XML 44 R34.htm IDEA: XBRL DOCUMENT v3.8.0.1
Australia Research and Development Tax Incentive - Additional Information (Detail) - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Research and Development Tax Incentive [Line Items]      
Unrealized foreign currency transaction gains (losses) $ (14,000) $ 21,000  
Research and Development [Member]      
Research and Development Tax Incentive [Line Items]      
Percentage of reduction in research and development costs 43.50%    
Zafgen Australia Pty Limited [Member] | Australia [Member]      
Research and Development Tax Incentive [Line Items]      
Tax incentive receivable $ 1,500,000   $ 900,000
Zafgen Australia Pty Limited [Member] | Research and Development [Member]      
Research and Development Tax Incentive [Line Items]      
Percentage of refundable tax incentive 43.50%    
Reduction to research and development expenses $ 600,000 0  
Zafgen Australia Pty Limited [Member] | Maximum [Member]      
Research and Development Tax Incentive [Line Items]      
Unrealized foreign currency transaction gains (losses) $ 100,000 $ 100,000