Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Sangamo Therapeutics, Inc. (“Sangamo” or the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles 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 generally accepted accounting principles 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, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017. The condensed consolidated balance sheet data at December 31, 2016 were derived from the audited consolidated financial statements included in Sangamo’s Annual Report on Form 10-K for the year ended December 31, 2016, (the “2016 Annual Report”), as filed with the SEC. 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, 2016, included in the 2016 Annual Report.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles 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, 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.
Revenue Recognition	Revenue Recognition Revenues from research activities made under strategic partnering agreements and collaborations are recognized as the services are provided when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes upfront signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments and royalties on future licensee’s product sales. For revenue agreements with multiple element arrangements, such as license and development agreements, entered into on or after January 1, 2011, the Company allocates revenue to each non-contingent element based on the relative selling price of each element. When applying the relative selling price method, the Company determines the selling price for each deliverable using Vendor Specific Objective Evidence (“VSOE”) of selling price or Third Party Evidence (“TPE”) of selling price. If neither exists, the Company uses Estimated Selling Price (“ESP”) for that deliverable. Revenue allocated is then recognized when the basic four revenue recognition criteria are met for each element. The collaboration and license agreements, as amended, if applicable, entered into with (i) Shire International GmbH, formerly Shire AG (“Shire”), in January 2012, and (ii) Bioverativ Inc. (“Bioverativ”), the blood disorder spin-off of Biogen Inc., formerly Biogen Idec MA Inc. (“Biogen”) in January 2014 were evaluated under these amended accounting standards. For the Company’s arrangement entered into May 2017 with Pfizer, Inc. (“Pfizer”), the Company recognizes revenue as a single unit of account as the license, research and development activities cannot be separated and therefore do not have standalone value. Additionally, the Company may be entitled to receive certain milestone payments which are contingent upon reaching specified objectives. These milestone payments are recognized as revenue in full upon achievement of the milestone if there is substantive uncertainty at the date the arrangement is entered into that the objectives will be achieved and if the achievement is based on the Company’s performance. Minimum annual sublicense fees are also recognized as revenue in the period in which such fees are due. Royalty revenues are generally recognized when earned and collectability of the related royalty payment is reasonably assured. The Company recognizes cost reimbursement revenue under collaborative agreements as the related research and development costs for services are rendered assuming all other applicable revenue recognition criteria have been met. Deferred revenue represents the portion of research or license payments received which have not been earned. 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. Revenue under grant agreements is recognized when the related qualified research expenses are incurred.
Recent Accounting Standards	Recent Accounting Standards In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-09, Compensation – Stock Compensation (Topic 718) (“ASU 2016-09”). ASU 2016-09 involves several aspects of the accounting for share-based transactions, including the income tax consequences, classification of awards as either equity or liabilities, how to account for forfeitures, and classification on the statement of cash flows. The amendments in this update are effective for the Company for its fiscal year 2017. As a result of the adoption of ASU 2016-09, the Company recognized current and prior excess tax benefits related to the exercise of options in its income tax provision. As a result of the Company’s historic and current losses and valuation allowance applied to its deferred tax assets, the gross cumulative effect when considering the federal and state tax impact is $7.5 million. The Company has elected to prospectively apply the amendments related to classifying cash flows related to excess tax benefits as an operating activity. For the quarter ended September 30, 2017 excess tax benefits were classified as an operating activity on the consolidated statement of cash flows, along with other income tax cash flows. The Company has made a policy election to account for forfeitures as they occur. This election was adopted using the prospective approach resulting in an immaterial cumulative effect on retained earnings at the beginning of the period. Prior to the adoption, forfeitures were accounted for using an estimated forfeiture rate. In February 2016, the FASB issued ASU No. 2016-02 Leases (“ASU 2016-02”). ASU 2016-02 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 right-of-use asset and corresponding liability, measured at the present value of the lease payments. The guidance will become effective for the Company beginning in the first quarter of 2019 with early adoption permitted and will be adopted using a modified retrospective approach. The Company is evaluating the impact of the adoption of this standard on its consolidated financial statements, and expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon adoption, which will increase the Company’s total assets and total liabilities as compared to amounts prior to adoption. In May 2014, the FASB issued ASU 2014-09 Revenue from Contracts with Customers (“ASU 2014-09”). This standard outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The main principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. ASU 2014-09 provides companies with two implementation methods: (i) apply the standard retrospectively to each prior reporting period presented (full retrospective application); or (ii) apply the standard retrospectively with the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings of the annual reporting period that includes the date of initial application (modified retrospective application). The Company elected to apply the modified retrospective application. This guidance is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. The Company has performed a preliminary assessment and continues to evaluate the impact of the pending adoption of ASU 2014-09 on its consolidated financial statements and has determined that the collaborations with Pfizer, Bioverativ, Shire, Dow AgroSciences LLC (“DAS”) and Sigma-Aldrich Corporation, which was acquired by Merck KGaA and renamed MilliporeSigma (“Sigma”) are within its scope. The Company is assessing the various components of these collaborations under ASC 2014-09 including the upfront license payment, milestones, and research and development services. At this time the Company is evaluating the impact to its financial position and results of operations upon adoption of ASU 2014-09.