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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2018
Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]      
Award amount $ 18,700,000    
Award termination date May 31, 2019    
Matching funds requirement   50.00%  
Increase in research fund   $ 9,300,000  
Award term   3 years  
Total matching funding available   $ 4,200,000 $ 1,600,000
Current funding available   5,100,000 7,700,000
Current funding received   9,600,000 2,600,000
Litigation reserves   $ 0 $ 0