Quarterly report pursuant to Section 13 or 15(d)

Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail)

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Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Revenue Recognition [Line Items]        
Total Research and Development Revenue $ 2,031 $ 648 $ 3,206 $ 2,408
JAPAN        
Revenue Recognition [Line Items]        
Total Research and Development Revenue 1,914 648 3,009 1,908
UNITED STATES        
Revenue Recognition [Line Items]        
Total Research and Development Revenue $ 117 $ 0 $ 197 $ 500