Common stock exchange ratio.

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Net proceeds from issuance public offering.

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Purchase plan offering period.

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Purchase plan purchase period.

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- Definition

Share based compensation arrangement by share based payment award number of vesting installment.

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Share based compensation arrangement by share based payment award options expiration term.

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Share based compensation arrangement by share based payment award options maximum term for specified stock holder.

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Share based compensation arrangement by share based payment award purchase price of common stock percent for specified stockholder.

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No definition available.

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Share based compensation arrangement by share based payment award vesting percentage.

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Share based compensation arrangement by share based payment award vesting portion.

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Specified stockholder ownership percentage.

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Aggregate number of common shares reserved for future issuance.

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Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

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-Subparagraph (a)

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

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No definition available.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

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- Definition

Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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- Definition

Intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

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No definition available.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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No definition available.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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-SubTopic 10

-Section 50

-Paragraph 2

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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-SubTopic 10

-Section 50

-Paragraph 2

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of fully vested and expected to vest options that are exercisable.

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-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(2)

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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No definition available.

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- Definition

Amount per share or per unit of equity securities issued by non-development stage entity.

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No definition available.

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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No definition available.

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- Definition

Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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-Name Accounting Standards Codification

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Number of new stock issued during the period.

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Number of shares of common stock subject to repurchase or cancellation determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period. Common stock subject to repurchase are outstanding common shares that are contingently returnable (that is, subject to recall).

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Stockholders' Equity - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 25, 2014	Sep. 23, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred shares authorized	5,000,000us-gaap_PreferredStockSharesAuthorized
Proceeds from public offering of common stock, net of issuance costs	$ 93,796,000	$ 69,492,000
Stock option maximum term	5 years 26 days
Specified stockholder ownership percentage	10.00%
Purchase price of common stock percent under stock incentive plans for specified stockholder	110.00%
Stock option maximum term for specified stockholder	5 years
Share of common stock subject to a stock option or stock appreciation right	1sgmo_CommonStockExchangeRatio
Fixed ratio shares of common stock	1.33
Intrinsic value of options exercised	20,400,000	8,900,000	600,000
Options outstanding, Aggregate Intrinsic Value	50,766,000
Options exercisable, Aggregate Intrinsic Value	39,475,000
Options vested and expected to vest, aggregate intrinsic value	49,400,000	54,900,000	8,500,000
Restricted stock units awarded	488,000
Aggregate value of shares vested in period	9,100,000	4,100,000	100,000
Total payments for the employees' tax obligations to taxing authorities	4,556,000	2,015,000
2013 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of fair value per share of common stock on option grant date	100.00%
Stock options vesting period	4 years
Stock options expiration term	10 years
Stock reserved for issuance under plan	14,100,000
Additional shares authorized under 2013 stock incentive plan	4,400,000
Shares reserved for issuance of future awards	768,044
2004 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for issuance under plan	9,700,000
2010 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of fair value per share of common stock on option grant date	85.00%
Stock reserved for issuance under plan	2,100,000
Purchase plan offering period	2 years
Purchase plan purchase period	6 months
Shares reserved for issuance of future awards	1,420,560
Maximum [Member] \| 2013 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option maximum term	10 years
Stock Option Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares subject to repurchase rights	0
Stock Option Activity [Member] \| 2013 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based vesting rights	Options granted under the 2013 Plan generally vest over four years at a rate of 25 percent one year from the grant date and one thirty-sixth per month thereafter and expire ten years after the grant, or earlier upon employment termination.
Stock options granted vesting percentage	25.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based vesting rights	These awards will vest as follows: one-third of the award will vest in a series of three successive equal annual installments.
Restricted stock units awarded	488,000	392,500
Grant date fair value of restricted stock units awarded	$ 14.05	$ 12.12
Share-based compensation arrangement by share-based payment award, number of vesting installment	3
Share-based compensation arrangement by share-based payment award, vesting portion	0.33%
Shares withheld from issuance in order to pay employee taxes	309,102	167,138	0
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offering, common stock shares issued	4,444,444	7,015,000		4,444,444	7,015,000
Public offering price of common stock issued				$ 22.50	$ 10.58
Proceeds from public offering of common stock, net of issuance costs				$ 93,800,000	$ 69,500,000
Underwriters \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock, number of shares issued in transaction					915,000