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Australia Research and Development Tax Incentive - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Research and Development Tax Incentive [Line Items]
Unrealized foreign currency exchange gains (losses)	$ (29,000)	$ 14,000
Zafgen Australia Pty Limited [Member]
Research and Development Tax Incentive [Line Items]
Research and development expense	0
Unrealized foreign currency exchange gains (losses)	(200,000)
Zafgen Australia Pty Limited [Member] | Australia [Member]
Research and Development Tax Incentive [Line Items]
Tax incentive receivable	$ 200,000		$ 200,000
Zafgen Australia Pty Limited [Member] | Maximum [Member]
Research and Development Tax Incentive [Line Items]
Unrealized foreign currency exchange gains (losses)		$ 100,000
Research and Development [Member] | Zafgen Australia Pty Limited [Member]
Research and Development Tax Incentive [Line Items]
Percentage of refundable tax incentive	43.50%	43.50%
Reduction to research and development expenses		$ 100,000
Percentage of reduction in research and development costs		43.50%

X

- Definition

Amount before tax of foreign currency transaction unrealized gain (loss) recognized in the income statement.

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-Publisher FASB
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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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- Definition

The percentage to be refunded pertaining to the tax incentive for qualified research and development activities.

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The percentage of research and development costs to be reduced.

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Research and Development Tax Incentive [Line Items]

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Tax incentive receivable.

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