Sanofi S.A. (“Sanofi”)), and the Company's hemophilia A collaboration agreement with Pfizer represented 55%, 29% and 11%, respectively, of the Company’s total revenue. For the three months ended September 30, 2019, revenues related to Kite, Sanofi and the Company's hemophilia A collaboration agreement with Pfizer represented 40%, 40% and 16%, respectively, of the Company’s total revenue. During the nine months ended September 30, 2018, revenues related to the Company's hemophilia A collaboration agreement with Pfizer, Kite and Sanofi represented 46%, 29% and 19% respectively, of the Company’s total revenue. For the three months ended September 30, 2018, revenues related to the Company's hemophilia A collaboration agreement with Pfizer, Kite and Sanofi represented 44%, 38% and 10%, respectively, of the Company’s total revenue. Receivables from collaborations are typically unsecured and are concentrated in the biopharmaceutical industry. Accordingly, the Company may be exposed to credit risk generally associated with biopharmaceutical companies or specific to its collaboration agreements. To date, the Company has not experienced any losses related to these receivables. Funds received from third parties under contract or grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the arrangements because the activities under the contracts or grants are part of the Company’s development programs. Contract funds received are not refundable and are recognized when the related qualified research and development costs are incurred and there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue.
Recent Accounting Pronouncements	Not yet adopted Collaborative Arrangements In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (ASC Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASC Topic 808”), which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC Topic 606 when the counterparty is a customer. In addition, ASC Topic 808 precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance will be effective for the Company beginning January 1, 2020. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. Goodwill Impairment Testing In January 2017, the FASB issued ASU No. 2017-4, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test of Goodwill Impairment (“ASU 2017-4”). The new guidance simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. ASU 2017-4 requires goodwill impairment to be measured as the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of its goodwill. ASU 2017-4 requires prospective application and is effective for annual periods beginning after December 15, 2019. ASU 2017-4 will require the Company to amend its methodology for determining any goodwill impairment beginning in 2020. Recent Accounting Pronouncements Recently Adopted Simplified Disclosure In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification, as updated. These amendments eliminate, modify, or integrate into other SEC requirements certain disclosure rules. Among the amendments is the requirement to present an analysis of changes in stockholders’ equity in the interim financial statements included in quarterly reports on Form 10-Q. The analysis, which can be presented as a footnote or separate statement, is required for the current and comparative quarter and year-to-date interim periods. The amendments are effective for all filings made on or after November 5, 2018. As such, the Company adopted these SEC amendments on November 5, 2018 and has presented the analysis of changes in stockholders’ equity in these interim financial statements for September 30, 2019 and 2018 presented in this Quarterly Report on Form 10-Q. The Company’s adoption of these SEC amendments had no material effect on the Company’s reporting of financial position, results of operations, cash flows or stockholders’ equity. Accounting for Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-2, Leases (“ASC Topic 842”). ASC Topic 842 amends a number of aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a ROU asset and corresponding liability, measured at the present value of the lease payments. On January 1, 2019, the Company adopted ASC Topic 842 using the modified retrospective approach with a cumulative-effect adjustment of $0.9 million reflected as a decrease to the opening balance of accumulated deficit as of the adoption date. Results for the three and nine months ended September 30, 2019 are presented under ASC Topic 842. No prior period amounts were adjusted and continue to be reported in accordance with previous lease guidance, ASC Topic 840 — Leases (“ASC Topic 840”). ASC Topic 842 provides a number of optional practical expedients in transition. The Company elected the practical expedients to not reassess its prior conclusions about lease identification under the new standard, to not reassess lease classification, and to not reassess initial direct costs. The Company did not elect the practical expedient allowing the use-of-hindsight which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date and did not elect the practical expedient pertaining to land easements as this is not applicable to the current contract portfolio.

Organization, Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2019

The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019. The Condensed Consolidated Balance Sheet data at December 31, 2018 was derived from the audited consolidated financial statements included in Sangamo’s Annual Report on Form 10-K for the year ended December 31, 2018 (the “2018 Annual Report”) as filed with the SEC on March 1, 2019. The accompanying Condensed Consolidated Financial Statements and related financial information should be read in conjunction with the audited financial statements and footnotes thereto for the year ended December 31, 2018, included in the 2018 Annual Report.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates including critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities, including from acquisitions, and stock-based compensation. Estimates are based on historical experience and on various other market specific and other relevant assumptions that the Company believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates. In March 2019, the Company recorded an adjustment to revenue related to a change in estimate in connection with the hemophilia A collaboration agreement with Pfizer Inc. (“Pfizer”). This adjustment was a direct result of the increase in project scope during the first quarter of 2019 and the corresponding costs which resulted in a decrease in the measure of proportional performance. This adjustment decreased revenue by $3.0 million, increased net loss by $3.0 million and increased the Company’s basic net loss per share by $0.03 for the nine months ended September 30, 2019.

