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
Mar. 31, 2019
Mar. 31, 2018
Revenue Recognition [Line Items]    
Total Research and Development Revenue $ 6,413 $ 231
JAPAN    
Revenue Recognition [Line Items]    
Total Research and Development Revenue 6,413 163
UNITED STATES    
Revenue Recognition [Line Items]    
Total Research and Development Revenue $ 0 $ 68