Australia Research and Development Tax Incentive	3 Months Ended
Australia Research and Development Tax Incentive	Mar. 31, 2015
Research and Development [Abstract]
Australia Research and Development Tax Incentive	9. Australia Research and Development Tax Incentive The Company’s wholly owned subsidiary, Zafgen Australia Pty Limited, which conducts core research and development activities on behalf of the Company is eligible to receive a 45% refundable tax incentive for qualified research and development activities. For the three months ended March 31, 2015 and 2014, $229 and $26, respectively, was recorded as a reduction to research and development expenses in the condensed consolidated statements of operations. These amounts represented 45% of the Company’s qualified research and development spending in Australia. The refund is denominated in Australian dollars and, therefore, the receivable is re-measured into U.S. dollars as of each reporting date. For the three months ended March 31, 2015 and 2014, the Company recorded in its condensed consolidated statements of operations unrealized foreign currency exchange gains (losses) of $(24) and $42, respectively, related to this tax incentive receivable. As of March 31, 2015 and December 31, 2014, the Company’s tax incentive receivable from the Australian government was $596 and $391, respectively.

The entire disclosure for research, development, and computer software activities, including contracts and arrangements to be performed for others and with federal government. Includes 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 in-process research and development acquired in a business combination consummated during the period.

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