Foreign Currency Translation

The functional currency of the Company’s foreign subsidiaries is primarily the Euro. Assets and liabilities denominated in foreign currencies are translated to U.S. dollars using the exchange rates at the balance sheet date. Foreign currency translation adjustments are recorded as a component of Accumulated Other Comprehensive Income (Loss) (“AOCI”) within stockholders’ equity. Revenues and expenses from the Company’s foreign subsidiaries are translated using the monthly average exchange rates in effect during the period in which the transactions occur. Foreign currency transaction gains and losses are recorded in interest and other income, net, on the Company’s Condensed Consolidated Statements of Operations.

Reclassifications

Certain prior period amounts in the accompanying Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation. These reclassifications had no effect on the reported results of operations. The Company reclassified $0.6 million from Intangible assets to Other non-current assets on the Condensed Consolidated Balance Sheet as of December 31, 2018.

Cash and Cash Equivalents

Sangamo considers all highly-liquid investments purchased with original maturities of three months or less at the purchase date to be cash equivalents. Cash and cash equivalents consist of cash, deposits in demand money market accounts and commercial paper.

Marketable Securities

Sangamo classifies its marketable securities as available-for-sale and records its investments at estimated fair value based on quoted market prices or observable market inputs of almost identical assets, with the unrealized holding gains and losses included in AOCI.

The Company’s investments are subject to a periodic impairment review. The Company recognizes an impairment charge, if material; when a decline in the fair value of its investments below the cost basis is judged to be other-than-temporary. The Company considers various factors in determining whether to recognize an impairment charge, including the length of time and extent to which the fair value has been less than the Company’s cost basis, the financial condition and near-term prospects of the investee and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in the market value. Realized gains and losses on available-for-sale securities are included in other income, net, which are determined using the specific identification method.

Concentrations of Risk

Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to a concentration of credit risk to the extent of the fair value recorded in the Condensed Consolidated Balance Sheets. The Company invests cash that is not required for immediate operating needs primarily in highly liquid instruments that bear minimal risk. The Company has established guidelines relating to the quality, diversification, and maturities of securities to enable the Company to manage its credit risk. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents and investments and issuers of investments to the extent recorded on the Condensed Consolidated Balance Sheets.

Certain materials and key components that the Company utilizes in its operations are obtained through single suppliers. Since the suppliers of key components and materials must be named in an investigational new drug application filed with the U.S. Food and Drug Administration for a product, significant delays can occur if the qualification of a new supplier is required. If delivery of material from the Company’s suppliers were interrupted for any reason, the Company may be unable to supply any of its product candidates for clinical trials.

Fair Value Measurements

The carrying amounts for financial instruments consisting of cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their short maturities. Marketable securities are stated at their estimated fair values. The free share asset/liability is measured using a binomial-lattice pricing model and is reviewed each reporting period and adjusted, as needed and is expected to approximate fair value.

Leases

The Company determines if an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether it has the right to control the identified asset. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and also include any

lease payments made prior to or on lease commencement and exclude lease incentives and initial direct costs incurred, as applicable.

As the implicit rate in the Company’s leases is generally unknown, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of remaining lease payments. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease in a similar economic environment. The Company gives consideration to its credit risk, term of the lease, total lease payments and adjusts for the impacts of collateral, as necessary, when calculating its incremental borrowing rates. The lease terms may include options to extend or terminate the lease when it is reasonably certain the Company will exercise any such options. Rent expense for the Company’s operating leases is recognized on a straight-line basis over the lease term.

The Company has elected to not separate lease and non-lease components for its real estate and copier leases and, as a result, accounts for any lease and non-lease components as a single lease component. The Company has also elected to not apply the recognition requirement to any leases with a term of 12 months or less and does not include an option to purchase the underlying asset that the Company is reasonably certain to exercise.

Revenue Recognition

Effective January 1, 2018, the Company adopted the provisions of Accounting Standards Codification (“ASC”) Topic 606 - Revenue from Contracts with Customers (“ASC Topic 606”) using the modified retrospective method, resulting in a change to its accounting policy for revenue recognition. ASC Topic 606 establishes a unified model to determine how revenue is recognized.

The Company’s contract revenues consist of strategic partnering collaboration agreements and research activity grants and licensing. Research and licensing agreements typically include upfront signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments and royalties on future licensee’s product sales. The Company has both fixed and variable consideration. Non-refundable upfront fees and funding of research and development activities are considered fixed, while milestone payments are identified as variable consideration. Sangamo’s research grants are typically multi-year agreements and provide for the reimbursement of qualified expenses for research and development as defined under the terms of the grant agreement. Revenues under research grant agreements are recognized when the related qualified research expenses are incurred. Deferred revenue represents the portion of research or license payments received and incurred but not earned.

In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation.

