Common Stock Exchange Ratio

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- Definition

Non employee service share based compensation non-vested awards compensation not yet recognized stock options.

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- Definition

Nonemployee service share-based compensation, non-vested awards, compensation cost not yet recognized, period for recognition.

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- Definition

Share based compensation arrangement by share based payment award percentage of shares outstanding.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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- Definition

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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- Definition

General descriptive information regarding an arrangement under which employees and directors receive: (a) awards of equity shares, equity share options, or other equity instruments; or (b) the entity incurs liabilities to them: (1) in amounts based, at least in part, on the price of the entity's shares or other equity instruments; or (2) that require or may require settlement by issuance of the entity's shares. Such an arrangement is usually provided to employees and directors to compensate them, provide performance incentives to them, and to attract or retain their services. May also include pertinent information particular to a plan that is not elsewhere specified in the taxonomy.

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- Definition

Discount rate from fair value on offering date that participants pay for shares.

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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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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

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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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

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- Definition

Percentage of vesting of share-based compensation awards.

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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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Equity-based Compensation and Equity Incentive Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Aug. 28, 2017 shares	Aug. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exchange ratio of common stock			0.5532
Equity-based compensation expense	$ 4,317,000	$ 2,652,000
Weighted average grant date fair value per share of options granted to employees \| $ / shares	$ 6.35
Total fair value of awards vested	$ 3,300,000
Employee unrecognized compensation expense	$ 8,400,000
Employee unrecognized compensation cost, period of recognition	2 years 7 months 6 days
Non-employee unrecognized compensation expense	$ 53,000,000
Non-employee unrecognized compensation cost, period of recognition	2 years 4 months 24 days
Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense	$ 956,000	$ 508,000
Employee unrecognized compensation expense	$ 200,000
Employee unrecognized compensation cost, period of recognition	1 year 7 months 6 days
Non-employee unrecognized compensation expense	$ 0
Granted \| shares	0	1,062,794
Vested \| shares	186,332	671,204
Restricted Common Stock \| 2017 Reorganization
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted \| shares		1,059,912
Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense		$ 132,000
Employee unrecognized compensation expense	$ 0
Units issued \| shares	0	0
Restricted Common Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense		$ 56,000
Vested \| shares		37,770
Unrecognized compensation expense	$ 0
Private Synlogic \| Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense	$ 26,000
Employees and Nonemployees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted \| shares	919,496	1,281,647
Equity-based compensation expense	$ 3,200,000	$ 2,000,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of discount for employees under ESPP	15.00%
Purchase price as a percentage of fair value under ESPP	85.00%
Plan 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock option and stock purchase rights available for grant (in shares) \| shares				647,893
Percentage of shares outstanding	5.00%
Award vesting description	Incentive units issued by Synlogic, LLC under the 2015 LLC Plan generally vested 25% after one year and ratably monthly thereafter over the next 36 months.
Options vested period	36 months
Plan 2015 \| After One Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awards, vesting percentage	25.00%
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock option and stock purchase rights available for grant (in shares) \| shares			1,753,061
2017 Plan \| Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted \| shares		2,884
2015 and 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants \| shares	477,414
Granted \| shares	919,496
Modifications in Equity Awards \| Separation of Former Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	$ 700,000