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Australia Research and Development Tax Incentive - Additional Information (Detail) - Spero Potentiator Australia Pty Limited [Member] - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Australia [Member]      
Schedule Of Income Tax [Line Items]      
Tax incentive receivable $ 1,900,000   $ 1,900,000
Research and Development Expenses [Member]      
Schedule Of Income Tax [Line Items]      
Percentage of refundable tax incentive 43.50%    
Reduction to research and development expenses $ 100,000 $ 0