Australia Research and Development Tax Incentive - Additional Information (Detail) - Spero Potentiator Australia Pty Limited [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Australia [Member]
Schedule Of Income Tax [Line Items]
Tax incentive receivable	$ 1.4		$ 1.4		$ 1.1
Research and Development Expenses [Member]
Schedule Of Income Tax [Line Items]
Percentage of refundable tax incentive			43.50%
Reduction to research and development expenses	$ 0.2	$ 0.4	$ 0.2	$ 0.4