A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account in ASC Topic 606. The Company’s performance obligations include license rights, development services and services associated with regulatory submission and approval processes. Revenues from research services are made under strategic partnering agreements and collaborations are generally recognized as the services are provided while revenues from non-refundable upfront fees are recognized over time either by measuring progress towards satisfaction of the relevant performance obligation, using input method or on a straight-line basis when a performance obligation is assumed to be satisfied evenly over a period of time (or when the entity has a stand-ready obligation). Significant management judgment is required to determine the level of effort required under an arrangement and the period over which the Company expects to complete its performance obligations under the arrangement which may include reimbursement rates for personnel costs, external reimbursable costs, estimated period of performance and estimating the progress towards the satisfaction of performance obligation. If the Company cannot reasonably estimate when its performance obligations either are completed or become inconsequential, then revenue recognition is deferred until the Company can reasonably make such estimates. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. The estimated period of performance and project costs, such as personnel and manufacturing cost, are reviewed quarterly and adjusted, as needed, to reflect the Company’s current assumptions regarding the timing of its deliverables.

As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the stand-alone selling price of each performance obligation identified in the contract. The Company uses key

assumptions to determine the stand-alone selling price which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. Related costs and expenses under these arrangements have historically approximated the revenues recognized.

For the nine months ended September 30, 2019, revenues related to Kite Pharma, Inc. (“Kite”), a wholly-owned subsidiary of Gilead Sciences, Inc., Bioverativ Inc., (now Sanofi Genzyme, a global business unit of Sanofi S.A. (“Sanofi”)), and the Company's hemophilia A collaboration agreement with Pfizer represented 55%, 29% and 11%, respectively, of the Company’s total revenue. For the three months ended September 30, 2019, revenues related to Kite, Sanofi and the Company's hemophilia A collaboration agreement with Pfizer represented 40%, 40% and 16%, respectively, of the Company’s total revenue. During the nine months ended September 30, 2018, revenues related to the Company's hemophilia A collaboration agreement with Pfizer, Kite and Sanofi represented 46%, 29% and 19% respectively, of the Company’s total revenue. For the three months ended September 30, 2018, revenues related to the Company's hemophilia A collaboration agreement with Pfizer, Kite and Sanofi represented 44%, 38% and 10%, respectively, of the Company’s total revenue. Receivables from collaborations are typically unsecured and are concentrated in the biopharmaceutical industry. Accordingly, the Company may be exposed to credit risk generally associated with biopharmaceutical companies or specific to its collaboration agreements. To date, the Company has not experienced any losses related to these receivables.

Funds received from third parties under contract or grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the arrangements because the activities under the contracts or grants are part of the Company’s development programs. Contract funds received are not refundable and are recognized when the related qualified research and development costs are incurred and there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue.

Recent Accounting Pronouncements

Not yet adopted

Collaborative Arrangements

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (ASC Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASC Topic 808”), which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC Topic 606 when the counterparty is a customer. In addition, ASC Topic 808 precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance will be effective for the Company beginning January 1, 2020. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Goodwill Impairment Testing

In January 2017, the FASB issued ASU No. 2017-4, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test of Goodwill Impairment (“ASU 2017-4”). The new guidance simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. ASU 2017-4 requires goodwill impairment to be measured as the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of its goodwill. ASU 2017-4 requires prospective application and is effective for annual periods beginning after December 15, 2019. ASU 2017-4 will require the Company to amend its methodology for determining any goodwill impairment beginning in 2020.

Recent Accounting Pronouncements

Recently Adopted

Simplified Disclosure

In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification, as updated. These amendments eliminate, modify, or integrate into other SEC requirements certain disclosure rules. Among the amendments is the requirement to present an analysis of changes in stockholders’ equity in the interim financial statements included in quarterly reports on Form 10-Q. The analysis, which can be presented as a footnote or separate statement, is required for the current and comparative quarter and year-to-date interim periods. The amendments are effective for all filings made on or after November 5, 2018. As such, the Company adopted these SEC amendments on November 5, 2018 and has presented the analysis of changes in stockholders’ equity in these interim financial statements for September 30, 2019 and 2018 presented in this Quarterly Report on Form 10-Q. The Company’s adoption of these SEC amendments had no material effect on the Company’s reporting of financial position, results of operations, cash flows or stockholders’ equity.

Accounting for Leases

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-2, Leases (“ASC Topic 842”). ASC Topic 842 amends a number of aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a ROU asset and corresponding liability, measured at the present value of the lease payments. On January 1, 2019, the Company adopted ASC Topic 842 using the modified retrospective approach with a cumulative-effect adjustment of $0.9 million reflected as a decrease to the opening balance of accumulated deficit as of the adoption date. Results for the three and nine months ended September 30, 2019 are presented under ASC Topic 842. No prior period amounts were adjusted and continue to be reported in accordance with previous lease guidance, ASC Topic 840 — Leases (“ASC Topic 840”).

ASC Topic 842 provides a number of optional practical expedients in transition. The Company elected the practical expedients to not reassess its prior conclusions about lease identification under the new standard, to not reassess lease classification, and to not reassess initial direct costs. The Company did not elect the practical expedient allowing the use-of-hindsight which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date and did not elect the practical expedient pertaining to land easements as this is not applicable to the current contract portfolio.